Hydrogen Fuel Systems

Increase the fuel economy of your engine.

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Hydrogen fuel systems used in combating and solving greenhouse  carbon dioxide generation from Coal Fired Power stations

Recently Hydrogen Fuel systems pty ltd  have expanded their horizon from  producing Hydrogen  for use in internal combustion engines , to use in developing a system to help eliminate  waste , greenhouse gas, carbon dioxide and generating organic fuels by hydrogenation which are recycled  , increasing the chemical thermodynamic  efficiency of the coal burning reaction.

Hydrogen fuel systems pty ltd systems have a The major advantage over other competitor systems in their extremely high efficiency, High output and minimal wasted thermal energy produced.  Basically , much/ much more input electrically  energy is converted into hydrogen gas which is  used in the all important Hydrogenation reactions of effluent gas  from burning coal to produce  and recycle  and reclaim waste  thermal energy.

Over the next 12 months , with federal and state funding, developments and results  will be published   on this site === aim to help prevent / stem/ reduce Greenhouse gas output and global  warming..   Bookmark this site / page for information on developments 

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Hydrogen-Enhanced Combustion Engine Could Improve Gasoline Fuel Economy by 20% to 30%

Hydrogen-Enhanced Combustion Engine Could Improve Gasoline Fuel Economy by 20% to 30%

5 November 2005

An HECE test engine

Work being done by ArvinMeritor, IAV (Ingenieursgesellshaft für Auto und Verkehr) and MIT on enhancing gasoline combustion with a small hydrogen gas stream is pointing toward a potential estimated improvement in gasoline fuel economy of 20% to 30%, depending upon the baseline engine.

Writing in the October issue of MTZ (Motortechnische Zeitschrift), Utz-Jens Beister from IAV and Rudy Smaling from ArvinMeritor describe their progress with the Hydrogen-Enhanced Combustion Engine (HECE) concept, as applied to an SUV-class 3.2-liter V6 test engine.

The premise of HECE, on which the research collaborative has been working for a number of years, is that the addition of a small amount of hydrogen to the cylinder charge can allow homogeneous charge ultra-lean-burn combustion engines to operate much leaner than otherwise possible.

That in itself is not a new discovery. What brings HECE closer to operational reality is the ArvinMeritor/MIT on-board, compact plasma reformer (earlier post) that can take a fraction of the conventional fuel, reform it in real-time and add the resulting hydrogen-rich gas to the remaining fuel-air mixture flowing into the engine.

In the plasma fuel reformer, air is metered into a plasma generator located upstream of a combustor. High voltage is applied to the air stream, forming high-temperature plasma. This high-temperature plasma torch flows into the combustor, initiating vigorous combustion of a rich fuel-air mixture. Within the plasma fuel reformer, partial oxidation reactions occur in the high-temperature gas phase created by the plasma, eliminating the need for a reforming catalyst.

The shift of combustion limits with hydrogen-enhanced combustion.

Adding hydrogen gas to the homogeneous fuel charge improves the ignitability of the mixture, and increases flame speed and combustion stability. In theory, the combination of a lean-burn engine with the plasma reformer could support an ultra-lean and turbocharged engine that would reduce NOx emissions to the point of not requiring aftertreatment in the exhaust stream.

Researchers at the Sloan Automotive Laboratory at MIT also discovered that both hydrogen and carbon monoxide (both products of the partial oxidation process of the reformer) act as octane enhancers. Adding the reformed fuel gas to the engine thus also supports a substantial increase in compression ratio.

Once an engine is developed that operates ultra-lean, is turbocharged—or super-charged—and is better able to withstand engine knock, engine downsizing while maintaining performance becomes a credible option that can lead to significant additional fuel economy and performance benefits.

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http://hydrogenfuelsystems.com.au/

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http://hydrogenfuelsystems.com.au/

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Murdoch University research report hydrogen use with diesel and petyrol fueled engines

http://researchrepository.murdoch.edu.au/2079/1/Young_2008.pdf

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Murdoch University research report hydrogen use with diesel and petyrol fueled engines

http://researchrepository.murdoch.edu.au/2079/1/Young_2008.pdf      

USES budget , cheap and ineffective US design that wastes much more energy than systems produced by hydrogenfuelsystems pty ltd    ,,,, yet still makes some significant savings.... but no where near the savings from HFS systems

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http://hydrogenfuelsystems.com.au/

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http://hydrogenfuelsystems.com.au/

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GUIDELINES FOR USE OF HYDROGEN FUEL IN COMMERCIAL VEHICLES

http://www.hho4free.com/documents/Guidelines-H2-Fuel-in-CMVs-Nov2007.pdf

GUIDELINES FOR USE OF HYDROGEN FUEL IN COMMERCIAL VEHICLES Final Report November 2007 FOREWORD This document is intended to be a safety reference for commercial vehicle fleet owners and operators that use vehicles or auxiliary power units powered by hydrogen. It was designed to provide commercial vehicle owners and operators with a basic understanding of the properties and characteristics of hydrogen, descriptions of the types of systems that might use hydrogen fuel on commercial vehicles, and practical guidelines for the safe use of hydrogen, both on vehicles and in vehicle maintenance and storage facilities. Hydrogen properties and characteristics are significantly different from those of other commercial motor fuels, such as gasoline and diesel fuel, and commercial vehicle systems that use hydrogen fuel can also be significantly different from typical gasoline or diesel engines. An understanding of these differences is important to understanding what the operator of a vehicle powered by hydrogen should and should not do in order to maintain safety during transportation. NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or the use thereof. The contents do not necessarily reflect the official policy of the Department of Transportation. This report does not constitute a standard, specification, or regulation. The United States Government does not endorse products or manufacturers. Trade or manufacturers’ names appear herein only because they are considered essential to the objective of this document. Technical Report Documentation Page (Form 1700.7) 1. Report No. FMCSA-RRT-07-020 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle: Guidelines for Use of Hydrogen Fuel in Commercial Vehicles 5. Report Date: November 2007 6. Performing Organization Code 7. Author(s): John M. Simon, CSP, Booz Allen Hamilton Inc. Stephen Brady, Booz Allen Hamilton Inc. Dana Lowell, M. J. Bradley & Associates Michael Quant, Booz Allen Hamilton Inc. 8. Performing Organization Report No. 9. Performing Organization Name and Address: 10. Work Unit No. (TRAIS) Booz Allen Hamilton Inc. 444 S. Flower Street, Suite 1850 Los Angeles, California 90071 11. Contract or Grant No. GS-23F-0025K 13. Type of Report and Period Covered Final Report 12. Sponsoring Agency Name and Address: U.S. Department of Transportation Federal Motor Carrier Safety Administration Technology Division (MC-RRT) 1200 New Jersey Ave. SE Washington, DC 20590 14. Sponsoring Agency Code FMCSA 15. Supplementary Notes: 16. Abstract: Over the next 50 years, hydrogen use is expected to grow dramatically as an automotive and electrical power source fuel. As hydrogen becomes commercially viable, the safety concerns associated with hydrogen systems, equipment, and operation are of concern to the commercial motor vehicle industry. This report is intended to provide guidelines for use of hydrogen fuel as an alternative fuel by a commercial vehicle fleet operator to ensure long-term safe operation. 17. Key Words: alternative fuel, APU, auxiliary power units, buses, commercial vehicles, compressed fuel cell, guidelines, hydrogen, hydrogen gas, hydrogen injection system, hydrogen internal combustion engine, hydrogen safety, liquefied hydrogen, motorcoaches, trucks 18. Distribution Statement No restrictions. 19. Security Classif. (of this report) Unclassified 20. Security Classif. (of this page) Unclassified 21. No. of Pages: 94 22. Price Form DOT F 1700.7 (8-72) Reproduction of completed page authorized. SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol LENGTH LENGTH in Inches 25.4 millimeters mm mm millimeters 0.039 inches in ft Feet 0.305 meters m m meters 3.28 feet ft yd Yards 0.914 meters m m meters 1.09 Yards yd mi Miles 1.61 kilometers km km kilometers 0.621 miles mi AREA AREA in2 square inches 645.2 square millimeters mm2 mm2 square millimeters 0.0016 square inches in2 ft2 square feet 0.093 square meters m2 m2 square meters 10.764 square feet ft2 yd2 square yards 0.836 square meters m2 m2 square meters 1.195 square yards yd2 ac Acres 0.405 hectares ha ha hectares 2.47 acres ac mi2 square miles 2.59 square kilometers km2 km2 square kilometers 0.386 square miles mi2 VOLUME VOLUME fl oz fluid ounces 29.57 milliliters ml ml milliliters 0.034 fluid ounces fl oz gal Gallons 3.785 liters l l liters 0.264 gallons gal ft3 cubic feet 0.028 cubic meters m3 m3 cubic meters 35.71 cubic feet ft3 yd3 cubic yards 0.765 cubic meters m3 m3 cubic meters 1.307 cubic yards yd3 MASS MASS oz Ounces 28.35 grams g g grams 0.035 ounces oz lb Pounds 0.454 kilograms kg kg kilograms 2.202 pounds lb T short tons (2000 lbs) 0.907 megagrams Mg Mg megagrams 1.103 short tons (2000 lbs) T TEMPERATURE (exact) TEMPERATURE (exact) °F Fahrenheit 5(F-32)/9 Celsius °C °C Celsius 1.8 C + 32 Fahrenheit °F Temperature or (F-32)/1.8 temperature temperature temperature ILLUMINATION ILLUMINATION fc foot-candles 10.76 lux lx lx Lux 0.0929 foot-candles fc fl foot-Lamberts 3.426 candela/m2 cd/m2 cd/m2 candela/m2 0.2919 foot-Lamberts fl FORCE and PRESSURE or STRESS FORCE and PRESSURE or STRESS lbf pound-force 4.45 newtons N N newtons 0.225 pound-force lbf psi pound-force per square inch 6.89 kilopascals kPa kPa kilopascals 0.145 pound-force per square inch psi * SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. ACKNOWLEDGEMENTS This document was prepared by Booz Allen Hamilton Inc. and M.J. Bradley & Associates, Inc., under contract GS-23F-0025K with the Federal Motor Carrier Safety Administration (FMCSA), a subdivision of the U.S. Department of Transportation (DOT). The FMCSA project manager for this project was Mr. Quon Kwan, the Booz Allen Hamilton project manager was Mr. John Simon, and the principal author of this document was Mr. Dana Lowell of M.J. Bradley & Associates. The authors are grateful to Mr. Paul Scott, ISE Corporation; Mr. Chris Morgan and Mr. Michael Chafee, California Highway Patrol; and Mr. Craig Michels, Alameda-Contra Costa Transit District for providing extensive peer review comments. The authors would like to thank Mr. William Chernicoff of the DOT Research and Innovative Technology Administration for lending his expertise to help guide the project, and Mr. Bill Parsley of Quest Consulting Group for his help with technical editing. The authors would also like to thank the following organizations and individuals for hosting project team members and providing background information and valuable insights: the U.S. Environmental Protection Agency, Mr. Dennis Johnson; The California Fuel Cell Partnership, Mr. Adam Gromis, Ms. Jennifer Hamilton, Mr. Matthew Forrest, and Ms. Andrea Labue; the California Highway Patrol, Mr. Chris Morgan and Mr. Mike Chafee; the Santa Clara Valley Transportation Authority, Mr. Arthur Douwes; the Alameda Contra-Costa Transit District, Mr. Jaime Levin, Mr. Bob Bithell, Ms. Mallory Nestor-Brush, and Mr. Doug Byrne; ISE Corporation, Dr. Paul Scott, Mr. Jayson Cannon; UTC Power, Mr. Matthew Riley; Sunline Transit Agency, Mr. Tommy Edwards, Mr. Frank Shardy and Mr. Polo Del Toro; Daimler Chrysler Research & Technology North America, Mr. Joe Impullitti; and United Parcel Service, Mr. Jim Breeher and Mr. Adam Spitz, and Delphi, Mr. Steve Shafer. TABLE OF CONTENTS acronyms...................................................................................................................................... IV executive summary...................................................................................................................... VI 1. INTRODUCTION.................................................................................................................1 1.1 BACKGROUND ...........................................................................................................1 1.2 HYDROGEN USE AS A MOTOR FUEL....................................................................2 1.3 HYDROGEN STORAGE ON VEHICLES.................................................................11 1.4 REFORMING OF LIQUID FUELS............................................................................17 1.5 ELECTROLYSIS OF WATER...................................................................................19 2. PROPERTIES OF HYDROGEN......................................................................................21 2.1 GASEOUS HYDROGEN............................................................................................21 2.2 LIQUID HYDROGEN ................................................................................................26 2.3 COMPARISON OF HYDROGEN TO OTHER MOTOR FUELS ............................28 2.4 HYDROGEN SAFETY PRINCIPLES........................................................................30 3. ..........................................................................................................................34 GUIDELINES FOR DESIGN AND OPERATION OF HYDROGEN SYSTEMS ON VEHICLES 3.1 GASEOUS HYDROGEN SYSTEMS.........................................................................34 3.2 LIQUID HYDROGEN SYSTEMS .............................................................................39 3.3 HIGH VOLTAGE SYSTEMS.....................................................................................43 3.4 LIQUID FUEL REFORMERS....................................................................................45 3.5 HYDROGEN INJECTION SYSTEMS.......................................................................46 4. .......................................................................................................................48 GUIDELINES FOR DESIGN AND OPERATION OF HYDROGEN FUELING FACILITIES 4.1 COMPRESSED HYDROGEN FUELING..................................................................48 4.2 LIQUID HYDROGEN FUELING ..............................................................................54 5. .......................................................................................................................59 GUIDELINES FOR DESIGN AND OPERATION OF VEHICLE MAINTENANCE FACILITIES 5.1 .......................................................................................................................60 DESIGN 5.2 OPERATION AND MAINTENANCE.......................................................................62 5.3 FACILITY SAFETY PLAN........................................................................................62 i 6. ................................................................................................64 EMERGENCY RESPONSE FOR PERSONNEL ASSIGNED TO VEHICLES CARRYING HYDROGEN 6.1 RESPONDING TO AN INCIDENT ...........................................................................64 6.2 DETECTING HYDROGEN LEAKS..........................................................................65 6.3 HYDROGEN FIRES ...................................................................................................66 6.4 LIQUID HYDROGEN ................................................................................................67 APPENDICES APPENDIX A: OPERATION OF A FUEL CELL ..................................................................69 PEM FUEL CELL ................................................................................................................69 SOFC FUEL CELL ..............................................................................................................70 APPENDIX B: CODES AND STANDARDS AND RECOMMENDED PRACTICES ........72 FEDERAL REGULATIONS ...............................................................................................72 NATIONAL FIRE PROTECTION ASSOCIATION STANDARDS..................................74 COMPRESSED GAS ASSOCIATION ...............................................................................74 SOCIETY OF MECHANICAL ENGINEERS (ASME) STANDARDS.............................75 SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) STANDARDS ................................75 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO).....................76 GLOSSARY..................................................................................................................................77 REFERENCES.............................................................................................................................79 LIST OF TABLES Table 1. Why Hydrogen?................................................................................................................ 1 Table 2. Challenges of Using Hydrogen......................................................................................... 3 Table 3. Comparison of Fuel Cells to ICEs and Batteries .............................................................. 4 Table 4. Hydrogen Flammability Range and Ignition Energy...................................................... 22 Table 5. Leak Profiles of Gaseous Hydrogen, Liquid Hydrogen, and Diesel Fuel ...................... 29 ii iii LIST OF FIGURES Figure 1. Operation of a Proton Exchange Membrane Fuel Cell ................................................... 5 Figure 2. PEM Fuel Cell Stack ....................................................................................................... 5 Figure 3. Generic PEM Fuel Cell Engine Schematic ..................................................................... 6 Figure 4. PEM Fuel Cell Engine and Electric Drive Motor for a Transit Bus ............................... 7 Figure 5. Wells-to-Wheels Fuel Use for Different Propulsion Systems......................................... 8 Figure 6. Operation of an SOFC Fuel Cell ..................................................................................... 9 Figure 7. Ford V10 Hydrogen Engine .......................................................................................... 10 Figure 8. Gaseous Hydrogen Storage System............................................................................... 13 Figure 9. Liquid Hydrogen Fuel System....................................................................................... 15 Figure 10. Liquid Hydrogen Fueling ............................................................................................ 16 Figure 11. Onboard Methanol Reformer for a Bus....................................................................... 19 Figure 12. Electrolysis of Water to Produce Hydrogen and Oxygen ........................................... 20 Figure 13. Hydrogen Flame .......................................................................................................... 23 Figure 14. High-Pressure Storage Vessel Qualification Tests...................................................... 25 Figure 15. Liquid Hydrogen Temperature.................................................................................... 26 Figure 16. Hydrogen Vehicle Label in Accordance with SAE J2578 .......................................... 31 Figure 17. Fire Triangle ................................................................................................................ 31 Figure 18. Hazardous Voltage Symbol......................................................................................... 43 Figure 19. Hydrogen Tube Trailer................................................................................................ 48 Figure 20. Liquid Hydrogen Storage Tank and Vaporizer ........................................................... 49 Figure 21. Natural Gas Reformer.................................................................................................. 50 Figure 22. Compressed Hydrogen Dispenser ............................................................................... 50 Figure 23. Compressed Hydrogen Fuel Nozzle............................................................................ 51 Figure 24. Hydrogen Fueling Station............................................................................................ 51 Figure 25. Liquid Hydrogen Storage Station................................................................................ 54 Figure 26. Liquid Hydrogen Fueling Nozzle and Vehicle Fuel Port............................................ 55 Figure 27. Hydrogen Detector Located at Ceiling Level.............................................................. 60 Figure 28. Explosion Proof Switches............................................................................................ 61 Figure 29. Hydrogen Leak Detector ............................................................................................. 66 Figure 30. Hydrogen Vehicle Fire Showing Ignited Hydrogen Released from PRD................... 67 Figure 31. PEM Fuel Cell Construction ....................................................................................... 69 Figure 32. SOFC Construction Tubular Design ........................................................................... 71 ACRONYMS APU Auxiliary power unit: For commercial trucks, APUs are small engines used to provide power for auxiliary loads, such as heating, air conditioning, and lighting in sleeper berths. In most trucks without an APU, this power for auxiliary loads is provided by the main engine. The use of an APU allows the operator to shut off the main engine while resting. CNG Compressed natural gas CO Chemical symbol for carbon monoxide CO2 Chemical symbol for carbon dioxide H2 Chemical symbol for molecular hydrogen ICE Internal combustion engine: A heat engine in which burning (combustion) of fuel takes place in a confined space called a combustion chamber. Diesel and gasoline engines are both internal combustion engines. IR Infrared: The part of the electromagnetic radiation spectrum in which the wavelength of the radiation is longer than that of visible light but shorter than that of radio waves. Infrared radiation has wavelengths between 750 nanometers and one millimeter. KW Kilowatt: A unit of measure for power, equal to 1,000 watts. One kilowatt is equal to 1.34 horsepower. PEM Proton Exchange Membrane: A semi-permeable membrane made of a plastic-like material, designed to allow hydrogen ions (protons) to pass through, but to be impermeable to gases like hydrogen and oxygen. In a proton exchange membrane fuel cell, the membrane acts as the electrolyte, separating the fuel and oxygen, but passing protons from the anode to the cathode. PRD/TRD Pressure relief device/thermal relief device: A device used to protect from overpressure inside a high-pressure storage tank. When the pressure inside the tank rises above a set threshold, a rupture disc inside the PRD breaks, allowing the tank to vent to reduce pressure inside. A TRD includes a material that melts at a set temperature. When the material melts, it opens the device, allowing the tank to vent. TRDs are used because exposure of a high-pressure tank to increased temperatures will increase pressure inside the vessel. psi Pounds per square inch: A unit of measure for pressure. psia Pounds per square inch absolute: Absolute pressure is measured relative to a perfect vacuum, so that the absolute measurement of atmospheric air pressure at sea level is 14.7 psia. psig Pounds per square inch gauge: Gauge pressure is measured relative to atmospheric air pressure at sea level, so that gauge measurements of atmospheric pressure at sea level are always 0 psig. iv v SOFC Solid Oxide Fuel Cell: A type of high-temperature hydrogen fuel cell that uses a solid metal oxide electrolyte, which passes oxygen ions from the cathode to the anode. Solid oxide fuel cells do not need to be fueled with pure hydrogen gas because they support automatic reforming of gaseous hydrocarbon fuels such as methane within the device. UV Ultraviolet: The part of the electromagnetic radiation spectrum in which the wavelength of the radiation is shorter than that of visible light but longer than that of x-rays. Ultraviolet radiation has wavelengths between 10 and 380 nanometers. VAC Volts, alternating current: A volt is a measure of electric potential or electromotive force. Electrical current is the flow of electrons in one direction. With alternating current, the magnitude and direction of the current varies cyclically, usually as a sine wave. Electric generators produce alternating current. VDC Volts, direct current: A volt is a measure of electric potential or electromotive force. Electrical current is the flow of electrons in one direction. With direct current, the magnitude of the current may vary, but the direction of the current is constant. Batteries and fuel cells produce direct current. EXECUTIVE SUMMARY Today, virtually all commercial trucks are powered by diesel fuel, while private cars are fueled by gasoline. Supported by our National Energy Policy, a new generation of technologies is currently being developed that allow the use of hydrogen as a fuel to power cars and trucks. In the future, hydrogen may be used in one of three ways to power vehicles: • To produce electricity in a fuel cell, • As a replacement for gasoline or diesel fuel in an internal combustion engine,1 or • As a supplement to gasoline or diesel fuel used in an internal combustion engine. This document is intended to be a safety reference for commercial vehicle fleet owners and operators that use vehicles or auxiliary power units powered by hydrogen fuel. It was designed to provide commercial vehicle owners and operators with a basic understanding of the properties and characteristics of hydrogen, descriptions of the types of systems that might use hydrogen fuel on commercial vehicles, and practical guidelines for the safe use of hydrogen, both on vehicles and in vehicle maintenance and storage facilities. Hydrogen is the most abundant element in our universe. In addition to being a component of all living things, hydrogen and oxygen together make up water, which covers 70 percent of the earth. In its pure form, hydrogen is a gas at normal temperatures and pressures; it is the lightest gas (even lighter than helium), with only 7 percent of the density of air. If you get it cold enough (-423°F), gaseous hydrogen will liquefy, and it can be transported and stored in this form. There is virtually no “free” hydrogen on earth—all of it is combined with other elements (mostly oxygen or carbon) in other substances. Every molecule of water contains two hydrogen atoms and one oxygen atom. Hydrocarbon fuels such as coal, gasoline, diesel, and natural gas also contain hydrogen. In the case of gasoline and diesel fuel, there are approximately two hydrogen atoms for every carbon atom, while natural gas contains four hydrogen atoms for every carbon atom. To be used as a fuel, hydrogen is typically separated from either water (via electrolysis) or from a hydrocarbon fuel (via reforming). Regardless of whether hydrogen fuel will be used in a fuel cell main engine, a fuel cell APU, or an internal combustion engine, there are different ways that it can be stored on the vehicle. Some fuel stations include liquid hydrogen storage, but on the vehicle, hydrogen is usually stored as a gas at high pressure. It is also possible to store a liquid fuel (gasoline, diesel, or methanol) onboard a vehicle and then use an onboard reformer to separate the hydrogen just before it is used in the fuel cell engine. While this requires additional equipment on the vehicle, it removes the need for high-pressure gas storage. These different storage technologies can introduce significantly different potential hazards, including very high pressure (gaseous hydrogen storage), very low temperature (liquid hydrogen storage), or high temperature (liquid fuel reforming). 1 Natural gas can also be used to power an internal combustion engine, and hydrogen can be used to supplement this fuel as well. This document does not address natural gas engines. vi All motor fuels, including diesel fuel, gasoline, and natural gas also pose risks of fire and explosion if handled improperly. Hydrogen is no different. While there are risks, hydrogen can be as safe, or safer, than diesel and other fuels when vehicles and fuel stations are designed and operated properly. All fuels require particular design and handling practices based on their properties, and all present certain hazards when mishandled. Understanding the properties of hydrogen is necessary to understanding what is required to use it safely. Hydrogen gas is colorless, odorless, tasteless, and noncorrosive—and it is nontoxic to humans. It has the second widest flammability range in air of any gas, but leaking hydrogen gas rises and diffuses to a nonflammable mixture quickly. Hydrogen ignites very easily and burns hot, but tends to burn out quickly. A hydrogen flame burns very cleanly, producing virtually no soot, which means that it is also virtually invisible. The extremely low temperature of liquid hydrogen poses a severe frostbite hazard to exposed skin. In some ways, a gaseous hydrogen fuel leak is less dangerous than a leak of diesel fuel or gasoline. Leaking diesel fuel and gasoline can puddle and spread over a large area, and the puddles will persist because they evaporate slowly. Gaseous hydrogen leaks tend to be vertical, with only a relatively narrow area/volume in which a flammable mixture exists—the hydrogen quickly rises and dissipates in open air to nonhazardous levels. If designed properly, the most likely location of a major hydrogen leak from a vehicle will be through the pressure relief device (PRD) on the hydrogen fuel storage cylinders, which should vent away from the occupied area of the vehicle. PRDs are designed to vent the entire contents of a hydrogen tank in only a few minutes—after which there is no lingering risk of hydrogen fire or explosion if the release was in the open air. Large hydrogen leaks inside buildings are more dangerous unless the facility has been designed to evacuate the leaked gas and to minimize ignition sources at ceiling level. Leaking liquid hydrogen can pool and spread, but will quickly evaporate as it is heated by the surrounding air. The distance it will spread and the rate of evaporation will depend on the size of the leak and on ambient conditions. As it evaporates, the cloud of gaseous hydrogen formed over the spill may move horizontally as it rises and dissipates. This hydrogen cloud may be cold enough to cause frostbite to exposed skin and should be avoided. While diesel fuel and gasoline leaks are easily visible and accompanied by a strong characteristic smell, gaseous hydrogen leaks are invisible and odorless. The only indication of a gaseous hydrogen leak may be a whistling noise similar to escape of other high-pressure gases. A liquid hydrogen leak may be accompanied by an area of fog surrounding the leaking hydrogen and/or the formation of frost on the tank or lines in the vicinity of the leak, because the super cold hydrogen cools the surrounding air and causes water vapor to condense. Based on hydrogen’s chemical and physical properties, there are a number of general principles that govern safe design and use of hydrogen fuel. These are essentially the same principles that apply to the use of any gaseous fuel (e.g., natural gas), but their application may be slightly different based on the properties of hydrogen. vii viii The most important safety principle in any situation is education—making anyone who will come into contact with a vehicle aware of a potential hazard. For hydrogen and other alternativefueled vehicles, this is done with appropriate labeling to let users, emergency responders, and the public know that hydrogen is present. As with other motor fuels, fire and explosions are the most significant everyday hazards associated with hydrogen. Also as with other fuels, a hydrogen leak from a vehicle’s fuel or engine system, or from a fueling station, provides the starting point for all fire and explosion hazards. Safe design for using hydrogen, both for vehicles and for fuel stations and buildings, therefore, requires attention to these safety principles: • Properly label all vehicles that use hydrogen fuel. • Avoid fire and explosion by: – Avoiding leaks through proper design and maintenance, – Providing leak detection systems to detect leaks and, if a leak is detected, shut off the fuel system as soon as possible, – Removing ignition sources from areas where leaked hydrogen might be present, and – Properly ventilating all enclosed spaces where leaked hydrogen might accumulate. These general principles translate into specific design and operating requirements for hydrogenfueled vehicles, the facilities that will house or maintain them, and hydrogen fuel stations. In most aspects, commercial vehicles powered by hydrogen will be identical to those powered by diesel fuel, but some hydrogen-specific design elements are required. Likewise, operation of these vehicles will be similar to operation of diesel-fueled vehicles, with a few exceptions. Each vehicle manufacturer will develop their own designs, which are likely to vary significantly in the details, while adhering to the same general design principles noted above. 1. INTRODUCTION 1.1 BACKGROUND Today, virtually all commercial trucks are powered by diesel fuel, while private cars are fueled by gasoline. While these petroleum-based fossil fuels have served society well for many years, their supply is limited, and their use creates pollution that contributes to poor air quality in many areas. Supported by our National Energy Policy, a new generation of technologies is currently being developed that allow the use of hydrogen as a fuel to power cars and trucks (see Table 1). In the future, hydrogen may be used in one of three ways to power vehicles: • To produce electricity in a fuel cell, • As a replacement for gasoline or diesel fuel in an internal combustion engine, or • As a supplement to gasoline or diesel fuel used in an internal combustion engine. Table 1. Why Hydrogen? 1 To reduce harmful pollution from vehicle exhaust To reduce carbon dioxide (CO2) emissions, which contribute to global warming 2 3 To reduce our growing dependence on foreign oil This document was developed by the Federal Motor Carrier Safety Administration as a reference for commercial vehicle fleet owners and operators who use hydrogen fuel in their vehicles, and it primarily focuses on safety. All motor fuels, including diesel fuel, gasoline, and natural gas pose risks of fire and explosion if handled improperly. Hydrogen is no different. While there are risks, hydrogen can be as safe, or safer, than diesel and other fuels when vehicles and fuel stations are designed and operated properly. While safe, hydrogen is different from other motor fuels, it has significantly different physical and chemical properties that affect how it must be safely stored and handled. Therefore, this document was designed to provide basic information about hydrogen properties and characteristics, as well as an overview of the vehicle systems than might use hydrogen fuel. It also provides basic guidelines for how vehicles, as well as fuel stations and maintenance facilities, should be designed and operated if hydrogen will be used. This information is provided so that fleet owners and operators will know what to look for—and what to do and not do—when using hydrogen fuel for their vehicles. 1 1.2 HYDROGEN USE AS A MOTOR FUEL There are several ways that hydrogen can be used as a motor fuel. It can be used to directly replace gasoline or diesel fuel in specially designed internal combustion engines (ICEs), or it can be used to supplement these typical fuels in existing engines. In either of these cases, the vehicle drive system will be identical to those used on most gasoline-powered or diesel-powered vehicles. The engine will drive the vehicle’s wheels through a transmission, drive shaft, and front or rear axle. Hydrogen can also be used as the fuel source for a “fuel cell engine,” in which case the vehicle’s drive system will be very different. A fuel cell directly creates electricity, which can be used to power an electric motor to drive the vehicle’s wheels. A fuel cell vehicle is, therefore, an electric vehicle, but one that creates its own electricity and does not need to be plugged in to recharge batteries. A small fuel cell can also be used to create electricity to directly power the auxiliary systems on a commercial truck (for example heating, air conditioning, and lighting in a sleeper berth), which are typically powered by the truck’s main engine. Using such a fuel cell auxiliary power unit (APU) would allow the driver to shut off the truck’s main diesel engine while resting, saving fuel and reducing pollution. Regardless of whether the hydrogen will be used in a fuel cell main engine, a fuel cell APU, or an internal combustion engine, there are different ways that it can be stored on the vehicle. As described below, these different storage technologies can introduce significantly different potential hazards, including very high pressure (gaseous hydrogen storage), very low temperature (liquid hydrogen storage), or high temperature (liquid fuel reforming) (see Table 2). Currently both fuel cells and hydrogen ICEs are in the early stages of commercialization. All of the major auto companies have fielded concept, prototype, or demonstration fuel cell sedans and sport utility vehicles in the last several years, with at least fifteen different models introduced since 2000 (Barnitt and Eudy, 2005; USFCC, 2006). Most of these vehicles have been operated by the companies themselves or have been fielded to government agencies and fleet customers as part of technology development or demonstration programs. The California Fuel Cell Partnership reports that its members have placed 134 light-duty fuel cell vehicles in service in California since 2000 (CAFCP, n.d.). In addition, there are currently nine fuel cell transit buses in service in the United States and Canada, and over 20 in Europe and Asia (Chandler and Eudy, 2006). It is expected that commercial fuel cells will be introduced into government and transit bus fleets between 2010 and 2020, with sales to commercial vehicle fleets and the public sometime between 2020 and 2030 (DOE, 2002). It is also expected that the first use of hydrogen fuel in the commercial truck sector will be to power fuel cell APUs rather than to power fuel cell or hydrogen ICE main propulsion engines. At least one company has announced plans to introduce commercial fuel cell APUs as early as 2011 (Delphi, 2005). Most current prototype fuel cell vehicles carry their hydrogen fuel as a compressed gas, and it is expected that this will continue to be the case for the earliest commercial vehicles. It may be desirable to store liquid hydrogen onboard a commercial vehicle because it has a higher energy density and would increase the range between fill-ups. However, onboard liquid hydrogen storage is more costly, and it is more likely that liquid hydrogen will be stored at fueling stations 2 to supply gaseous hydrogen to vehicles. Other storage technologies, such as metal and chemical hydrides, are much further from commercial readiness (DOE, n.d.). Several fuel cell buses have been demonstrated that “reform,” or extract hydrogen from, liquid methanol onboard (Georgetown University, 2003), and there are fuel cell APU systems under development that will derive their hydrogen from onboard reforming of diesel fuel or gasoline (Delphi, 2005). In addition, there are several commercial “hydrogen injection” systems available for retrofit on diesel engines (CHEC, n.d.). These systems produce small amounts of hydrogen by electrolysis of water carried on the vehicle, which is injected into the diesel engine along with the diesel fuel. Table 2. Challenges of Using Hydrogen 1 Because hydrogen is normally gaseous, fueling requires very high-pressure compression and large, expensive, onboard vehicle storage systems. 2 A supply of hydrogen and a network of fuel stations must still be developed. The remainder of this chapter provides a brief overview of the types of systems that might be found on a vehicle to store or use hydrogen fuel. 1.2.1 Hydrogen Fuel Cell Engines Fuel cells are often compared to both internal combustion engines (ICEs) and batteries and, in fact, they share some characteristics with each. All three types of devices are used to transform one type of energy into another. A diesel engine turns chemical energy contained in diesel fuel into heat energy through combustion with oxygen from the air, and then turns that heat energy into mechanical energy, turning the vehicle’s wheels through a transmission and drive shaft. On the other hand, a battery is a galvanic cell; it uses reactions between chemicals stored inside to turn chemical energy directly into electricity, which can then be used to power a number of devices, including an electric motor to produce mechanical energy. Like a diesel engine, a fuel cell requires fuel (hydrogen) and oxygen (air). However, like a battery, it is capable of directly producing electricity. A fuel cell is also a galvanic cell; the hydrogen and oxygen do not combust inside the device. Instead, the hydrogen and oxygen react electrochemically and produce electricity. See Table 3 for a comparison of the major differences between fuel cells and ICEs and batteries. 3 Table 3. Comparison of Fuel Cells to ICEs and Batteries Internal Combustion Engine (ICE) Battery Fuel Cell Engine Similarities to: • Both are supplied with air and a hydrogen-rich fuel. • Both have similar mechanical support systems (fuel system, air system, cooling system). • Both are galvanic cells that directly generate electricity through electrochemical reactions. • Both have an anode and a cathode in contact with an electrolyte. • With both, individual low-voltage DC cells are combined in series to attain higher voltage and power. Fuel Cell Engine Differences from: • In a fuel cell, hydrogen reacts with oxygen electrochemically not by combusting as in an ICE. • A fuel cell directly generates electricity not mechanical energy. • A fuel cell does not produce harmful tail pipe emissions or CO2. • A fuel cell does not need to be recharged like a battery; it is refueled by the H2 and O2. • In a fuel cell, the anode and cathode are gases (H2 and O2); while in a battery, they are metal. As with a battery, the electricity produced by a fuel cell can be used to power any number of devices. In the case of a vehicle, it is most often used to power an electric motor to move the vehicle down the road. A fuel cell vehicle is, therefore, an electric vehicle, powered by an electric motor. Fuel cells have been around for a long time and have been used in the United States space program since the 1960s (College of the Desert, 2001c). It has only been in the last few years, however, that they have been developed for use in conventional vehicles. There are a number of different fuel cell technologies that employ different chemical reactions to combine hydrogen and oxygen to produce electricity. The most common technology used in vehicles is called a Proton Exchange Membrane (PEM) fuel cell. See Figure 1, which shows the layout and operation of a PEM fuel cell. Also see Appendix A for a more in-depth description of the construction of a PEM fuel cell and the chemical reactions that take place in the cell. 4 e- eeeFuel In Excess Fuel Electrical Current Water and Heat Out Air In H+ H+ H+ H+ H2 H2O O2 Anode Electrolyte Cathode e- eeeFuel In Excess Fuel Electrical Current Water and Heat Out Air In H+ H+ H+ H+ H2 H2O O2 Anode Electrolyte Cathode Figure 1. Operation of a Proton Exchange Membrane Fuel Cell Source: DOE, 2006. The maximum voltage that one PEM “cell” can produce is 1.2 VDC, but the actual voltage depends on how much current is being drawn from the cell. The cell can put out the greatest amount of power at between 0.5 and 0.6 volts, so that is where they are generally designed to operate. To create a device powerful enough to power a large vehicle, up to 1,200 cells are connected in series, to produce a peak power of 100 kW or more at between 300 and 600 VDC (nominal). Physically the individual PEM cells are usually stacked together, separated by a cooling plate between each set of cells. These cooling plates circulate a mixture of water and ethylene glycol to remove excess heat created during operation of the cells. These cooling plates are part of a cooling system that is similar in both design and function to the cooling systems used with diesel engines. A collection of individual fuel cells used to create a practical device is usually referred to as a fuel cell “stack” (see Figure 2). Figure 2. PEM Fuel Cell Stack Source: DOE, 2006. 5 The fuel cell stack must be supported by a number of auxiliary systems that together make up the “fuel cell engine.” In addition to a cooling system, the fuel cell engine needs a fuel system, an air system, and a water management system. See Figure 3 for a generic schematic of a PEM fuel cell engine. In a PEM fuel cell, engine hydrogen and air are saturated with water and fed into the fuel cell stack. Inside each PEM cell, the hydrogen and air react with each other across a thin plasticlike film, called a proton exchange membrane, but they never mix. Electricity is produced by each cell, and water and a small amount of heat are the only by-products. Excess water not needed to humidify the gases is exhausted, with air, out the tailpipe. Air System H2 Fuel Storage System H2 Fuel Delivery System H2 Humidification System Fuel Cell Stack Water Recovery System Exhaust Air Air H2 H2 H2 H2 H2o H2o H2o H2o Air Humidification System Air System H2 Fuel Storage System H2 Fuel Delivery System H2 Humidification System Fuel Cell Stack Water Recovery System Exhaust Air Air H2o H2o H2o H2o Air Humidification System H2 H2 H2 H2 Figure 3. Generic PEM Fuel Cell Engine Schematic PEM fuel cells generally operate at relatively low temperatures (140 to 180 ºF) and pressures (from 0 to 15 psig). The exact layout and details of a fuel cell engine and its subsystems will depend on the specifics of the design and its specified operating parameters. Packaging and layout of the fuel cell engine in the vehicle can also vary significantly. See Figure 4 for a photo of a fuel cell engine and electric drive motor that was installed in a transit bus. 6 Figure 4. PEM Fuel Cell Engine and Electric Drive Motor for a Transit Bus Photo courtesy of AC Transit. PEM fuel cell engines fueled by hydrogen produce virtually none of the volatile organic hydrocarbon or nitrogen oxide tailpipe emissions that come from combustion of fuel in gasoline and diesel engines, and which together produce ground-level ozone, or “smog” in the atmosphere in the presence of sunlight. They also produce virtually none of the harmful particulate emissions produced by diesel engines and zero carbon dioxide emissions. Carbon dioxide is a major byproduct of fuel combustion in diesel and gasoline engines. As a so-called “greenhouse gas,” carbon dioxide is a contributor to global warming. In addition to reduced exhaust emissions, the potential benefits of using hydrogen fuel cells to power commercial vehicles include lower total energy use due to improved efficiency of the fuel cell compared to an internal combustion engine. The actual “wells-to-wheels” efficiency of a fuel cell vehicle will depend on how the system is designed, as well as how the hydrogen fuel is produced. Many fuel cell vehicles are designed with a hybrid propulsion system that incorporates a large battery to supplement the fuel cell. The battery provides power during acceleration, allowing the fuel cell to be smaller. It is also used to capture energy that is normally wasted in braking, which can later be re-used, increasing net efficiency, especially in stop-and-go city driving. See Figure 5 for a comparison of “wells-to-wheels” fuel use (liters per mile)2 for vehicles with different types of power sources. This figure is illustrative only and does not include all potential combinations of fuel and propulsion technology. 2 One liter per mile is equivalent to 0.26 gal/mile. 7 Figure 5. Wells-to-Wheels Fuel Use for Different Propulsion Systems Source: ADL-DOE Fuel Choice for Fuel Cell Vehicles Study Results, February 2002. Usually pure hydrogen is used to fuel a PEM fuel cell engine. While a mixture of hydrogen and carbon dioxide can be used, other “contaminants” must be kept to a minimum in the fuel supplied to the cells, especially carbon monoxide (CO) and sulfur. Both CO and sulfur can reduce the activity of the platinum catalysts used in the PEM cells, reducing the amount of power that the cells can produce (EG&G, 2004). 1.2.1.1 Solid Oxide Fuel Cell APUs Like PEM fuel cells, solid oxide fuel cells (SOFCs) are galvanic cells that directly produce electricity from hydrogen and oxygen through an electrochemical reaction. However, SOFCs are constructed of different materials and use a different chemical reaction from PEM fuel cells. SOFCs operate at much higher temperatures than PEM fuel cells – between 1,100 °F and 1,800 °F. When combined with a small fuel reformer they can also use diesel fuel or gasoline vapors as fuel, eliminating the need to carry hydrogen gas onboard. In an SOFC, the electrolyte is not a plastic-like material as it is in a PEM cell; it is a ceramic material made of a solid metal oxide, usually zirconia oxide. This electrolyte does not need to be coated with an expensive platinum catalyst as in a PEM cell. As with a PEM fuel cell, the major by-products of the reactions inside the cell are electricity, water, and heat. See Figure 6. Also see Appendix A for a more detailed description of the construction of SOFCs and the chemical reactions that take place inside the cells. 8 e- e- e- e- Fuel In Air In Unused Gases Out Anode Electrolyte Cathode Excess Fuel and Water H2 O2 H2O O= O= e- e- e- e- Fuel In Air In Unused Gases Out Anode Electrolyte Cathode Excess Fuel and Water H2 O2 H2O O= O= Figure 6. Operation of an SOFC Fuel Cell Source: DOE, 2006. Unlike a PEM cell, an SOFC does not need to be fueled with pure hydrogen gas. Because SOFCs operate at such high temperature and because oxygen ions are transferred through a solid oxide electrolyte material—not hydrogen ions—SOFCs support automatic “reforming” of gaseous hydrocarbon fuels like methane (natural gas) within the device. Reforming is the chemical process of separating the hydrogen from the carbon atoms in a hydrocarbon fuel (see Section 1.4). Diesel fuel and gasoline vapors can not be internally reformed by an SOFC, but can be used to fuel an SOFC if it is combined with a relatively simple fuel reformer/processor. When using diesel fuel, the “reformate” produced by the fuel processor and introduced as the fuel at the anode of the SOFC will include hydrogen, nitrogen, carbon monoxide, and CO2. The exhaust from the SOFC will also include CO2 and nitrogen, as well as water and waste heat. SOFCs operate at much higher temperatures than PEM fuel cells—between 1,100°F and 1,800°F—so the waste heat created during operation is also at a higher temperature and can, therefore, more easily be put to use, for example, to heat the interior of a vehicle as is typical of the waste heat from an ICE. There are at least fifteen companies that have demonstrated prototype or commercial SOFC systems (HARC, 2004). Most of these systems are small, producing from 200 watts to 25 kilowatts of power. Several manufacturers are developing low-power systems specifically for use as an auxiliary power unit (APU) on commercial trucks (DELPHI, 2005) Truck APUs are used to provide electrical power and sometimes heat to power truck accessories such as cabin lighting, air conditioning, and heating. Most often used with sleeper berthequipped, truck-tractors they allow these loads, which are normally supplied by the truck’s main engine, to be supplied even when the main engine is off. 9 Without an APU, many long-haul truckers end up idling their main engines for eight hours a day or more while resting in the sleeper-berth. This practice is wasteful and results in unnecessary harmful exhaust emissions. Testing by the U.S. Environmental Protection Agency has shown that a commercial truck’s main engine typically consumes about one gallon of fuel per hour while idling, while a properly sized ICE APU will burn only about one fifth as much (EPA, 2002). The use of an APU instead of main engine idling can therefore save a truck operator money and reduce pollution at the same time. In comparison to an ICE APU, an SOFC APU could be more efficient, smaller and lighter, quieter, and produce fewer exhaust emissions (DELPHI, 2005). Because an SOFC with a fuel processor can be fueled directly with diesel fuel, there would be no need to carry compressed hydrogen on the vehicle (see Section 1.4). 1.2.2 Hydrogen Internal Combustion Engines Theoretically any typical spark-ignited engine, like the gasoline engines used in most cars, can operate on a range of liquid or gaseous fuels, including hydrogen. However, due to differences in the chemical properties of the various fuels, the designs of engines optimized for each are quite different. Because of the wide flammability range of hydrogen, an internal combustion engine (ICE) operating on hydrogen can operate with a much leaner air/fuel mixture than a typical gasoline engine, which improves efficiency. A hydrogen ICE developed by Ford Motor Company can operate with an air fuel ratio as high as 86:1, compared to 14.7:1 for typical gasoline engines (see Figure 7). This results in about a 25 percent improvement in efficiency (NEW-CARS, 2003). Because hydrogen is a light gas, it displaces more volume in the combustion chamber than gasoline vapors, and super-charging is generally required to get equivalent power output as the same sized gasoline engine. Other design changes compared to typical gasoline engines may be required to reduce the possibility of pre-ignition, or knock, because of hydrogen’s low ignition energy. These may include the use of a disk-shaped combustion chamber to reduce turbulence in the cylinder, the use of more than one spark-plug, and the use of multiple exhaust valves (College of the Desert, 2001b). Figure 7. Ford V10 Hydrogen Engine Photo courtesy of Ford Motor Company. 10 Besides the potential for better fuel economy because of improved efficiency, hydrogen ICEs offer other advantages over gasoline and diesel engines, including reduced exhaust emissions. Because there is no carbon in the fuel, a vehicle powered by a hydrogen ICE would have zero emissions of the greenhouse gas CO2. Tailpipe emissions of nitrogen oxides and volatile organic hydrocarbons would also be lower. Typically the hydrogen fuel for a hydrogen ICE is carried on the vehicle as a high-pressure compressed gas (see Section 1.3 for a description of hydrogen storage systems). In addition to Ford, at least two other companies have developed hydrogen ICEs for cars, either as prototypes or commercial products (CHHN, 2004). There are also fourteen buses currently operating in Berlin, Germany, and one in Thousand Palms, California, which are powered by heavy-duty hydrogen ICEs (Chandler and Eudy, 2006). 1.2.3 Hydrogen Injection Systems A hydrogen injection system for a diesel engine produces small amounts of hydrogen and oxygen on demand by electrolyzing water carried onboard the vehicle. The electricity required is supplied by the engine’s alternator or 12/24-volt electrical system (see Section 1.5 for a description of electrolysis). The hydrogen and oxygen are injected into the engine’s air intake manifold, where they mix with the intake air. In theory, the combustion properties of the hydrogen result in more complete combustion of diesel fuel in the engine, reducing tailpipe emissions and improving fuel economy (CHEC, n.d.). Limited laboratory testing of a hydrogen injection system installed on an older diesel truck engine operated at a series of constant speeds showed a 4 percent reduction in fuel use and a 7 percent reduction in particulate emissions with the system on (ETVC, 2005). A hydrogen injection system for a diesel engine produces and uses significantly less hydrogen than a hydrogen fuel cell or hydrogen ICE, and does not require that compressed or liquid hydrogen be carried on the vehicle. The system is designed to produce hydrogen only when required, in response to driver throttle commands. When the system is shut-off, no hydrogen is present on the vehicle. 1.3 HYDROGEN STORAGE ON VEHICLES A sufficient amount of hydrogen to provide satisfactory driving range must be stored onboard a hydrogen-powered vehicle. This is a significant challenge because, at normal temperature and pressure, a given volume of hydrogen is very light and contains very little energy. Hydrogen vehicle fuel storage systems on commercial vehicles are larger, heavier, and more expensive than diesel vehicle fuel storage systems. Given the limitations of onboard hydrogen storage, hydrogen-powered commercial vehicles may not provide comparable operating range to typical diesel-powered commercial vehicles. 11 There are five ways that the hydrogen can be stored on the vehicle: • As a high-pressure gas, • As a very low temperature liquid, • Chemically bound or physically absorbed onto a material such as a solid “hydride,” As a component of a liquid hydrocarbon fuel (which is reformed), or • As a component of water (H20) (which is hydrolyzed). Currently the most common method of onboard hydrogen storage for vehicles powered by fuel cells and hydrogen ICEs is as a compressed gas. This is likely to continue to be true for the foreseeable future. 1.3.1 Compressed Hydrogen Storage When stored as a gas, hydrogen can be fed directly into a fuel cell or ICE without further processing. However, like all gases hydrogen is difficult to compress. In order to get enough fuel onto a vehicle to be able to go several hundred miles between fill-ups, but without taking up too much space, the hydrogen must be stored at very high pressure. Most current vehicle systems store hydrogen at a pressure of 5,000 pounds per square inch (psi). In the future, hydrogen storage pressures may be as high as 10,000 psi (DOE, n.d.). Even at these pressures, a gaseous hydrogen storage system will be much larger and heavier than the diesel fuel tanks on current trucks. Hydrogen with the same amount of energy as 100 gallons of diesel fuel, if stored at 5,000 psi, would take up over twelve times as much space—over 170 cubic feet. Because high-pressure storage tanks must be very strong to contain the pressure, the total weight of such a system when full would be over 2,500 pounds—almost four times more than the weight of a full 100 gallon diesel tank (College of the Desert, 2001a). In a diesel tank, the weight of the fuel would be over 90 percent of the total, while in a gaseous hydrogen storage system, the opposite is true—the weight of the hydrogen fuel would only be 10 percent of the total, with the remaining 90 percent the weight of the tank. High-pressure storage cylinders can be made of metal (steel or aluminum) or they can be made with a thin metal or plastic liner that holds the gas, covered with a composite overwrap that provides most of the strength. The designs for these cylinders are subjected to rigorous qualification tests to ensure that they can withstand the forces that they might be subjected to in service on a vehicle, including in a crash. Hydrogen storage systems for commercial vehicles will likely be composed of multiple storage cylinders connected to a common manifold. See Figure 8, which shows an automotive hydrogen fuel storage system that includes two high-pressure storage cylinders. Systems composed of more than one storage cylinder will normally include a manual isolation valve for each cylinder that can be used during servicing, as well as one or more electrically activated valves that can be used to automatically isolate the fuel supply in the case of a leak or other system problem. 12 Figure 8. Gaseous Hydrogen Storage System Source: DOE. All high-pressure hydrogen storage cylinders must also be equipped with a pressure relief device (PRD) and/or a thermal relief device (TRD) to protect against cylinder rupture if the pressure inside the cylinder gets too high. A PRD includes a metal disk designed to rupture at a set pressure, releasing the gas inside the cylinder (Air Products, 2004). The most likely reason for overpressure in a hydrogen fuel cylinder is a vehicle fire. If engulfed in flames, the pressure inside the tank will rise as the temperature rises. TRDs are, therefore, made with a plug of fusible metal that begins to melt and deform at a set temperature (Air Products, 2004). As the plug deforms, it can no longer hold the pressure inside the cylinder and gas escapes. Some devices combine both a rupture disk and a fusible plug. PRDs and TRDs are not pressure relief valves (see Section 1.3.2). Once the disc ruptures or the fusible plug melts, all of the gas in the cylinder escapes, and they cannot be reset; they must be replaced. Typically, the outlets from all PRD/TRDs are run into a common manifold that exits the vehicle at or near the roof line to ensure that any escaping gas is directed upward away from vehicle occupants or pedestrians. Fueling with compressed hydrogen is similar to fueling with other high-pressure gases, such as compressed natural gas (CNG). The on-vehicle fueling ports and fueling nozzles used are very similar to those used with CNG, though they are designed to operate at higher pressures.3 1.3.2 Liquid Hydrogen Storage Very few fuel cell or hydrogen ICE vehicles have been deployed with onboard liquid hydrogen storage. Liquid hydrogen storage systems are smaller and lighter than comparable compressed hydrogen storage systems, but are more complex and expensive and have other disadvantages. Bulk liquid hydrogen storage systems are more commonly used at centralized vehicle fueling stations. The boiling point of hydrogen at atmospheric pressure is –423°F; above that temperature hydrogen exists as a gas, and it will only liquefy if the temperature drops below the boiling point. Compressors and heat exchangers can be used to lower the temperature of hydrogen gas to produce liquid hydrogen, which must then be kept at this very low temperature or it will “boil 3 The maximum pressure for fuel systems on typical heavy-duty CNG vehicles is 3,600 psi. 13 off” again as a gas. To maintain its temperature, liquid hydrogen is stored in specialized, heavily insulated, containers called “dewars,” “cryotanks,” or “cryogenic vessels.” A typical cryogenic container is made of metal and is double-walled. The inner tank is wrapped in multiple insulating layers and is enclosed by the second outer metal tank. Air is removed from the space between tank walls to create a vacuum. This design minimizes heat transfer by radiation, convection. or conduction. Even the best cryotanks allow some heat through the tank walls. As the liquid hydrogen inside absorbs the heat, some of it evaporates, raising the tank pressure. Cryotanks are generally designed to operate near atmospheric pressure and are not designed to hold high pressures. Therefore, as tank pressure rises, some gaseous hydrogen must be vented to relieve the pressure. All cryotanks are equipped with pressure relief safety valves for gas venting. In a pressure relief valve, a spring holds a plunger against the valve opening with a specific amount of pressure. When the pressure inside the tank rises above the spring pressure, the plunger moves back against the spring and the valve opens, releasing some gas. As gas vents, the pressure inside the tank falls. When the pressure falls enough, the spring pushes the plunger back against the valve opening, closing the valve. Pressure relief valves are different from PRD/TRDs (see Section 1.3.1) because they are designed to open and close numerous times during their life, and to vent only part of the tank contents each time they open. The amount of venting from an on-vehicle liquid hydrogen storage system will depend on the design of the system, the ambient temperature, and how often the vehicle is used. Many of the cryogenic tanks currently in use for bulk storage and delivery can store liquid hydrogen for a week or more without any venting loss (Linde, n.d.). Nonetheless, vehicle storage facilities and maintenance operating plans need to account for the possibility of hydrogen venting, particularly from vehicles parked indoors for long term. See Figure 9 for an illustration of a liquid hydrogen fuel system for a vehicle. In addition to the super-insulated cryotank, a typical on-vehicle liquid hydrogen storage system will include a filling port, a safety (pressure relief) valve, and a heat exchanger. The safety valve is connected to a line or plenum, which directs vented hydrogen gas through a diffuser out of the top of the vehicle. Inside the tank, there is a filling line, a gas extraction line, a liquid extraction line, one or more level probes, and an electric heater. The heater is used to raise the pressure inside the tank to force out hydrogen gas in response to fuel demand. Mounting hardware holds the tank securely to the vehicle. 14 Figure 9. Liquid Hydrogen Fuel System Source: DOE. The gas released from the liquid hydrogen storage tank is extremely cold. Before entering the fuel cell or hydrogen ICE fuel delivery system, the gas passes through the heat exchanger, which raises the temperature. Typically the heat exchanger is connected to the same cooling system used to control the fuel cell stack or ICE temperature. Once through the heat exchanger, the hydrogen is close to the operating temperature of the fuel cell stack or ICE. In the past, some fueling couplings used with liquid hydrogen required heating and rinsing to separate the two parts and to disconnect them from the vehicle after fueling. Newer designs have improved the safety and speed of fueling operations through the use of a special coaxial “cold withdrawal coupling.” This allows the operator to immediately disconnect from the vehicle after refueling has stopped and to rapidly refuel multiple vehicles without waiting for the coupling to warm up in between (Linde, n.d.). The fueling operation used with liquid hydrogen is similar to fueling with compressed hydrogen. The connection between the vehicle and the fuel station is manual. To fuel, the operator inserts the male part of the coupling from the fuel station into the female part of the coupling on the vehicle. When a positive connection is made, the operator turns a lever to lock the coupling and fuel starts to flow (see Figure 10). 15 Figure 10. Liquid Hydrogen Fueling There is a data connection in the fuel coupling connected to the vehicle’s control system. Using signals from the probes inside the storage tank, the vehicle signals the fuel station when the tank is full. After the liquid hydrogen has stopped flowing, the operator unlocks the coupling and removes it. On-vehicle liquid hydrogen storage systems will be larger than the diesel fuel tanks on current trucks, but smaller than compressed hydrogen storage systems. Liquid hydrogen with the same amount of energy as 100 gallons of diesel fuel would take up four times as much space as the diesel fuel, but less than one third as much space as the same amount of gaseous hydrogen stored at 5,000 psi. The weight of the liquid hydrogen storage system would be about 50 percent greater than the weight of the diesel fuel system when full, but less than half the weight of the compressed hydrogen fuel system (College of the Desert, 2001a). As with compressed hydrogen storage, the weight of the containment vessel for liquid hydrogen accounts for the majority of the total weight of the system. The size and weight advantage of liquid hydrogen storage compared to compressed hydrogen storage is balanced by higher cost and complexity of the storage system, the energy required to liquefy the hydrogen, and ongoing hydrogen venting. Given these disadvantages, to date very few fuel cell or hydrogen ICE vehicles have been deployed with onboard liquid hydrogen storage. Bulk liquid hydrogen storage at a centralized vehicle fueling station is much more common. Bulk liquid hydrogen storage tanks have similar construction to onboard vehicle storage tanks. 1.3.3 Hydrogen Storage in Materials There are a number of other ways to store hydrogen in solid or liquid materials, for release on demand. The two most studied approaches are adsorption of hydrogen into solid metal hydrides and “chemical” storage as part of a chemical hydride. Both of these approaches are inherently safer than storing hydrogen as a high-pressure gas or a cryogenic liquid, and the process of releasing the hydrogen from the storage medium is less complex than reforming of hydrocarbon 16 fuels. At present, these systems are heavy and bulky and require further development to be practical. Metal hydride storage systems are based on the fact that some metals can adsorb significant amounts of hydrogen under high pressure and moderate temperatures. The hydrogen is either adsorbed onto the surface of the metal or actually incorporated into the crystalline lattice of the solid metal. When heated to some higher temperature at low pressure, the hydrogen is released from the metal. In a vehicle hydrogen storage system, waste heat from the fuel cell or ICE engine would typically be used to release the hydrogen (DOE, n.d.). Such a system could potentially be “re-fueled” onboard the vehicle by connecting it to a high-pressure hydrogen source. Chemical hydrides are compounds that include significant numbers of hydrogen atoms chemically bound to other types of atoms, for example, sodium borohydride, which is composed of one sodium atom, one boron atom, and four hydrogen atoms (NaBH4). In a hydrogen storage system based on a chemical hydride, the hydrogen is released on demand through a chemical reaction with either water or an alcohol. The solid hydride is made into a slurry with an inert liquid, and when hydrogen is required, water is added, releasing hydrogen (DOE, n.d.). Unlike metal hydrides, chemical hydrides cannot be regenerated on the vehicle; after releasing all of its hydrogen the spent slurry must be removed and regenerated off-site. Current metal and chemical hydride fuel storage systems are heavy and bulky; they can only store and release 6 percent or less of their weight as hydrogen (DOE, n.d.) (i.e., only 6 percent of the total weight of the system is the hydrogen fuel; the rest of the weight is the container). These systems have even lower energy densities than compressed gaseous hydrogen storage systems. More work is required to develop truly practical storage systems for vehicles based on these technologies. 1.4 REFORMING OF LIQUID FUELS All liquid hydrocarbon fuels (gasoline, diesel fuel, kerosene, and methanol), as well as natural gas, contain significant hydrogen, which is chemically bound to carbon. Both diesel fuel and gasoline contain about two hydrogen atoms for every carbon atom, while natural gas contains four. “Reforming” of a hydrocarbon fuel is a chemical process that converts the natural gas or liquid fuel into a hydrogen-rich gas. The product of this process is called “reformate,” and when used to fuel a PEM fuel cell, it is typically composed of a mixture of hydrogen gas, carbon dioxide, nitrogen, and water vapor. Reformate used to fuel an SOFC can also contain carbon monoxide. Depending on the fuel being reformed and the process used, the reformate could be anywhere from 40 to 75 percent hydrogen by volume (College of the Desert, 2001a). There are a number of processes that can be used to reform different fuels. Fuel reforming often requires several different steps, each of which involves flowing the fuel or partially processed reformate across a catalyst bed in a closed vessel, or “reactor.” These reactors are generally constructed like heat exchangers. with the working fluid flowing through one set of channels coated with some kind of a catalyst, and another fluid (thermal oil or water-ethylene glycol) 17 flowing through another set of channels to either add or take away heat. Each process step may also require the addition of air or water to the inlet flow stream. The catalyst coating promotes chemical reactions in the vessel, which usually occur at relatively high temperatures and pressures. The necessary process heat may be produced by combusting some of the liquid fuel and/or depleted reformate after it leaves the fuel cell stack, in a burner. As a whole, the fuel reformer unit is close to being a “solid state” device, with very few moving parts. Natural gas and alcohol fuels, like methanol, are easier to reform than gasoline or diesel fuel and also yield a reformate with higher hydrogen content. Both gasoline and diesel fuel are a mixture of different hydrocarbons, including aromatics and olefins that tend to form polymer gums and carbon during reforming, which can block the reformer catalyst sites (College of the Desert 2001a). Reforming of gasoline and diesel fuel, especially for use in a PEM fuel cell, usually requires additional processing steps. Hydrogen is often produced at a centralized hydrogen fueling station by reforming natural gas on site. If so, additional processing steps are used to remove the carbon dioxide and other impurities from the reformate to produce very pure hydrogen gas. This hydrogen is then compressed for onsite storage and delivery to vehicles. Different reformer designs are possible, but most will likely be packaged into a “hot box” that incorporates all of the process steps, including the process heater or burner, into a relatively compact unit housed in a single enclosure (see Figure 11). The plumbing inside this box may be very complicated, with the different systems feeding each other. The device will likely also have interconnections with the fuel cell stack outlet (for depleted reformate), the fuel cell water recovery system, the fuel cell cooling system, and the liquid fuel storage system. The reformate leaving the fuel reformer is generally at approximately the same temperature and pressure at which the fuel cell stacks operate. For SOFC APUs, the fuel reformer and SOFC stacks may be packaged into a single unit in a common enclosure, with only external fuel line, process air intake, exhaust outlet, and electrical connections to other vehicle systems. Onboard reformers can also be used with fuel cell vehicles so that compressed or liquid hydrogen does not need to be carried on the vehicle. For example, Georgetown University has fielded a fuel cell transit bus operated on methanol fuel that is reformed onboard. The methanol fuel processor on this bus uses low temperature steam reformation and selective oxidation to make the hydrogen-rich reformate, which is fed to a PEM fuel cell. In steam reformation, the methanol must first be vaporized and mixed with steam. The steam/methanol mixture then passes across a heated catalyst bed in the steam reformer, which converts the methanol and water to hydrogen gas, carbon dioxide, and carbon monoxide. Because PEM fuel cells cannot tolerate carbon monoxide, the reformate must go through a second catalytic process called selective oxidation, which converts the carbon monoxide into carbon dioxide. The final reformate is approximately two-thirds hydrogen, with the balance CO2, water, nitrogen, and less than 20 parts per million CO. The required heat for the process is 18 provided by oxidizing the depleted reformate in a catalytic burner after it exhausts from the fuel cell stacks. See Figure 11 for a picture of this methanol fuel processor. Figure 11. Onboard Methanol Reformer for a Bus Photo courtesy of Georgetown University. At least two companies are also working on a fuel reformer/processor to reform diesel fuel to power an SOFC APU. Unlike a PEM fuel cell, an SOFC can tolerate CO, so this fuel processor is based on catalytic partial oxidation and does not require the second, selective oxidation processing step. Compared to onboard storage and use of compressed or liquid hydrogen in a PEM fuel cell engine or SOFC APU, onboard reforming of hydrocarbon fuels creates more tailpipe emissions. In particular, the vehicle will emit carbon dioxide, as well as small amounts of nitrogen oxides created during fuel reforming. 1.5 ELECTROLYSIS OF WATER The most abundant source of hydrogen on earth is water—every molecule of water contains one oxygen atom and two hydrogen atoms. It is relatively simple to separate the hydrogen in water from the oxygen using electricity to run an electrolyzer. An electrolyzer is a galvanic cell composed of an anode and a cathode submerged in a water-based electrolyte. In many ways, the operation of an electrolyzer is the opposite of operating a hydrogen fuel cell. In a fuel cell, hydrogen and oxygen are supplied to the anode and the cathode, and they combine to form water while creating an electrical current that can be put to use (see Section 1.2.1 and Appendix A). In an electrolyzer, an electrical current is applied between the anode and the cathode, which causes the water in the electrolyte to break down, releasing oxygen gas at the anode and hydrogen gas at the cathode (see Figure 12). 19 20 Water and an onboard electrolyzer cannot be used to power a fuel cell or hydrogen ICE vehicle because of the large amount of electricity required to operate the electrolyzer. An electrolyzer can be used at a centralized fueling station to produce hydrogen, which is then compressed for on-site storage and delivery to vehicles. For a centralized electrolyzer, the electrical energy could be supplied from the electrical grid or from a dedicated renewable source, such as a wind turbine or solar cell array. Figure 12. Electrolysis of Water to Produce Hydrogen and Oxygen Source: College of the Desert, 2001a. Onboard electrolyzers are used with hydrogen injection systems for diesel engines (see Section 3.5). In this case, only a small amount of hydrogen and oxygen are produced to supplement, not replace, the diesel fuel used in the engine. The electricity to operate the electrolyzer is typically supplied by the engine’s alternator or 12/24-VDC electrical system. 2. PROPERTIES OF HYDROGEN Hydrogen is the most abundant element in our universe. In addition to being a component of all living things hydrogen and oxygen together make up water, which covers 70 percent of the earth. In its pure form, a hydrogen molecule is composed of two hydrogen atoms (H2) and is a gas at normal temperatures and pressures. It is the lightest gas (even lighter than helium) with only 7 percent of the density of air. If you get it cold enough (–423°F), gaseous hydrogen will liquefy, and it can be transported and stored in this form. There is virtually no “free” hydrogen on earth; all of it is combined with other elements (mostly oxygen or carbon) in other substances. Every molecule of water contains two hydrogen atoms and one oxygen atom. Hydrocarbon fuels such as coal, gasoline, diesel, and natural gas also contain hydrogen. In the case of gasoline and diesel fuel, there are approximately two hydrogen atoms for every carbon atom, while natural gas contains four hydrogen atoms for every carbon atom. In order to directly use hydrogen as a fuel (whether in a fuel cell or in an internal combustion engine), it must be separated from these other elements. The hydrogen fuel used in vehicles is either derived from water (by electrolysis) or from a gaseous or liquid hydrocarbon fuel (by reforming). After being separated it must be stored—first at the fuel station and then on the vehicle. Some fuel stations include liquid hydrogen storage, but on the vehicle, hydrogen is usually stored as a gas at high pressure. It is also possible to store a liquid fuel (gasoline, diesel, and methanol) onboard a vehicle and then use an onboard reformer to separate the hydrogen just before it is used in the fuel cell engine. While this requires additional equipment on the vehicle, it removes the need for high-pressure gas storage. This chapter provides an overview of the properties of both gaseous and liquid hydrogen that are necessary to understand how hydrogen differs from more familiar motor fuels, such as gasoline and diesel fuel, and what is required to handle and use it safely. While there are risks, hydrogen can be as safe, or safer, than diesel and other fuels when vehicles and fuel stations are designed and operated properly. All fuels require particular design and handling practices based on their properties, and all present certain hazards when mishandled. Understanding the properties of hydrogen is necessary to understanding what is required to use it safely. Building on the discussion of hydrogen properties, this chapter also provides an overview of the general principles that govern safe design and use of hydrogen fuel. These principles inform the design and operating guidelines presented in chapters 3 through 5. 2.1 GASEOUS HYDROGEN Hydrogen gas is colorless, odorless, tasteless, and noncorrosive, and it is nontoxic to humans. It has the second widest flammability range in air of any gas, but leaking hydrogen rises and diffuses to a nonflammable mixture quickly. Hydrogen ignites very easily and burns hot, but 21 tends to burn out quickly. A hydrogen flame burns very cleanly, producing virtually no soot, which means that it is also virtually invisible. 2.1.1 Flammability, Ignition, and Luminosity A mixture of hydrogen and air will burn when there is as little as 4 percent hydrogen or as much as 75 percent hydrogen in the mix4 This is a very wide flammability range. In comparison diesel fuel vapors in air will burn over a range of 0.6 percent to 5.5 percent. With less than 0.6 percent diesel in the mixture it is too lean to ignite, and with more than 5.5 percent diesel in the mixture it is too rich. Natural gas will burn over a range of 5 percent to 15 percent. It takes very little energy to ignite a hydrogen-air mixture—a common static electric spark may be sufficient. As shown in Table 4, it takes less than one tenth of the energy to ignite a hydrogen air mixture as it does to ignite a mixture of gasoline vapors in air. Over much of its flammable range, common static electricity would be enough to ignite a hydrogen-air mixture. In some cases, the electrostatic charges or heating created by the flow of hydrogen from a leaking vessel would be enough to ignite the leaking hydrogen (Murphy, et al., 1995; Argonne, 2003). Table 4. Hydrogen Flammability Range and Ignition Energy Hydrogen Gasoline Diesel (#2 - Low Sulfur) Methane (CNG) Auto-ignition Temperature 932°F (500°C) 495°F (257°C) 480°F (250°C) 999°F (537°C) Ignition Energy in Air 0.02 mJ 0.24 mJ N/A N/A Flame Temperature in Air 4010°F (2045°C) 3987°F (2197°C) N/A 3484°F (1918°C) Lower Flammable Limit 4 percent 1.4 percent 0.6 percent 5 percent Upper Flammable Limit 74 percent 7.6 percent 5.5 percent 15 percent Buoyancy: Gas or Vapor Density Relative to air (at STP) 0.07 2 to 4 4 to 5 0.6 Boiling Point at 1 atm. –422°F (–252°C) 80 to 437°F (25 to 225°C) 350 to 650°F (180 to 345°C) –259°F (–162°C) Source: Data from Chemical Properties Handbook, edited by Yaws, C.L., 1999, McGraw-Hill. Hydrogen flames burn very cleanly, producing virtually no soot. It is the soot created by most fuel that makes a flame visible. In addition, much of the energy radiated by a hydrogen flame is in the ultraviolet range, rather than the infrared or visible ranges of the light spectrum. Therefore, a hydrogen flame is virtually invisible to the human eye in day light, though the energy being 4 At room temperature and one atmosphere pressure. 22 released by the flame may create a visible “shimmer” in surrounding air due to changes in the air density. At night, hydrogen flames are visible to the unaided human eye, and in daylight, they can be “seen” by an ultraviolet light sensor.5 If a hydrogen flame ignites other nearby materials, flames or smoke may also be visible from them. See Figure 13. Figure 13. Hydrogen Flame Source: College of the Desert, 2001c. 2.1.2 Odor and Toxicity Hydrogen gas has no color, taste, or smell. Therefore, a gaseous hydrogen leak cannot generally be detected by human senses alone, except perhaps by human hearing.6 Other gaseous fuels, such as methane (natural gas), are also naturally colorless and odorless. However, sulfur-ba odorants sed 7 are usually added to pipeline natural gas specifically to aid in detecting leaks. The sulfur in these odorants can poison the catalysts used in automotive fuel cell systems, and satisfactory substitute odorants compatible with fuel cells have not yet been developed. Hydrogen sensors must be used to detect hydrogen leaks. There are a number of technologies used to sense hydrogen, but many sensors rely on a catalyst that contains palladium, which breaks the chemical bonds between the atoms in a hydrogen molecule. The hydrogen atoms then diffuse into the catalyst, changing its electrical properties (e.g., resistance, capacitance). This change is proportional to the hydrogen concentration and can, therefore, be used to measure hydrogen levels in the air (Speer, 2004). Hydrogen is not toxic to humans or animals. However, if leaking into an enclosed space, hydrogen gas can displace oxygen in the air and would pose an asphyxiation hazard in high enough concentrations. The risk of asphyxiation from hydrogen leaking into an open area is virtually non-existent because hydrogen is so buoyant that it will rise and diffuse to very low concentrations quickly. Even in an enclosed area the danger from a small leak is slight, but may 5 Very little of the energy given off by a hydrogen flame is in the infrared part of the light spectrum. Infrared sensors are better suited to hydrocarbon fires. 6 Escaping hydrogen gas may produce an audible noise, depending on the size and rate of the leak. 7 These include mercaptans and thiophanes. 23 be greater from a large leak that releases a significant volume of hydrogen relative to the size of the space. 2.1.3 Buoyancy and Diffusivity Hydrogen is the smallest and lightest known molecule, and therefore is the “lightest” gas. Hydrogen has only 7 percent of the density of air, which means that a given volume of air will weigh fourteen times as much as the same volume of hydrogen gas at atmospheric pressure. Because it is so light and the molecules are so small, hydrogen leaking from a vessel rises and diffuses very quickly in air. The rate of diffusion for hydrogen in air is over ten times the rate for gasoline and other fuel vapors (Raj, 1998). This means that leaked hydrogen will quickly dissipate in open air to the point that the mixture is no longer flammable. 2.1.4 Effect on Materials Hydrogen is the smallest of all molecules, and it can diffuse through materials that other gases cannot. Seals and connections in high-pressure hydrogen storage systems must, therefore, be designed very carefully, with attention to both the materials used and the geometry of the mating surfaces of joints. Over time, constant exposure to hydrogen can cause many materials to loose strength and develop small cracks. This phenomenon is called hydrogen embrittlement, and it can cause leakage or catastrophic failure in hydrogen tanks and lines. The mechanisms of hydrogen embrittlement are not well-understood, but certain factors are known to effect the rate of embrittlement, including hydrogen concentration, pressure, and temperature. Stainless steel is more resistant to hydrogen embrittlement than ordinary steels, and both pure aluminum and many aluminum alloys are even more resistant than stainless steel if the gas is dry (Ringland, 1994). All components of hydrogen fuel systems must be constructed of materials known to be compatible with hydrogen. During maintenance and overhaul, only manufacturer-approved replacement parts specifically designed for use in hydrogen systems must be used. Parts that “look the same,” even if they fit properly, could result in failures over time if they are made from incompatible materials. 24 2.1.5 High-Pressure Storage Hydrogen gas contains a lot of energy per pound, but like all gases it is difficult to compress. In order to get enough hydrogen fuel on a vehicle to operate for several hundred miles or more between fill ups, it must be stored at very high pressures—typically between 5,000 and 10,000 pounds per square inch (psi). Gaseous hydrogen fuel with the same amount of energy as one gallon of diesel fuel would only weigh about one third as much, but would occupy almost seven times the volume if stored at 10,000 psi.8 If stored at only 3,000 psi, the hydrogen would occupy almost seventeen times the volume of the diesel fuel. The use of high-pressure storage does introduce some potential hazards due to the large amount of mechanical energy in the compressed gas. However, the high-pressure storage tanks used to hold compressed hydrogen are designed with a high margin of safety, and designs are verified with extensive qualification testing. See Figure 14 for photos of the types of tests required for certification of a high-pressure storage tank design. High-pressure storage tanks are also protected from excessive pressure build-up inside the tank using pressure relief devices (PRD) and/or temperature relief devices (TRD). These devices act to vent hydrogen to relieve pressure in the tank if it gets so high that there will be danger of a rupture. Figure 14. High-Pressure Storage Vessel Qualification Tests Source: Photos courtesy of College of the Desert, 2001a. High-pressure storage tanks must be protected from abrasion or damage by road debris, and both the tanks and lines should be adequately protected from vibration to minimize the possibility of leaks. 8 Not including the weight and volume of the hydrogen tank itself. 25 2.1.6 Gaseous Hydrogen Leaks Because hydrogen molecules are so small, leaking hydrogen gas rises and diffuses quickly. A gaseous hydrogen leak tends to create a very vertical, fairly narrow area in which the hydrogenair mix is flammable. Outside of this region, the hydrogen concentration is too low for the mixture to burn. Depending on size and flow rate, the leak may produce a hissing sound similar to other gas leaks. Gaseous hydrogen leaks may self-ignite due to static electricity or heating created by the flow of hydrogen. If the leak does ignite, the flame will be virtually invisible in daylight. 2.2 LIQUID HYDROGEN Liquid hydrogen is gaseous hydrogen that has been cooled to the point that it condenses. To get hydrogen to condense to a liquid it must be cooled to −423ºF—just a few degrees warmer than “absolute zero,” which is as cold as anything can get. Liquid hydrogen is referred to as a “cryogenic liquid” because it is so cold, and must be stored in specially insulated containers. As liquid hydrogen absorbs heat, some of the liquid “boils off” and vaporizes. Once it has vaporized, the resultant hydrogen gas has the same properties and presents the same hazards as discussed above. However, while in liquid form, it presents additional hazards related to the extreme cold of the liquid. In addition, liquid hydrogen leaks behave somewhat differently than gaseous hydrogen leaks. Figure 15. Liquid Hydrogen Temperature 2.2.1 Low Temperature Storage Liquid hydrogen storage vessels must also be well-insulated to maintain the temperature of liquid hydrogen over long periods. No matter how well-insulated, however, it is inevitable that eventually some heat will be absorbed through the vessel walls, which will cause some hydrogen in the tank to vaporize. As hydrogen vaporizes, it raises the vapor pressure inside the tank. If not relieved, the increased pressure might eventually cause the tank to rupture. 26 The extremely low temperature of liquid hydrogen poses a severe frostbite hazard to exposed skin. All vessels, hoses, and lines that carry liquid hydrogen, either on a vehicle or at a fueling station, should be protected to avoid casual contact by people. Liquid hydrogen tanks are always equipped with pressure relief valves to relieve pressure in the tank as necessary. These valves are different from the PRD/TRDs used with gaseous hydrogen storage tanks. Liquid hydrogen pressure relief valves are designed to open when the vapor pressure inside the tank rises above a set pressure, and then to close again when the pressure inside the tank falls below a different set pressure. PRD/TRDs open as required to relieve pressure, but do not close again. Once a PRD/TRD opens, it must be replaced before the tank can be filled again. 2.2.2 Effect on Materials The extremely low temperature of liquid hydrogen makes many materials brittle and easily broken. This includes most metals, including many grades of carbon steel and low alloy steels, and many of the materials typically used for sealing joints in liquid storage systems, such as rubber and many plastics. Liquid hydrogen storage systems must be constructed from very specific materials that can maintain their strength at low temperatures. Liquid hydrogen storage tanks and lines are usually constructed from stainless steel, and nonwelded joints may be sealed with o-rings made from specialized materials specifically tested to be compatible with the extremely low temperature of liquid hydrogen. 2.2.3 Liquid Hydrogen Leaks Leaking liquid hydrogen may spread on the ground for a short distance, but the liquid will quickly evaporate, creating a cloud of gaseous hydrogen over the liquid pool. The distance of spread and the rate of evaporation will depend on the size of the leak and on ambient conditions. The hydrogen cloud over the liquid pool will be very cold and dense, but will rise and dissipate as it is warmed by surrounding air. Often the cold hydrogen will condense water vapor in the air, creating a visible fog in the area of the leak. Frost or ice may also form on the storage vessel or lines in the area of the leak. The cloud of cold gaseous hydrogen may move horizontally as it warms and rises, and may extend beyond the area of visible fog. This hydrogen cloud may be cold enough to cause frostbite to exposed skin and should be avoided. Leaking liquid hydrogen is so cold that it can liquefy the oxygen and nitrogen in surrounding air. If liquid oxygen drips onto combustible material (for example, asphalt), it will significantly increase the fire hazard. This is not of major concern for the volumes of liquid hydrogen likely to be carried on a typical commercial vehicle. However, liquid hydrogen storage tanks at fuel stations, which are likely to contain a much greater volume of fuel, should always be constructed over pads made of noncombustible material, such as concrete. For the same reason, the insulation on the exterior of all liquid hydrogen storage tanks and lines, both at the fuel station and on a vehicle, should be vapor sealed to ensure that air cannot contact the cold inner surface. 27 2.3 COMPARISON OF HYDROGEN TO OTHER MOTOR FUELS This section directly compares the properties of gaseous and liquid hydrogen to those of diesel fuel to contrast the safety issues of hydrogen to those of more common motor fuels. Two specific areas will be highlighted: the behavior of fuel leaks, and the characteristics of fire and explosions with these fuels. 2.3.1 Leaks In some ways a gaseous hydrogen fuel leak is less dangerous than a leak of diesel fuel or gasoline. Leaking diesel fuel and gasoline can puddle and spread over a large area, and the puddles will persist because they evaporate slowly (Amerada Hess, 2001). Gaseous hydrogen leaks tend to be vertical with only a relatively narrow area/volume in which a flammable mixture exists;9 the hydrogen quickly dissipates in open air to nonhazardous levels. If designed properly, the most likely location of a major hydrogen leak from a vehicle will be through the PRD, which should vent away from the occupied area of the vehicle. PRDs are designed to vent the entire contents of a hydrogen tank in only a few minutes, after which there is no lingering risk of hydrogen fire or explosion if the release was in the open air. Large hydrogen leaks inside buildings are more dangerous unless the facility has been designed to evacuate the leaked gas and to minimize ignition sources at ceiling level. Leaking liquid hydrogen can pool and spread, but will quickly evaporate as it is heated by the surrounding air. As it evaporates, the cloud of gaseous hydrogen formed over the spill may move horizontally as it rises and dissipates. While diesel fuel and gasoline leaks are easily visible and accompanied by a strong characteristic smell, gaseous hydrogen leaks are invisible and odorless (see Table 5). The only indication of a gaseous hydrogen leak may be a whistling noise similar to escape of other high-pressure gases. A liquid hydrogen leak may be accompanied by an area of fog surrounding the leaking hydrogen and/or the formation of frost on the tank or lines in the vicinity of the leak, because the super cold hydrogen cools the surrounding air and causes water vapor to condense.10 9 The actual area/volume in which a flammable mixture will exist will depend on the rate and size of the leak and on ambient conditions. 10 This fog and frost may not appear in locations with very low humidity. 28 Table 5. Leak Profiles of Gaseous Hydrogen, Liquid Hydrogen, and Diesel Fuel Leak Profile Gaseous Hydrogen Liquid Hydrogen Diesel Fuel Location Gas quickly rises May be liquid puddle – gas rises as it evaporates Liquid puddle on ground and some vapors low to ground Size Very vertical and localized Puddle will not spread far – gas may spread horizontally as it rises Puddle can spread on ground Duration Quickly dissipates in open, but may collect at ceiling in buildings Liquid evaporates quickly and gas dissipates in open, but gas may collect at ceiling in buildings Liquid evaporates slowly Visual Detection? No Maybe- potential fog and frost in area of leak Yes Odor? None None Yes Flammability Very easily ignited Very easily ignited Easily ignited Flames Invisible in daylight Invisible in daylight Visible and smoky 2.3.2 Fires and Explosion Hydrogen has higher energy content (per pound) than diesel fuel and is very reactive, which results in a very vigorous fire. However, the buoyancy of gaseous hydrogen means that it rises rapidly and diffuses quickly, resulting in a very vertical and localized flame. Hydrogen fires also tend to burn out fairly quickly. By contrast, diesel fuel and gasoline fires tend to burn longer and spread over a much larger area, as the liquid fuel puddle expands. There is virtually no risk of a thermal “explosion” of hydrogen stored in a closed tank unless oxygen has been allowed to enter the tank during fueling operations, which is virtually impossible if the fueling system has been designed properly. Hydrogen gas that leaks into an enclosed space, whether on a vehicle or in a building, can create an explosive mixture, depending on the volume of hydrogen relative to the volume of air in the space. 29 Diesel fuel is not very volatile, and the risk that accumulated vapors will result in an explosion is small, even for large leaks. Gasoline, however, is very volatile and vapors from leaks can create the risk of an explosion if they collect in an enclosed space on the vehicle or in a building. 2.4 HYDROGEN SAFETY PRINCIPLES The most important safety principle in any situation is education—making anyone who will come into contact with a vehicle aware of a potential hazard. For hydrogen and other alternativefueled vehicles, this is done with appropriate labeling, to let users, emergency responders and the public know that hydrogen is present. As with other motor fuels, fire and explosion are the most significant everyday hazards associated with hydrogen. Also as with other fuels, a hydrogen leak from a vehicle’s fuel or engine system, or from a fueling station, provides the starting point for all fire and explosion hazards. Safe design for using hydrogen therefore requires attention to these safety principles: • Properly label all vehicles that use hydrogen fuel. Avoid fire and explosion by: Avoiding leaks through proper design and maintenance, Providing leak detection systems to detect leaks and, if a leak is detected, shut off the fuel system as soon as possible, • Removing ignition sources from areas where leaked hydrogen might be present, and • Properly ventilating all enclosed spaces where leaked hydrogen might accumulate. These are essentially the same principles that apply to the use of any gaseous fuel (e.g., natural gas), but their application may be slightly different based on the properties of hydrogen. Each of these principles, as applied to hydrogen, is discussed further below. 2.4.1 Labeling As with other alternative-fueled vehicles, all commercial vehicles that store hydrogen fuel onboard should carry a label that identifies the type of fuel used in order to alert emergency response personnel to the types of hazards they might face if the vehicle is involved in an accident. These labels should conform with SAE J2578, a fuel cell safety recommended practice developed by the Society for Automotive Engineers (SAE, 2002). This practice recommends a diamond-shaped label with a blue background and white lettering (see Figure 16). It also specifically recommends that the words “Compressed Hydrogen” or “Liquid Hydrogen” be contained in the blue diamond, depending on the form in which the hydrogen is stored on the vehicle. SAE J2578 does not specify the location of the hydrogen label on the vehicle. For hydrogenfueled cars, the manufacturer usually affixes the label to the rear of the vehicle, as shown in Figure 16. For commercial tractor-trailer units, a label on the rear of the power unit would likely be obscured by the trailer. For that reason, all commercial vehicles should include the hydrogen label on the rear of the vehicle and on each side of the power unit cab, below the DOT numbers 30 mandated by 49 CFR 390.21. As with these DOT numbers, the hydrogen labels should be legible from fifty feet in daylight. Figure 16. Hydrogen Vehicle Label in Accordance with SAE J2578 Any commercial trailer unit that will store hydrogen (for example, to fuel a transportation refrigeration unit) should also have SAE J2578-compliant hydrogen labels affixed. These labels should be located on the rear of the trailer and on each side of the trailer, in the vicinity of where the hydrogen fuel tank is located. 2.4.2 Avoiding Fire and Explosion As shown in Figure 17, a fire or explosion requires three things: • Fuel (i.e., a hydrogen leak), • An ignition source, and • Oxygen (from the air). Safe design for use of any gaseous fuel, including hydrogen, involves paying attention to all three legs of the “fire triangle.” Figure 17. Fire Triangle 2.4.2.1 Removing the Fuel Source—Avoiding and Detecting Leaks Good design for a fuel system involves two major principles: 31 • Avoiding leaks of hydrogen fuel • Detecting leaks of hydrogen fuel The most likely locations for a hydrogen leak are at joints and connections in the high-pressure hydrogen fuel system. Hydrogen gas is the smallest of all molecules and can, therefore, move more easily through joints than other gases. However, most hydrogen leaks can be avoided by designing hydrogen systems using appropriate materials and minimizing connections. Proper maintenance practices, in accordance with the manufacturer’s instructions, are also critical. This includes the use of the proper tools when making and breaking connections, tightening to the correct torque as specified by the manufacturer, and use of only approved replacement parts. In a properly designed and maintained hydrogen fuel system, the most likely location for a hydrogen release will be through the PRD/TRD. If the PRD/TRD is properly oriented, a release will pose little danger to the vehicle, the operator, or the public. Hydrogen-fueled vehicles should enter only buildings designed to handle hydrogen. All vehicles that use hydrogen fuel should also be equipped with one or more sensors to detect hydrogen leaks. These sensors should be linked to the vehicle control system. If hydrogen levels approaching the lower limit of flammability are detected, the system will automatically shut down the vehicle and close valves to isolate the hydrogen within the high-pressure tank. In most cases, this will stop the source of the leak and remove any hazard. Some vehicles may include an “override” switch that will allow the vehicle to operate for a short time, even after a hydrogen leak has been detected. This switch should only be used in case of extreme emergency, for example, to move the vehicle out of high speed traffic or off of a railroad track. Buildings used to store or maintain hydrogen-fueled vehicles should also generally be equipped with hydrogen sensors. These sensors will be hooked into a building alarm system, as well as the building’s ventilation system. If hydrogen levels approaching the lower limit of flammability are detected, the system will sound an alarm to warn people in the area to evacuate and will increase the ventilation rate in the building to help remove any accumulated hydrogen. Some buildings designed for hydrogen vehicles may also be equipped with ultraviolet flame detectors to detect hydrogen fires. If so, they will also be hooked to the building alarm system. 2.4.2.2 Removing Ignition Sources Hydrogen is very easily ignited. A spark from static electricity, a vehicle tailpipe, electrical device, or even a hot surface can all ignite a mixture of air and leaked hydrogen within its flammable range. 32 33 It is important to minimize potential ignition sources in areas where hydrogen might leak and collect. On a vehicle, static electricity is removed by proper grounding and bonding of electrical components. Fuel tanks, lines, and connections should be deliberately placed so that they avoid surfaces that might be hot or a source of ignition. In a building that will be used to house or maintain hydrogen fueled vehicles, any leaked hydrogen will quickly rise. The only area in which it is likely to collect in flammable concentrations is within a few feet of the ceiling. Electrical lines and equipment and heating equipment should not be located in this area near the ceiling. If electrical equipment must be located near the ceiling, it should be sealed so that it is “explosion proof” or intrinsically safe. 2.4.2.3 Ventilating Enclosed Spaces Hydrogen leaking into open air poses very little danger to anyone—it will quickly dissipate to nonflammable levels. Hydrogen that leaks into an enclosed space potentially presents a much greater hazard. When designing a hydrogen fueled vehicle, it is important to minimize all potential for hydrogen to leak into the passenger compartment, trunk, cargo space, wheel wells, and other enclosed spaces. This is done through careful placement of fuel tanks, lines, and connections. It may also be advisable to provide ventilation openings in locations that might not otherwise require them, specifically to vent any leaked hydrogen. Another important consideration is placement of the outlet for any PRDs/TRDs. These outlets should be at the top surface of the vehicle and pointed away from the passenger or cargo compartment. Buildings that will be used to house or maintain hydrogen-fueled vehicles should be designed so that there are no dead pockets at the ceiling where leaked hydrogen might collect and not be swept in by the building’s ventilation system. 3. GUIDELINES FOR DESIGN AND OPERATION OF HYDROGEN SYSTEMS ON VEHICLES Safe use of hydrogen as an alternative fuel requires that vehicles be designed and operated with the physical and chemical properties of hydrogen in mind. These properties are discussed in chapter 2. In most aspects, commercial vehicles powered by hydrogen will be quite similar to those powered by diesel fuel, but the propulsion system will be significantly different and some hydrogen-specific design elements are required. Likewise, operation of these vehicles will be similar to operation of diesel-fueled vehicles, with a few specific exceptions. This chapter briefly discusses the most important hydrogen-specific aspects of vehicle design and operation. The issues discussed are of necessity generalized and are based on current codes and standards and best practices (see Appendix B). Each vehicle manufacturer will develop their own specific designs, which are likely to vary significantly in their details, while adhering to the same over-all design principles. The information in this chapter is intended to familiarize commercial vehicle operators with the types of safety systems they are likely to see on hydrogen-fueled vehicles and the general operating principles they will need to use with them. Vehicle operators should look to the manuals provided by the manufacturer with each hydrogen-fueled vehicle for specific operating and maintenance instructions. 3.1 GASEOUS HYDROGEN SYSTEMS The most common method of storing hydrogen fuel on a vehicle is storage as a high-pressure gas, at pressures of 5,000–10,000 psi. This section discusses onboard gaseous hydrogen storage systems. 3.1.1 Design The exterior of the vehicle should be marked with diamond-shaped labels that say “Compressed Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab below the DOT numbers. The hydrogen labels should be legible from fifty feet in day light. The hydrogen fuel system will likely include two pressure regulators, which reduce the gas pressure in stages from the fuel storage cylinders to a fuel cell or hydrogen ICE. The three stages are: • The fuel storage system at up to 5,000 psi, • The motive pressure circuit at up to approximately 175 psi, and • The low pressure circuit at approximately 15 psi. 34 Each stage will include pressure relief devices, isolation valves, and other valves to regulate the flow of gas under all conditions. All components should be designed to withstand at least three times their expected maximum working pressure (NFPA, 2005). Storage cylinders used to hold compressed hydrogen gas must be tested and certified by the manufacturer to withstand the normal forces expected during vehicle operation (such as working pressure, pressure shocks from fueling, and vibration) over a 15-year life, as well as certain extreme events such as would be encountered in a vehicle crash. These cylinders should be permanently marked “hydrogen,” securely mounted to the vehicle with the certification label visible, and protected from damage by road debris (i.e., if mounted between the frame rails, they should be protected by a cover). All hydrogen storage cylinders must have a PRD or TRD installed. The outlets from each PRD/TRD should be connected to a common manifold that exits at or above the top surface of the vehicle, with outlet flow directed away from vehicle occupants and pedestrians. Each hydrogen storage cylinder should have a manual shut-off valve installed that will allow that cylinder to be isolated from the rest of the fuel system for maintenance. The fuel system should include one or more electrically activated valves that will isolate the hydrogen storage cylinders, individually or as a group, from the rest of the system when closed. These valve(s) should “fail safely” so that they will close if the control signal is lost due to a system fault. All hydrogen fuel lines should be securely mounted to the vehicle and routed away from heat sources. To the extent possible, fuel line connections should be minimized since leaks are most likely at joints. Fuel lines should not be routed through the passenger compartment. All components of the fuel system, including cylinders, lines, valves, and sealing materials should be constructed of materials that have been tested to be compatible with hydrogen and not subject to hydrogen embrittlement. All components of the fuel system and engine system that will carry or contain hydrogen should be electrically grounded and bonded to the vehicle chassis to preclude the build up of static electricity. Any compartment into which hydrogen could leak (from a fuel line connection or valve or from the fuel cell stack) should be ventilated such that hydrogen cannot collect in concentrations greater than 25 percent of hydrogen’s lower flammable limit. Hydrogen carrying components should not be located such that hydrogen can leak into the passenger compartment under any circumstance. Because fuel cell stacks can develop internal leaks over time, they will likely be installed in their own enclosure, which will have both ventilation holes and a ventilation fan to force air through the enclosure to flush out any leaked hydrogen so that it can not collect. One or more hydrogen sensors should be installed on the vehicle. The number and location of these sensors will depend on the hydrogen fuel and engine system design. These hydrogen sensor(s) should be connected to the vehicle control system to provide an alarm and automatic system shutdown if a hydrogen concentration greater than a preset threshold is detected. This 35 threshold could be anywhere from 25 percent to 50 percent of the lower flammable limit for hydrogen (1–2 percent hydrogen concentration). The fuel system may also have an excess flow valve installed that is designed to close off fuel flow and trigger an automatic system shutdown when flow in excess of a set threshold is detected. The threshold is set to be greater than the maximum flow that could be used by the fuel cell or hydrogen ICE at full power. Flows greater than this amount indicate that there is probably a leak in the system. The vehicle may also have an inertial crash sensor installed, which can automatically trigger a vehicle shutdown when a crash is detected. The vehicle control system should be configured so that automatic system shutdown can be triggered by detection of leaked hydrogen, excess fuel flow, a vehicle crash, or other system fault. Automatic system shutdown should include closing valve(s) to isolate hydrogen in the hydrogen storage cylinders, disconnecting traction power, and de-energizing high-voltage equipment. During system shutdown, hydrogen should be vented from all other fuel and engine system components. Some vehicles may include a switch to override automatic shutdown and allow the vehicle to continue to operate for a short time. This switch should only be used in case of extreme emergency, for example, to move the vehicle out of high-speed traffic or off of a railroad track. The control system should also include a single main on/off switch that allows the vehicle operator to shut down the fuel cell system, disconnect traction power, de-energize high-voltage equipment, and shut off hydrogen fuel supply (isolating all hydrogen in the hydrogen storage cylinders). This switch should be located in the operator’s cab easily accessible to the operator, similar to a conventional ignition switch. Some vehicles may also have one or more secondary means of shutting down the system, for example, by opening a battery disconnect switch accessible from outside the vehicle. The vehicle control system should include an interlock to the vehicle fueling port such that fueling cannot begin unless the fuel cell system is shutdown and the vehicle traction system is de-energized so that the vehicle cannot move. The onboard fuel filling receptacle must be electrically bonded to the vehicle chassis, and some method must be provided to electrically connect the vehicle chassis to the fuel station ground during fueling. This can be done through the fueling nozzle (preferred) or with a separate ground strap. A dust cap permanently mounted to the vehicle should be provided for the onboard fuel filling receptacle, to keep out dirt and debris when the vehicle is not being fueled. The vehicle fuel system should include fittings and other provisions necessary to de-fuel safely from the hydrogen storage cylinders and purge the cylinders with nitrogen, as required for maintenance. After system shutdown, hydrogen will typically be vented from the low-pressure sections of vehicle’s fuel system and fuel cell stack. The outlet for this venting hydrogen should be at or 36 above the top surface of the vehicle. If, under normal operations, venting hydrogen will achieve concentrations greater than 25 percent of the lower flammable limit (1.0 percent hydrogen concentration), the hydrogen should vent through a hydrogen diffuser. The hydrogen diffuser should be designed to mix the exiting hydrogen gas with enough air that under normal operations the resultant flow will have a hydrogen concentration less than 25 percent of the lower flammable limit. 3.1.2 Operation and Maintenance Anyone who will operate or maintain hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen, operation of onboard safety systems, hydrogen fueling operations, and actions to take in an emergency. During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with hydrogen (for example, lines, valves, and regulators designed for use with natural gas). While they may look and function the same, they may be subject to hydrogen embrittlement. In addition, compressed natural gas fuel systems typically operate at lower pressures (maximum 3,600 psi) than hydrogen fuel systems. Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Leak checks should also be conducted after repair or replacement of any fuel system lines or valves. Never loosen any joint in the fuel system while the connected components are under pressure. Shut down the system and isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the service manual. Do not over tighten. Overtorquing can cause leaks. Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, some components, particularly hydrogen fuel cylinders, must be purged with nitrogen before being refilled with hydrogen. See the manufacturer’s service manual for specific purging procedures. Periodically check the exterior surface of hydrogen fuel cylinders for nicks, dents, and cuts that could weaken the structure. See the manufacturer’s service manual for information on the allowable level of wear and damage before cylinders need to be replaced. The Federal Motor Vehicle Safety Standards applicable to natural gas fuel cylinders (FMVSS 304, 49 CFR 571.304) specify that a visual inspection by a “qualified container inspector”11 must be conducted “at least every 36 months or 36,000 miles or at the time of re-installation.” The inspection procedures for damage assessment are outlined in pamphlet C-612 from the Compressed Gas Association. While standards specifically applicable to hydrogen cylinders have not yet been developed, at a minimum, the requirements applicable to natural gas fuel cylinders should be followed. Local laws and regulations may require more frequent cylinder inspections, for example, in conjunction with 11 “CSA America is the only known standards development organization in the United States that provides testing and certification for qualified compressed natural gas (CNG) cylinder inspections and maintains a National Registry of Certified Inspectors. To qualify for a new certification or to renew an existing certification, candidates must successfully pass a certification exam. To maintain their status without reexamination, certified CNG Inspectors must perform and submit reports on 10 vehicle or 50 cylinder inspections per year.” 12 Compressed Gas Association, Inc., Pamphlet C-6: Standards for Visual Inspection of Compressed Gas Cylinders, 1984. 37 annual registration safety inspections. The fuel system, including the high-pressure storage tanks, should also be visually inspected after any accident, and be retested or replaced as required. Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual. Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans in accordance with the schedule and procedures in the manufacturer’s service manual. The fuel system will likely include a coalescing filter to remove any oil that might carry over into the hydrogen fuel from the fuel station compressor. Check and empty or replace this filter periodically in accordance with the schedule and procedures in the manufacturer’s service manual. Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off of railroad tracks). Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or gaseous hydrogen storage system, also disconnect the vehicle’s 12/24-VDC battery and close the manual fuel valves to isolate hydrogen in the storage cylinders. Do not try to repair damaged fuel lines—replace them. Do not walk on hydrogen fuel cylinders or expose them to damage from impact or abrasion. Do not allow strong chemicals, such as battery acid or metal cleaning solvents, to contact the hydrogen fuel cylinders. Always electrically ground and bond the vehicle when fueling and defueling. Connect the ground strap or cable at the fuel station if one is provided. Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling. Do not smoke or use a cell phone when servicing or fueling the vehicle. If the vehicle must be defueled for servicing of the hydrogen fuel system, the rate of fuel release must be carefully controlled. Follow the instructions in the manufacturer’s service manual. Unless the hydrogen storage tanks will be removed, always leave a small amount of pressure in the tanks so that the internal pressure is a few psi above atmospheric pressure. Any time tank pressure falls below atmospheric, it is possible for air to enter, and the tank must be purged with nitrogen before refilling with hydrogen. 38 3.2 LIQUID HYDROGEN SYSTEMS Liquid hydrogen storage on vehicles is much less common than high-pressure compressed hydrogen storage. If your vehicle does store liquid hydrogen onboard, many of the design and operating considerations listed in Section 3.1 will apply, but since liquid hydrogen is stored at very low temperatures, the additional considerations listed below will also apply. 3.2.1 Design The exterior of the vehicle should be marked with diamond-shaped labels that say “Liquid Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab, below the DOT numbers. The hydrogen labels should be legible from fifty feet in day light. All cryotanks used to hold liquid hydrogen must be permanently marked “hydrogen,” securely mounted to the vehicle, and protected from damage by road debris. All liquid hydrogen cryotanks must have a safety pressure relief valve installed. The outlet(s) from the valve(s) should empty into a hydrogen diffuser, whose outlet is located at or above the top surface of the vehicle. The hydrogen diffuser should be designed to mix the exiting hydrogen gas with enough air that under normal operations, the resultant flow will have a hydrogen concentration less than 25 percent of the lower flammable limit. Each liquid hydrogen cryotank should have a manual shutoff valve installed that will allow that cylinder to be isolated from the rest of the fuel system for maintenance. Each liquid hydrogen cryotank should be equipped with a liquid level gauge that can be read from the vehicle cab and a pressure gauge that can be read locally on or near the tank. While certification standards for on-vehicle liquid hydrogen tanks have not yet been finalized, at a minimum, tanks should be tested/certified in the same way that current liquefied natural gas (LNG) tanks are tested. For each tank design, this includes a 10-foot and a 30-foot drop test of a full tank to ensure that the tank will not leak even if subjected to a severe crash, and a 20-minute flame test to ensure that the tank will not immediately vent even if impacted by a fire (SAE, 1997). The fuel system should include one or more electrically activated valves that will isolate the hydrogen cryotank(s), individually or as a group, from the rest of the system when closed. These valve(s) should “fail safely” so that they will close if the control signal is lost due to a system fault. All liquid and gaseous hydrogen fuel lines should be securely mounted to the vehicle and routed away from heat sources. To the extent possible, fuel line connections should be minimized since leaks are most likely at joints. Fuel lines should not be routed through the passenger compartment. All components of the fuel system that will come into contact with liquid hydrogen, including cryotank(s), fill lines, valves, and sealing materials should be constructed of materials that have 39 been tested to be compatible with the low temperatures of liquid hydrogen. All gaseous hydrogen fuel lines and valves (downstream of the cryotank heat exchanger) shall be constructed of materials that have been tested to be compatible with hydrogen and not subject to hydrogen embrittlement. All components of the fuel system and engine system that will carry or contain liquid or gaseous hydrogen should be electrically grounded and bonded to the vehicle chassis to preclude the buildup of static electricity. All components of the fuel system that will carry or contain liquid hydrogen must be wellinsulated, labeled, and be located to prevent casual contact by vehicle operators or maintenance personnel. The outer insulating layer must be vapor sealed to prevent air infiltration. Any fuel line that may be isolated between two closed valves with residual liquid hydrogen still inside (i.e., a fill line) must contain a pressure relief valve to vent hydrogen that vaporizes as the line heats up. These valve(s) should vent to a common plenum, with the pressure relief valve(s) on the liquid hydrogen cryotank(s). Any compartment into which hydrogen could leak (from a fuel line connection or valve or from the fuel cell stack) should be ventilated such that gaseous hydrogen cannot collect in concentrations greater than 25 percent of hydrogen’s lower flammable limit. Hydrogen carrying components should not be located such that hydrogen can leak into the passenger compartment under any circumstance. Because fuel cell stacks can develop internal leaks over time, they will likely be installed in their own enclosure, which will have both ventilation holes and a ventilation fan to force air through the enclosure to flush out any leaked hydrogen so that it can not collect. One or more hydrogen sensors should be installed on the vehicle. The number and location of these sensors will depend on the hydrogen fuel and engine system design. These hydrogen sensor(s) should be connected to the vehicle control system to provide an alarm and automatic system shutdown if a hydrogen concentration greater than a preset threshold is detected. This threshold could be anywhere from 25 percent to 50 percent of the lower flammable limit for hydrogen (1–2 percent hydrogen concentration). The fuel system may also have an excess flow valve installed that is designed to close off fuel flow and trigger an automatic system shutdown when flow in excess of a set threshold is detected. The threshold is set to be greater than the maximum flow that could be used by the fuel cell or hydrogen ICE at full power. Flows greater than this amount indicate that there is probably a leak in the system. The vehicle may also have an inertial crash sensor installed that can automatically trigger a vehicle shutdown when a crash is detected. Some vehicles may include a switch to override automatic shutdown and allow the vehicle to continue to operate for a short time. This switch should only be used in case of extreme emergency, for example, to move the vehicle out of highspeed traffic or off of a railroad track. The vehicle control system should be configured so that automatic system shutdown can be triggered by detection of leaked hydrogen, excess fuel flow, a vehicle crash, or other system fault. Automatic system shutdown should include closing valve(s) to isolate hydrogen in the hydrogen storage cylinders, disconnecting traction power, and de-energizing high voltage 40 equipment. During system shutdown, hydrogen should be vented from all other fuel and engine system components. The control system should include a single main on/off switch that allows the vehicle operator to shut down the fuel cell system, disconnect traction power, de-energize high voltage equipment, and shut off the hydrogen fuel supply (isolating all hydrogen in the liquid hydrogen cryotank(s)). This switch should be located in the passenger cab easily accessible to the operator, similar to a conventional ignition switch. The vehicle control system should include an interlock to the vehicle fueling port such that fueling cannot begin unless the fuel cell system is shutdown and the vehicle traction system is de-energized so that the vehicle cannot move. The onboard liquid hydrogen filling receptacle must be electrically bonded to the vehicle chassis, and some method must be provided to electrically connect the vehicle chassis to the fuel station ground during fueling. This can be done through the fueling nozzle (preferred) or with a separate ground strap. A dust cap permanently mounted to the vehicle should be provided for the onboard fuel filling port, to keep out dirt and debris when the vehicle is not being fueled. The vehicle fuel system should include fittings and other provisions necessary to safely remove hydrogen fuel from the liquid hydrogen cryotank(s) and purge them with nitrogen or helium as required for maintenance. After system shutdown, hydrogen will typically be vented from the vehicle’s low-pressure gaseous fuel system and fuel cell stack. The outlet for this venting hydrogen should be at or above the top surface of the vehicle. If, under normal operations, venting hydrogen will achieve concentrations greater than 25 percent of the lower flammable limit (1 percent hydrogen concentration), the hydrogen should vent through a hydrogen diffuser. The same hydrogen diffuser can be used for both this function and to diffuse hydrogen released through the fuel system pressure relief valve(s). 3.2.2 Operation and Maintenance Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency. During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks. 41 When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots. Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks. Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures. Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Leak checks should also be conducted after repair or replacement of any fuel system lines or valves. Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired. Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual. Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual. Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks). Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24- VDC battery. Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion. Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided. 42 Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling. Do not smoke or use a cell phone when servicing or fueling the vehicle. The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled. 3.3 HIGH VOLTAGE SYSTEMS Any voltage greater than 30 VAC or 60 VDC can harm humans through electric shock and is considered “hazardous voltage” (SAE, 2002). Hydrogen fuel cells produce electricity at nominal voltages of 300 to 600 VDC, which is used to power an electric drive system that operates at similar voltages (often after conversion to alternating current). The drive system may be designed with a hybrid-electric configuration. If so, there will also be a high-voltage battery pack installed on the vehicle. Hydrogen fueled ICEs do not produce electricity directly, but hydrogen ICE vehicles may also be designed with a hybrid-electric drive configuration. If so, they will also include a high-voltage battery pack and other high-voltage electrical components. 3.3.1 Design All electrical cables that carry greater than 30 VAC or 60 VDC should be considered highvoltage cables and should be permanently identified with orange covering material, and be located to preclude casual contact by vehicle operators and maintenance personnel. No high voltage cables should be routed through the passenger compartment. Figure 18. Hazardous Voltage Symbol Any part or connector energized with high voltage during normal operations should be located behind a cover or in an enclosure labeled with the hazardous voltage symbol. See Figure 18. Removal of the cover should require removal of special fasteners and/or should trigger an 13 Ullage space is the free vapor space available above the liquid level in a filled tank. 43 interlock system that de-energizes the high-voltage components. If the cover or enclosure is made of conductive material, it should be grounded to the vehicle chassis. The electrical system should include an automatic disconnect function that isolates both poles of any high-voltage source (fuel cell stack and/or high voltage battery pack) from other system components. The connectors used should be “fail safe” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered by the following: • Turning off the main switch • By automatic system shutdown (due to a hydrogen sensor detecting a leak, or other system fault that shuts off the hydrogen fuel supply) All high-voltage components should be designed with adequate electrical isolation to prevent “current leakage” between them and other electrical components or the chassis. The vehicle control system should include a ground fault monitoring system that can detect leakage current and set a warning light and/or take other action (up to automatic system shutdown) when a current above a set threshold is detected. 3.3.2 Operation and Maintenance When working on high-voltage systems, always ensure that the main switch is in the “off” position and tag it and/or lock it in that position so that no one else can turn the vehicle on. Always assume that high-voltage electrical components are live, even when the vehicle main switch is in the off position. Use a volt meter to check before touching any electrical component. Always use appropriate personal protective equipment, such as high-voltage gloves, when working on high-voltage systems. Follow the safety recommendations in the manufacturer’s service manual. Never wear jewelry when working around high-voltage systems. Always reinstall high-voltage covers and barriers. Reapply high-voltage labels if they are removed or damaged. Do not ignore warnings from the ground fault monitoring system. Follow instructions in the service manual to isolate and repair the source of the fault. Unrepaired ground faults can cause shocks or electrocution to vehicle occupants or service technicians. High-voltage electrical cables are designed with special shielding and insulation, and the exterior cover should be made from orange colored material. Always replace high-voltage wiring and harnesses with parts as specified by the manufacturer. Do not manufacture your own highvoltage harnesses or substitute non-approved parts. Remember that high voltage will always be present inside a traction battery or ultracapacitor pack (if vehicle has a hybrid-electric drive system) even when the main switch is off or automatic shutdown has occurred. Special tools and procedures are required to work safely 44 inside the battery/ultracapacitor pack. Do not open the battery/ultracapacitor pack cover unless you have been trained to work safely with live high voltage. 3.4 LIQUID FUEL REFORMERS A fuel reformer produces a hydrogen-rich gas onboard the vehicle from a liquid fuel, such as diesel fuel, gasoline, or methanol. This gas, called reformate, is 45–75 percent hydrogen and is used to feed a hydrogen fuel cell. See Section 1.4, Reforming of Liquid Fuels. The use of a fuel reformer eliminates the need to carry gaseous or liquid hydrogen on the vehicle since the fuel for the fuel cell is created on demand in the reformer. When the system is shut down, any residual reformate in the reformer and fuel cell stacks is usually vented, and there is virtually no hydrogen gas present on the vehicle. 3.4.1 Design The exterior of the vehicle should be marked with diamond-shaped labels that say “Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab, below the DOT numbers. The hydrogen labels should be legible from fifty feet in daylight. The working fluids inside a fuel reformer can be anywhere from 200–1500 °F while it is operating. All of the hot components should be packaged together and shielded to preclude casual contact by vehicle operators or maintenance personnel. These components should also be packaged on the vehicle to minimize the possibility that reformate leaking from the fuel cell stack will be able to contact any hot surfaces and ignite. The control system should include a single main switch that allows the vehicle operator to shut down the fuel cell system, disconnect traction or APU power, de-energize all high voltage equipment, and remove power from the reformer’s liquid fuel pump. This switch should be located in the passenger cab easily accessible to the operator, similar to a conventional ignition switch or APU on/off switch. A fuel cell vehicle with an onboard liquid fuel reformer has significantly less free hydrogen onboard than a fuel cell vehicle that carries compressed hydrogen gas or liquid hydrogen onboard. The reformate produced by fuel processors used with PEM fuel cells will contain hydrogen, carbon dioxide, nitrogen, and water. For SOFC APUs, the reformate produced by the fuel processor may also contain up to 30 percent carbon monoxide. Therefore, it is advisable to include one or more hydrogen sensors when a PEM fuel cell is used, or combustible gas sensors that can detect both hydrogen and carbon monoxide when an SOFC is being used, on the vehicle to detect leaks of reformate from the fuel cell stack while it is operating. These sensor(s) should be connected to the vehicle control system to provide an alarm and automatic system shutdown if a hydrogen or carbon monoxide concentration greater than a preset threshold is detected. Automatic system shutdown should include de-energizing the liquid fuel pump to shut off the flow of liquid fuel to the fuel reformer. During system shutdown, reformate should be vented from the reformer and fuel cell stack. 45 3.4.2 Operation and Maintenance Anyone who will operate or maintain vehicles with liquid fuel reformers should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen, operation of onboard safety systems, and actions to take in an emergency. Always assume that any fluid leaking from a fuel reformer is hot enough to cause injury. In general, most fuel reformer/processors will be designed to be “line replaceable units” and the vehicle operator or mechanic will have no reason to open up the “hot box.” Defective units will be removed from the vehicle and sent to the manufacturer for trouble-shooting and repair of internal components. If you have reason to open up a fuel processor enclosure, allow time after system shutdown for the internal components and the working fluids to cool down. In some cases, these components may stay hot for hours or days. See the manufacturer’s service manual for working temperatures and cool down periods. Periodically check any external connections from the fuel reformer to other vehicle systems (i.e., fuel line) for signs of leaks using the procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Periodically check electrical connections from the fuel processor/SOFC APU to other vehicle systems for signs of corrosion or electrical arcing. The fuel processor may have air and/or fuel filters, as well as fuel desulfurization traps, that must be replaced periodically. See the manufacturer’s service manual for replacement intervals and procedures. 3.5 HYDROGEN INJECTION SYSTEMS Hydrogen injection systems create small amounts of hydrogen and oxygen through electrolysis, to supplement the diesel fuel in a standard diesel engine. See Sections 1.2.3 and 1.5. A hydrogen injection system for a diesel engine produces and uses significantly less hydrogen than a hydrogen fuel cell or hydrogen ICE, and does not require that compressed or liquid hydrogen be carried on the vehicle. The system is designed to produce hydrogen only when required, in response to driver throttle commands. When the system is shut off, no hydrogen should be present on the vehicle. 3.5.1 Design The exterior of the vehicle should be marked with diamond-shaped labels that say “Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab, below the DOT numbers. The hydrogen labels should be legible from fifty feet in daylight. The electrolyzer used to create hydrogen and oxygen should include an automatic disconnect function that isolates both poles of its power source (engine alternator or 12/24-VDC battery). 46 47 The connectors used should “fail safely” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered both by turning off the vehicle’s ignition switch and by any electrolyzer system fault. All hydrogen and oxygen lines from the electrolyzer to the engine air intake should be securely mounted to the vehicle and routed away from heat sources. These lines should not be routed through the passenger compartment or in any area that would allow hydrogen or oxygen to leak into the passenger compartment under any circumstance. The hydrogen lines from the electrolyzer to the engine’s air intake should be constructed of materials that have been tested to be compatible with hydrogen and not subject to hydrogen embrittlement. The electrolyzer and the hydrogen and oxygen lines from the electrolyzer to the engine’s air intake should be electrically grounded and bonded to the vehicle chassis to preclude the buildup of static electricity. Any compartment into which hydrogen could leak from the hydrogen lines should be ventilated such that hydrogen cannot collect in concentrations greater than 25 percent of hydrogen’s lower flammable limit. 3.5.2 Operation and Maintenance Anyone who will operate or maintain vehicles with hydrogen injection systems should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen, operation of onboard safety systems, and actions to take in an emergency. During maintenance, never substitute for the hydrogen lines replacement parts that have not been specifically tested and certified for use with hydrogen (for example lines, valves, and regulators designed for use with natural gas). While they may look and function the same, they may be subject to hydrogen embrittlement. Periodically check all connections from the electrolyzer to the engine’s air intake for leaks, using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Never loosen any joint in the hydrogen injection system while the system is operating. Before servicing, turn off the ignition and wait for the hydrogen injection system to vent, as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks. 4. GUIDELINES FOR DESIGN AND OPERATION OF HYDROGEN FUELING FACILITIES Safe fueling of hydrogen vehicles requires that hydrogen fueling facilities be designed and operated with the physical and chemical properties of hydrogen in mind. These properties are discussed in chapter 2. In addition to the general safety principles that apply to all fuel stations, there are some hydrogen-specific design elements and safety procedures that are required at hydrogen fuel stations. This chapter briefly discusses the most important aspects of hydrogen fuel station design and operation, with an emphasis on safety. The issues discussed are of necessity generalized, and are based on current codes and standards and best practices. Each fuel station manufacturer and operator will develop its own specific designs and operating procedures, which are likely to vary significantly in their details, while adhering to the same over-all safety principles. The information in this chapter is intended to familiarize commercial vehicle operators with the general safety aspects of hydrogen fueling. Vehicle operators should always follow specific instructions issued by each hydrogen fueling station they use. 4.1 COMPRESSED HYDROGEN FUELING A compressed hydrogen fuel dispenser is very similar to a compressed natural gas fuel dispenser, and the entire fuel station is often also very similar. Both will include a high-pressure compressor station to raise the pressure of the gas (hydrogen or natural gas) to fuel the vehicles. The major difference between a natural gas and hydrogen station is the source of the gas that will be compressed. Natural gas fuel stations are supplied with gas from a utility pipeline. Some hydrogen pipelines do exist in this country, but they are not widely available in most cities. Sometimes hydrogen is trucked to a fueling site from a hydrogen production facility in a tube trailer that stores the hydrogen at high pressure, and vehicles are fueled directly from these tubes (see Figure 19). Figure 19. Hydrogen Tube Trailer Photo courtesy of Sunline Transit. 48 Hydrogen can also be trucked to the fuel station and stored on-site as liquid hydrogen. If so, the fuel station will have a large liquid hydrogen cryotank and a vaporizer. A vaporizer is a large heat exchanger that is used to boil off the liquid hydrogen and raise the temperature of the resulting hydrogen gas. After it is vaporized, the hydrogen gas is then compressed into highpressure tanks for delivery to vehicles (see Figure 20). Figure 20. Liquid Hydrogen Storage Tank and Vaporizer Photo courtesy of Santa Clara Valley Transportation Authority. Hydrogen can also be produced on-site at the fueling station by electrolyzing water, by reforming natural gas, or both (see Sections 1.4 and 1.5). If the hydrogen is produced by reforming natural gas, the natural gas will be supplied by a utility pipeline. The reformer used will be similar to onboard fuel reformers as described in Section 1.4, but will be much larger and will include an additional processing step to separate the hydrogen from the other components of the reformate (carbon dioxide and nitrogen). See Figure 21. 49 Figure 21. Natural Gas Reformer Photo courtesy of Sunline Transit. Hydrogen dispensers look very much like gasoline or diesel dispensers, but the fueling nozzle is different (see Figure 22). The high-pressure fueling nozzle used with hydrogen is similar to those used with natural gas. A female coupling on the fueling nozzle mates with a male coupling on the vehicle, and the attendant turns a lever to lock the two together. Fueling can then begin (see Figure 23). The nozzle is likely to also include an electrical connection to establish communication between the fuel station controller and the vehicle system controller, as well as a bonding path to bond the vehicle to the fuel station so that static electricity cannot build up and cause a spark while fueling. Figure 22. Compressed Hydrogen Dispenser Photo courtesy of Santa Clara Valley Transportation Authority. 50 Figure 23. Compressed Hydrogen Fuel Nozzle Photo courtesy of Santa Clara Valley Transportation Authority. 4.1.1 Design It is generally recommended that all components of a hydrogen fuel station be located outdoors in open air. The facility should not be located under overhead wires, roadways, or overhanging buildings. If the fueling dispenser is located within a building, it must be a separate building with no uses other than for vehicle fueling and must be equipped with adequate ventilation and safety systems. See chapter 5 for design requirements for buildings that will house hydrogen fueling operations. If the fueling dispenser is covered by a rain canopy, it must be designed so that any hydrogen that leaks from the dispenser or vehicle being fueled cannot collect under the canopy. See Figure 24, which shows upwardly sloping canopies with smooth undersides over hydrogen fuel dispensers so that hydrogen cannot collect. Figure 24. Hydrogen Fueling Station Photo courtesy of Alameda Contra-Costa Transit District. 51 All components of the fuel station should be protected from damage by vehicles. Public access to all components except the fuel dispensers should be restricted. The minimum distance from any hydrogen equipment to other buildings or public roadways should be ten feet (NFPA, 2005). The hydrogen fuel dispenser should be designed with a “breakaway” device that shuts off fuel flow in case a vehicle moves away with the hose connected. A one-quarter turn manual isolation valve should be installed just upstream of the breakaway connection. All electrical equipment at the fuel station that might be exposed to hydrogen must be designed so that it cannot produce a spark. This is often done by sealing all openings in the equipment. All electrical equipment and any equipment that will hold or carry hydrogen, including the dispenser and fueling hose, must be electrically grounded and bonded to the facility. The vehicle being fueled must also be bonded to the facility. This can be done through the fueling nozzle connection or with a separate ground strap. If heat is provided at the fuel station, it must be provided using forced hot air, steam, or hot water. Open flame heaters should never be used. Fueling will likely be automated. Once the nozzle is locked securely in place, fueling will start and will automatically stop when the maximum rated fuel pressure is reached on the vehicle (i.e., 5,000 psig). Fuel should not flow unless a positive connection is made between the fuel nozzle and the receptacle on the vehicle. Fuel systems automatically adjust for temperature to ensure a full fill. Fueling in hot weather may result in a final pressure above the rated pressure; fueling in cold weather may result in a lower final pressure. The system should also be designed so that filling will not start when the pressure in the vehicle fuel tanks is less than atmosphere pressure (15 psia). Pressures lower than atmospheric indicate that air might have entered the tank, which could cause a significant fire and explosion hazard. The system should also be designed to automatically shut down if any fuel station fault is detected. Automatic shutdown should interrupt all electrical power to the fuel station equipment, including the compressors. The fuel station may include provisions for defueling a vehicle through the fueling nozzle or through a separate hose connection to the vehicle fueling port. Hydrogen leaving a vehicle during defueling may be routed to the suction side of the hydrogen compressor or may be vented to open air. If hydrogen is vented, the vent outlet should be higher than any surrounding buildings or structures and should include a hydrogen diffuser or flame arrestor. Any high-pressure hydrogen storage tank at the fuel station must be equipped with a PRD/TRD. The outlets from each PRD/TRD should be connected to a common vent stack. The top of the vent stack should be higher than surrounding buildings. If the hydrogen fuel station stores liquid hydrogen on-site, the liquid hydrogen cryotank must be equipped with a pressure relief valve. Any liquid hydrogen line that could be isolated between two closed valves with liquid hydrogen inside must also be equipped with a pressure relief valve. The outlets from these pressure relief valves should be connected to a common vent stack. The 52 top of the vent stack should be higher than any surrounding buildings and should be equipped with a hydrogen diffuser or flame arrestor. The fueling facility should include well-marked emergency stop buttons at each fuel dispenser and at each exit from the fueling area. Pushing an emergency stop button should interrupt all non-essential electrical power to the fuel station equipment. The station should include one or more hydrogen sensors and one or more ultraviolet flame sensors located to sense hydrogen leaks or flames in the vicinity of the fuel dispenser(s). These should be linked to the fuel station’s automatic shutdown system so that all electrical power to station equipment will be interrupted if a flame is detected or if hydrogen levels greater than 25 percent of the lower flammable limit are detected. Dry powder fire extinguishers should be located at the fuel station. Signs in place at the fuel station should include, at a minimum: • No smoking. • No cell phones. • Before fueling, vehicle ignition must be off, and vehicle must be grounded and bonded. • Hydrogen gas is odorless. • Location of emergency stop buttons. • Location of manual shut-off valves. • Location of fire extinguishers. 4.1.2 Operation and Maintenance Anyone who will operate a compressed hydrogen fueling station should receive training on fueling operations and hydrogen safety. At a minimum, this training should cover the characteristics of hydrogen, fueling procedures, operation of fuel station safety systems, and actions to take in an emergency. Smoking and the use of cell phones should never be allowed at the hydrogen fueling station. Other activities that could cause a spark or flame, such as welding and cutting or using jumper cables, should never be allowed at the hydrogen fueling station. Vehicle maintenance should not be done at the hydrogen fuel station. Before fueling a vehicle, turn off the ignition, set the parking brake, and electrically ground/bond the vehicle to the fuel station. Grounding/bonding may be done automatically through the fuel nozzle connection, but do not assume that it will. Check for a separate ground bond strap at the fuel dispenser and, if provided, follow instructions for its use. Do not fuel a vehicle with a known hydrogen fuel leak. When working on or around the hydrogen fuel station, use only nonsparking tools. 53 The hydrogen sensors, flame sensors, and other emergency equipment at the fuel station should be maintained, calibrated, and checked at least annually in accordance with the manufacturer’s instructions (NFPA, 2005). 4.2 LIQUID HYDROGEN FUELING If liquid hydrogen is carried on your vehicle, it must be fueled at a liquid hydrogen fuel station. The station will include one or more large liquid hydrogen cryotanks, and one or more dispensers with a liquid hydrogen fueling nozzle. Compressors and pumps are not used with liquid hydrogen. To get liquid hydrogen to flow from the cryotank, heat is added to the tank via a small heater. As the heat is absorbed, some liquid hydrogen vaporizes, raising the pressure in the tank, which pushes out liquid hydrogen. See Figure 25 for a photo of a liquid hydrogen storage tank and dispenser. The fuel nozzles used with liquid hydrogen look something like compressed hydrogen nozzles, but are more complicated (see Figure 26). A male coupling on the fueling nozzle mates with a female coupling on the vehicle, and the attendant turns a lever to lock the two together. Fueling can then begin. Figure 25. Liquid Hydrogen Storage Station 54 Figure 26. Liquid Hydrogen Fueling Nozzle and Vehicle Fuel Port Photo courtesy of Air Products and Chemicals. 4.2.1 Design All components of a liquid hydrogen fuel station should be located outdoors in open air. The facility should not be located under overhead wires, roadways, or overhanging buildings. Applicable codes prohibit liquid hydrogen cryotanks larger than 600 gallons and any liquid hydrogen fueling dispenser from being located inside a building (NFPA, 2005). These codes also specify minimum set-back distances between liquid hydrogen storage tanks and any occupied buildings or public roadways. These distances range from ten to seventy five feet, depending on the size of the liquid hydrogen storage tank(s). Any liquid hydrogen transfer point (i.e., liquid hydrogen dispenser) must be located at least twenty-five feet from the nearest building. If the fueling dispenser is covered by a rain canopy, it must be designed so that any liquid hydrogen that leaks from the dispenser or vehicle being fueled cannot collect under the canopy as it vaporizes and rises. See Figure 24, which shows upwardly sloping canopies with smooth undersides over hydrogen fuel dispensers so that hydrogen gas cannot collect. All components of the fuel station should be protected from damage by vehicles. The liquid hydrogen cryotanks and all facility piping other than the fueling hose should be located behind a barrier that will deflect any leaking liquid hydrogen away from personnel fueling vehicles. Public access to all components except the fuel dispensers should be restricted. All site drains and entrances to cellars and other underground facilities must be located far enough from the liquid hydrogen fuel station so that any leaked or spilled liquid hydrogen will vaporize before reaching the drain or opening. Depressions or dikes should be considered around the liquid hydrogen cryotank(s), as well as the dispensers to limit the spread of any spill. Liquid hydrogen that enters an underground space will create a significant fire and explosion hazard as it vaporizes. 55 All components of the fuel station that will carry liquid hydrogen should be well-insulated with the exterior surface of the insulation vapor sealed. They should be protected from casual contact with station personnel and vehicle operators. The liquid hydrogen storage tanks, lines, and dispensers should be mounted on a concrete pad. They should not be located over asphalt or any other combustible material. Leaking liquid hydrogen can condense (liquefy) surrounding air. Liquefied air is oxygen enhanced and will create a severe fire hazard if it drips onto combustible material. The hydrogen fuel dispenser should be designed with a “breakaway” device that will shut off liquid hydrogen flow in case a vehicle drives away with the hose connected. A manual, onequarter turn isolation valve should be installed just upstream of the breakaway connection. All electrical equipment at the fuel station that might be exposed to hydrogen must be designed so that it cannot produce a spark. This is often done by sealing all openings in the equipment. All electrical equipment and any equipment that will hold or carry liquid hydrogen, including the dispenser and fueling hose, must be electrically grounded and bonded to the facility. The vehicle being fueled must also be grounded and bonded to the facility. This can be done through the fueling nozzle connection or with a separate ground strap. If heat is provided at the fuel station, it must be provided using forced hot air, steam, or hot water. Open flame heaters should never be used. The liquid hydrogen cryotank(s) must be equipped with manual shut-off valves and electrically or pneumatically activated automatic shut-off valves. These valve(s) should “fail safely” so that they will close if the control signal is lost due to a system fault. The system should be designed to automatically shut down if any fuel station fault is detected. Automatic shutdown should interrupt all electrical power to the fuel station equipment and close the automatic shut-off valves at the liquid hydrogen storage tanks. The fueling facility should include well-marked emergency stop buttons within ten feet of each fuel dispenser and at each exit from the fueling area. Pushing an emergency stop button should interrupt all non-essential electrical power to the fuel station equipment and close the automatic shut-off valves at the liquid hydrogen storage tanks. The station should include one or more hydrogen sensors and one or more ultraviolet flame sensors located to sense hydrogen leaks or flames in the vicinity of the fuel dispenser(s). These should be linked to the fuel station’s automatic shutdown system so that all non-essential electrical power to station equipment will be interrupted, and the automatic shut-off valves at the liquid hydrogen storage tanks will be closed if a flame is detected or if hydrogen levels greater than 25 percent of the lower flammable limit are detected. The liquid hydrogen cryotank(s) must be equipped with pressure relief valves. Any liquid hydrogen line that could be isolated between two closed valves with liquid hydrogen inside must also be equipped with a pressure relief valve. The outlets from these pressure relief valves should 56 be connected to a common vent stack. The top of the vent stack should be higher than any surrounding buildings and should be equipped with a hydrogen diffuser or flame arrestor. A high-pressure air, nitrogen, or helium supply should be located at the liquid hydrogen fuel dispenser to clean ice and frost from the fueling nozzle as required. The fueling nozzles should be designed so that fuel can not flow until there is a positive lock between the nozzle and the fuel port on the vehicle. They should also have a self-closing end or an automatic shutdown device that will close off the flow of liquid hydrogen if the nozzle is disconnected from the vehicle. Dry-powder fire extinguishers should be located at the fuel station. Signs in place at the fuel station should include, at a minimum: • NO Smoking. • No cell phones. • Before fueling, vehicle ignition must be off and vehicle must be grounded. • Hydrogen gas does not have a distinct odor. • Location of emergency stop buttons. • Location of manual shut-off valves. • Location of fire extinguishers. 4.2.2 Operation and Maintenance Anyone who will operate a liquid hydrogen fueling station should receive training on fueling operations and hydrogen safety. At a minimum, this training should cover the characteristics of gaseous and liquid hydrogen, fueling procedures, operation of fuel station safety systems, and actions to take in an emergency. Smoking and the use of cell phones should never be allowed at the liquid hydrogen fueling station. Other activities that could cause a spark or flame, such as welding and cutting or using jumper cables, should never be allowed at the hydrogen fueling station. Vehicle maintenance should not be done at the hydrogen fuel station. Before fueling a vehicle, turn off the ignition, set the parking brake, and electrically ground and bond the vehicle to the fuel station. Grounding and bonding may be done automatically through the fuel nozzle connection, but do not assume that it will. Check for a separate ground and bond strap at the fuel dispenser and, if provided, follow instructions for its use. Because of the extremely low temperature of liquid hydrogen, spills can cause serious frostbite to exposed skin. Fueling attendants who connect and disconnect the liquid hydrogen nozzle from the vehicle should wear safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots. 57 58 In the past, some fueling couplings used with liquid hydrogen required heating and rinsing to separate the two parts and to disconnect them from the vehicle after fueling. Newer designs have improved the safety and speed of fueling operations through the use of a special coaxial “cold withdrawal coupling.” This allows the operator to disconnect immediately from the vehicle after refueling has stopped and to refuel rapidly multiple vehicles without waiting for the coupling to warm up in between. Nonetheless, ice and frost may occasionally form on the nozzle. Before connecting to the vehicle, the attendant should check the mating surfaces on both the dispenser nozzle and the vehicle fuel receptacle to ensure they are free of solid particles. If necessary, the attendant can use the high-pressure air, nitrogen, or helium at the dispenser to remove ice and frost from the nozzle before connecting. Do not fuel a vehicle with a known hydrogen fuel leak. When working on or around the liquid hydrogen fuel station, use only nonsparking tools. The hydrogen sensors, flame sensors, and other emergency equipment at the fuel station, should be maintained, calibrated, and checked at least every six months, in accordance with the manufacturer’s instructions (NFPA, 2005). 5. GUIDELINES FOR DESIGN AND OPERATION OF VEHICLE MAINTENANCE FACILITIES Indoor facilities that will be used to store or maintain hydrogen-fueled vehicles must be designed and operated with the physical and chemical properties of hydrogen in mind. These properties are discussed in chapter 2. Building design principles generally used to accommodate hydrogen are similar to those used to accommodate other gaseous fuels such as natural gas, but they differ significantly from design principles generally used when only diesel fuel must be accommodated inside the facility. This chapter briefly discusses the most important aspects of building design and operation to accommodate hydrogen use. The information in this chapter is intended to familiarize commercial vehicle operators with the general safety aspects of using hydrogen vehicles inside buildings. Building designers and owners must always follow the specific requirements of current local building codes and directives of public safety officials. The issues discussed here are, out of necessity, generalized and are based on current codes and standards and best practices. Given that there are so few hydrogen vehicles on the road, these codes and practices are not well-developed at this time. In the past, facilities designed for experimental hydrogen vehicles have been designed with elaborate safety systems that were costly to implement. A recent facility design study commissioned by the California Fuel Cell Partnership recommended that no changes were required to current standard design practices to accommodate hydrogen vehicles when building public parking structures, private garages, or vehicle maintenance shops (Parsons Brinckerhoff, 2004). The analysis showed that the leak scenarios investigated would not result in a flammable mixture of hydrogen inside any of these facility types. The recommendations of this study have not been universally adopted, and local officials may impose more stringent requirements that do require modifications to these types of facilities to accommodate hydrogen vehicles. In addition, this study looked only at small vehicles (5-passenger sedans) carrying relatively small amounts of hydrogen onboard (13 lbs.), limited the analysis to a single vehicle at a time inside any facility, and specifically excluded consideration of what would happen if a PRD/TRD released while the vehicle was inside. Commercial fleet vehicles are likely to carry significantly more hydrogen onboard and to have more vehicles concentrated at a single facility. It is also probably not prudent to rule out completely the possibility of a PRD/TRD release inside a maintenance facility for commercial vehicles. Based on experience with natural gas vehicles, the most likely time for a PRD/TRD release is during or shortly after fueling, due to an increase in internal tank temperatures during fueling. However, a PRD/TRD release during maintenance could never be ruled out unless the vehicle’s hydrogen tanks were emptied14 before bringing the vehicle inside the maintenance bay. 14 See Section 3.1.2 for a discussion of hydrogen tank defueling, including requirements for subsequent purging with nitrogen before refilling. 59 The discussion below takes into account the larger quantities of hydrogen that will typically be carried on hydrogen-fueled commercial vehicles compared to passenger vehicles and specifically addresses the possibility of a PRD/TRD release inside a facility. The discussion applies to indoor hydrogen fueling facilities and buildings that will be used for overnight or long-term storage or for maintenance of vehicles that carry compressed or liquid hydrogen onboard. Fuel cell vehicles that use an onboard liquid fuel reformer or diesel vehicles with a hydrogen injection system can be stored and maintained in any facility since they do not have any hydrogen onboard when the reformer or injection system is not operating. The below design guidelines are based on the following major principles: • Detect hydrogen leaks as soon as possible by providing a leak detection system inside the building, • Remove ignition sources from areas of the building where leaked hydrogen might accumulate, • Properly ventilate all enclosed spaces where leaked hydrogen might accumulate in the building, and • Provide warning to building employees and activate automatic safety systems in the event of a leak. These automatic safety systems may include rolling up bay doors automatically, increasing ventilation, and shutting down non-essential power systems and equipment (see Section 2.4). 5.1 DESIGN All facilities should have positive ventilation. Ventilation inlets should be at floor level and outlets should be at ceiling level. Typically at least five air changes per hour should be provided in maintenance facilities, while vehicle storage areas can have lower rates (local codes may vary). Facilities should have one or more hydrogen detectors located at ceiling level in the areas where vehicles will be fueled, maintained, or stored (see Figure 27). Figure 27. Hydrogen Detector Located at Ceiling Level Photo courtesy of California Fuel Cell Partnership. 60 These hydrogen detectors should be linked to an alarm system that will provide two levels of automatic alarm and action: Level 1 (typically when hydrogen is detected at 25 percent of lower flammable limit): • Shut off all hydrogen gas supplies (for fueling areas). • Sound an audible alarm heard in the area of the detector. • Flash red light(s) in the area of the detector. • Open maintenance bay doors. • Increase building ventilation rate to at least double the base rate. Level 2 (typically when hydrogen is detected at 50 percent of lower flammable limit): • Sound the fire alarm for building evacuation. • Automatically notify emergency or safety coordinator for the facility. • Disconnect all electrical power other than for alarms and ventilation fans. The structural system for the building’s roof/ceiling should not create pockets where leaked hydrogen gas can collect without being swept by the ventilation system. Electrical equipment, including lights, conduit, and wiring should not be located within eighteen inches of the ceiling. If equipment must be located in this zone (e.g., hydrogen detectors and ventilation fans), it must be sealed so that it is “explosion proof” (see Figure 28). Figure 28. Explosion Proof Switches Photo courtesy of Santa Clara Valley Transportation Authority. Building heating should be provided by forced hot air, hot water, steam, or other indirect methods. Air intakes should be properly located to avoid the intake of ventilated gas. Open flame heaters should not be located in the building. The building fire alarm system should include UV detectors to detect a hydrogen flame. If vehicles that store liquid hydrogen onboard will be maintained or stored in the facility, each maintenance bay or parking location should have a dedicated vent that can cover the outlet from 61 a vehicle’s pressure relief valves. These vents should be manifolded to a building stack vent. The top of the building stack should be higher than surrounding buildings and should vent into an open area with no overhanging wires or structures. The building stack should be equipped with a diffuser/flame arrester. 5.2 OPERATION AND MAINTENANCE Never bring a vehicle with a known hydrogen fuel leak into any building. Check and calibrate hydrogen sensors and UV flame sensors in accordance with the manufacturer’s service schedule. Regularly check the operation of the building’s hydrogen alarm system to ensure that the system automatically triggers the correct actions at each level of alarm. Train all employees on hydrogen safety in accordance with the Facility Safety Plan, and conduct regular fire/hydrogen alarm drills. PEM fuel cell engines and SOFC APUs that include a fuel reformer and which operate on liquid hydrocarbon fuels (i.e., methanol or diesel fuel) will emit carbon dioxide in their exhaust. The volume of exhaust and the amount of carbon dioxide emitted will be significantly less than the amount produced by a commercial vehicle’s main diesel engine while idling. Nonetheless, these devices should not be operated inside a closed building unless the exhaust outlet is connected to a system that vents the exhaust to the outside of the building. Carbon dioxide emitted into a poorly ventilated space can displace oxygen and result in asphyxiation. 5.3 FACILITY SAFETY PLAN For each building that will maintain or house hydrogen-fueled vehicles, the organization should develop a written Facility Safety Plan. This plan should include, at a minimum: • Schedule and procedures for calibration of the hydrogen detection/alarm system • Schedule and procedures for conducting a test of the hydrogen detection/alarm system • Schedule and procedures for conducting fire/hydrogen alarm drills for all building employees, and re-training whenever new equipment or new hazards are present • Instructions for what each employee should do in the event of a hydrogen alarm at each level of detection. • Rules regarding employee conduct, for example: – No smoking in the facility – Only specially trained employees should work on hydrogen fuel systems – No vehicles with known fuel leaks should be brought into the building unless defueled 62 63 • Maintenance practices related to hydrogen systems, for example: – Vehicles should be defueled before bringing them into the building for work on the hydrogen fuel system – Procedures to protect hydrogen components during welding and cutting – Vehicles with onboard liquid hydrogen should have pressure relief valves connected to the building vent at all times when in the building • Schedule and curriculum of hydrogen safety training for new employees and ongoing refresher training for existing employees. Provide training or re-training whenever a new hazard or new equipment posing a new hazard is introduced. All facility employees should be given initial and refresher training on hydrogen safety. Topics should include at a minimum: • General overview of hydrogen properties • Description of hydrogen detection/alarm system • Actions to take in the event of a hydrogen alarm 6. EMERGENCY RESPONSE FOR PERSONNEL ASSIGNED TO VEHICLES CARRYING HYDROGEN As discussed in chapter 2, hydrogen has significantly different physical and chemical properties from other motor fuels, such as diesel fuel and gasoline. Based on these characteristics, the response to an incident with a hydrogen-fueled vehicle or at a hydrogen fuel station will be different from the response to incidents involving other fuels. This chapter briefly describes issues relevant for response to hydrogen vehicle and fuel station incidents. 6.1 RESPONDING TO AN INCIDENT The vehicle operator may receive a visual and audible indication of a leak from the onboard hydrogen gas detection system, or he or she may smell or see smoke, indicating a potential fire. If the operator suspects a hydrogen gas leak or a fire of any kind, the operator should, if possible, stop the vehicle in a safe place away from potential ignition sources, such as elevated train tracks, and away from any overpasses where leaking gas might collect. The operator should shut off the vehicle and evacuate all passengers before calling for assistance. In response to an on-road incident with a hydrogen-fueled vehicle or at a hydrogen fueling station, always maneuver responding vehicles and keep personnel upwind of the incident. Any leaking hydrogen gas may be moved by the wind, especially if the vehicle or fuel station is carrying or storing liquid hydrogen. Commercial vehicles carrying hydrogen fuel can be identified by a blue diamond label on the rear and on either side of the power unit cab that will say either “Hydrogen,” “Compressed Hydrogen,” or “Liquid Hydrogen” (see Figure 16). Commercial trailers carrying hydrogen fuel (for example, to power a transportation refrigeration unit) should also be labeled with the blue diamond label on the rear and on either side in the vicinity of the hydrogen storage tanks. Look for signs of a hydrogen leak or fire. A large high-pressure hydrogen gas leak will likely produce a whistling sound, while leaking liquid hydrogen will likely be accompanied by an area of fog in the surrounding air and frost on equipment and lines in the vicinity of the leak. A hydrogen fire has a virtually invisible flame in daylight, but the heat given off may create a shimmer in surrounding air due to changes in air density or may ignite other nearby materials that will have a visible, smoky flame. A UV optical sensor, if available, can be used to search for signs of a hydrogen fire. Locate the vehicle’s PRD/TRD venting location (for compressed hydrogen) or the pressure relief valve venting location (for liquid hydrogen). These should be at vehicle roof level. Also locate the hydrogen storage tanks. These may be between the frame rails of the vehicle, in an enclosure behind the vehicle cab, or on the roof of the vehicle under a cowling. The hydrogen storage tanks and PRD/TRD location are the most likely locations for a hydrogen leak or fire. 64 If one must approach the vehicle, do so perpendicular to the hydrogen tanks, not directly in front of the ends of the tanks. If a compressed hydrogen cylinder was to fail, it would fail at the dome ends. If there is any question that there might be an undetected hydrogen fire, one can approach the vehicle with a corn straw broom extended and moving slowly back and forth. Any hydrogen fire will ignite the broom’s bristles. If safe to do so, shut down the vehicle by turning the ignition key. In all cases, this should close valves that will isolate the hydrogen in the storage tanks, shutting off the flow of hydrogen to any leaks in the fuel cell engine or hydrogen supply lines. Commercial vehicles may also have an emergency shutdown switch in the driver’s compartment and/or a battery disconnect switch accessible through a marked compartment door on the side of the vehicle. If so, turning either of these switches off should also isolate hydrogen in the hydrogen storage tanks. Even with the vehicle shut off, it is still possible for hydrogen to vent from a PRD/TRD (compressed hydrogen) or from a pressure relief valve (liquid hydrogen). It is impossible to stop the flow from a PRD/TRD once it has started; one must just wait for all of the hydrogen in the tanks to vent. Flow from a liquid hydrogen tank pressure relief valve will stop once the pressure inside the tank falls below a set value, but may start again if the tank pressure begins to rise (for example, if the tank is impacted by burning of adjacent materials, which will cause the tank temperature to rise). Hydrogen fuel cell vehicles are electric vehicles and high voltage (nominal 300–600 VDC) will always be present when the fuel cell is operating. High-voltage lines can be identified with orange coverings or markings. Some commercial fuel cell vehicles will be designed with a hybrid-electric drive configuration, in which case, a high-voltage battery or ultracapacitor pack will also be present on the vehicle. Shutting off the ignition switch and/or activating the emergency shutdown switch or throwing the battery disconnect switch should de-energize the fuel cell engine and all high-voltage lines. However, high voltage will always be present inside the battery or ultracapacitor pack (if included). Even if the system is off, one should never cut any hydrogen fuel line or high-voltage cable. One should never under any circumstances cut into a hydrogen storage tank or high-voltage battery pack. Commercial vehicles with a hydrogen-fueled ICE engine may also be designed with a hybridelectric drive configuration, in which case, a high-voltage battery or ultracapacitor pack and high-voltage lines will be present. As with fuel cell vehicles, shutting of the ignition switch on these vehicles should isolate hydrogen in the hydrogen storage tanks and isolate high voltage in the battery or ultracapacitor pack. 6.2 DETECTING HYDROGEN LEAKS Hydrogen is naturally odorless and colorless. The sulfur-based odorants typically used with natural gas and propane to aid in leak detection are incompatible with fuel cells and are not currently used with hydrogen. 65 Large leaks of hydrogen gas will likely have an audible hiss, and leaking liquid hydrogen will likely be accompanied by fog in surrounding air and frost on equipment and lines in the vicinity of the leak. Small hydrogen leaks can also be confirmed using a hand-held hydrogen sensor (see Figure 29). These devices use similar technology to the hydrogen sensors installed on fuel cell vehicles and at hydrogen fueling stations. Figure 29. Hydrogen Leak Detector Photo courtesy of B. Parsley. 6.3 HYDROGEN FIRES A hydrogen fire should not be extinguished with water or chemicals. Static electricity generated across the leak orifice, or an adjacent hot surface, could explosively reignite the leaking hydrogen. The best way to deal with a hydrogen fire is to shut off the flow of hydrogen gas by closing supply valves, which will extinguish the flame. If a small flame must be extinguished in order to gain access to a hydrogen supply valve, a dry-powder extinguisher is recommended (Air Products, 2004). The flow of hydrogen through a leaking PRD/TRD cannot be stopped. The best approach in this situation is to let the fire burn until all of the hydrogen has been consumed, while protecting surrounding vehicles and structures. If safe to do so, move nearby vehicles away from the hydrogen fire. Water sprays could help to keep surrounding equipment and structures cool. Use normal procedures to extinguish secondary fires ignited by the burning hydrogen and to deal with gasoline or diesel fuel spilled from other vehicles involved in the incident. Be aware of the PRD/TRD outlet locations from uninvolved hydrogen tanks. If a loud hissing is heard, move away. See Figure 30, which shows a simulation of a fire in a hydrogen-fueled vehicle (SAE, 2006). In this test, a fire was intentionally started in the driver’s ashtray, which spread through the vehicle 66 cabin. After approximately 15 minutes, a PRD on one of two trunk-mounted compressed hydrogen storage cylinders activated due to an increase in the temperature in the trunk to above 230 °F. In the photo on the left, flames from ignited hydrogen released through the PRD can be seen rising above the vehicle. After approximately 15 seconds, virtually all of the hydrogen had vented from both storage cylinders, but the cabin fire was still burning (right photo). In this test, the maximum height of the hydrogen flames was higher than the maximum height of flames during a similar test of a gasoline-fueled vehicle, but the gasoline-fueled flames were wider and persisted longer (from growing to diminishing flame). Radiated heat levels around the vehicle were also lower for the hydrogen-fueled fire than for the gasoline-fueled fire, and total damage to the vehicle was less (though in both cases it was significant). This is only one of many vehicle fire scenarios, but is illustrative of the differences between hydrogen-fueled fires and those fueled by gasoline or diesel fuel. Figure 30. Hydrogen Vehicle Fire Showing Ignited Hydrogen Released from PRD 6.4 LIQUID HYDROGEN Leaking liquid hydrogen poses a severe frostbite hazard to exposed skin. As it warms, liquid hydrogen will vaporize and create a cloud of cold hydrogen gas above the liquid puddle. This cloud may move sideways before rising as the gas warms further, and may extend beyond the area of accompanying fog. This cold hydrogen gas also poses a frostbite hazard and all personnel should stay upwind of the leak site. As with gaseous hydrogen, the best approach to dealing with leaked liquid hydrogen that has ignited is to shut off the source of the leak if possible, protect surrounding structures and equipment, and let it burn until all of the hydrogen has been consumed. Never spray water onto a liquid hydrogen tank. If it is venting, the water could freeze and plug the tank’s pressure relief valve, resulting in excessive pressure and possible rupture of the tank. 67 68 While leaked liquid hydrogen is unlikely to travel far before vaporizing, the liquid should not be allowed to enter a storm sewer or other underground structure. This could result in a severe fire and explosion hazard as the hydrogen vaporizes and mixes with air in the enclosed space. APPENDIX A: OPERATION OF A FUEL CELL PEM FUEL CELL A PEM fuel cell is generally constructed from a series of thin layers of different materials, each with a different function, that are stacked together. These include a metal or graphite flow plate on either side of the device, each covered with a layer of porous carbon fiber paper. Each flow plate has grooves cut into it to distribute either hydrogen or oxygen across the carbon fiber paper. Between the layers of carbon fiber paper is a thin plastic-like film, called a “proton exchange membrane,” which is coated on both sides by a platinum-based catalyst (see Figure 31). Air Flow Plate Proton Exchange Membrane Hydrogen Flow Plate Carbon Fiber Paper (anode) Carbon Fiber Paper (cathode) Air Flow Plate Proton Exchange Membrane Hydrogen Flow Plate Carbon Fiber Paper (anode) Carbon Fiber Paper (cathode) Figure 31. PEM Fuel Cell Construction The hydrogen fuel flows through the flow plate on one side of the device, while air flows through the flow plate on the other side of the device. The two layers of carbon fiber paper act as the anode (hydrogen side) and cathode (air side) of the fuel cell. The anode and cathode are connected together electrically to form an electrical circuit. One or more electrical loads, such as an electric motor, are connected to this external circuit. The proton exchange membrane acts as the electrolyte in the galvanic fuel cell. Because both the anode and the cathode are porous, they allow the hydrogen and air to contact either side of the proton exchange membrane, but the two gas streams do not mix. At the surface of the membrane, the platinum catalyst causes the electron in each hydrogen atom that contacts it to separate from the atom’s nucleus—leaving a proton, or hydrogen ion. While a hydrogen atom cannot pass through the membrane, a proton can. In fact, the protons are drawn through the proton exchange membrane to the cathode on the other side. In the meantime, the separated electrons flow along the anode and through the external electrical circuit. This flow of electrons is electricity, which is put to work by the devices connected to the circuit. 69 When two protons reach the cathode they combine, in the presence of the platinum catalyst, with one oxygen atom and two electrons flowing into the cathode from the electrical circuit, creating a molecule of water (H2O). This water, along with the electricity flowing through the circuit and a small amount of heat, are the only by-products of the reaction. See Figure 1, which shows the operation of a PEM fuel cell. For additional information, see the following websites that include both descriptions and animations of fuel cells in operation: http://www.humboldt.edu/~serc/animation.html http://www.howstuffworks.com/fuel-cell.htm http://www.fuelcells.org/basics/how.html SOFC FUEL CELL Like PEM fuel cells, solid oxide fuel cells (SOFCs) are galvanic cells that directly produce electricity from hydrogen and oxygen through an electrochemical reaction. However, SOFCs are constructed of different materials and use a different chemical reaction from PEM fuel cells. In an SOFC, the electrolyte is not a plastic-like material—it is a ceramic material made of a solid metal oxide, usually zirconium oxide. This electrolyte does not need to be coated with an expensive platinum catalyst as in a PEM cell. Rather than passing positively charged hydrogen ions (i.e., protons) across the electrolyte from the anode to the cathode, an SOFC passes negatively charged oxygen ions (O-2) in the other direction, from the cathode to the anode. Electrons are still passed from the anode to the cathode through an external circuit, and the major by-product of the reaction is water, which collects at the anode (see Figure 6). SOFCs are generally constructed differently than PEM cells as well. Rather than being built by stacking separate material layers, they are often built like computer chips by chemically depositing thin layers of the different materials required (College of the Desert, 2001c). They can be built either with a flat plate design or with a tubular design. In a tubular design, the zirconium oxide is deposited onto the outside of porous supporting tubes and the air is directed through the middle of the tubes, while the fuel is distributed around the outside of the tubes (see Figure 32). 70 71 Figure 32. SOFC Construction Tubular Design Source: College of the Desert, 2001c. Unlike a PEM cell, an SOFC does not need to be fueled with pure hydrogen gas. Because SOFCs operate at such high temperatures and because oxygen ions are transferred through a solid oxide electrolyte material—not hydrogen ions—SOFCs support automatic “reforming” of gaseous hydrocarbon fuels, such as methane (natural gas), within the device. Reforming is the chemical process of separating the hydrogen from the carbon atoms in a hydrocarbon fuel. If combined with a relatively simple fuel reformer/processor, diesel fuel or gasoline can also be used to fuel an SOFC. The reformate produced by the fuel processor, which will include hydrogen, carbon dioxide, carbon monoxide, and nitrogen, is introduced as the fuel at the anode. In this case, the exhaust from the SOFC will include CO2 and nitrogen, as well as water and heat. SOFCs operate at much higher temperatures than PEM fuel cells—between 600°F and 1,000°F—so the waste heat created during operation is also at a higher temperature and can therefore more easily be put to use, for example, to heat the interior of a vehicle as is typical of the waste heat from an ICE. APPENDIX B: CODES AND STANDARDS AND RECOMMENDED PRACTICES Regulations are legal requirements established by relevant government agencies or oversight organizations. Codes are guidelines for the design of the built environment and are generally adopted by local jurisdictions. Standards are rules, guidelines, or characteristics for equipment, components, or processes often promulgated by industry organizations. Standards may be voluntary or may be enforced when referenced in codes or government regulations. The precedent for establishing system safety programs for new technologies and operations has a long history in several industries (e.g., military, commercial aircraft, petrochemical, and public transit). The commercial use of hydrogen in vehicle applications is in its infancy, and the development of applicable codes and standards is ongoing. Although currently there are few specific regulations or codes for design and operation of hydrogen fueled vehicles, there are a number of applicable standards, guidelines, and recommended practices developed by the National Fire Protection Association and the Society for Automotive Engineers. Some of these requirements have been included in state-level building codes. The remainder of this chapter discusses existing standards and codes applicable to hydrogen vehicles and facilities. FEDERAL REGULATIONS U.S. federal regulations associated with vehicles, systems, and equipment are contained in the Code of Federal Regulations (CFR). Depending on the type of vehicle, transportation mode, or subject, different federal agencies have responsibility to develop and oversee these regulations. The following is a list of CFR regulations that pertain to different types of vehicles, as well as different aspects of hydrogen production and use, along with the agency responsible for them. In some cases, these regulations have requirements specific to hydrogen operations. In other cases, they are general regulations applicable to all vehicles, with no specific reference to or requirements associated with hydrogen use. • Trucks It is important to note that hazardous materials carried on a vehicle for the purpose of supporting the operation or maintenance of that vehicle including its auxiliary equipment are exempt as "materials of trade" from the hazardous materials regulations (see 49 CFR 171.8 and 173.6). Examples of such hazardous materials include fuel for propulsion or auxiliary power units, electrolyte for batteries, and chemicals (e.g., urea) for selective catalytic reduction. Otherwise, hazardous materials carried as cargo on a vehicle are subject to the hazardous materials regulations at 49 CFR Parts 171-180. While not subject 72 to regulation by the Pipeline and Hazardous Materials Safety Administration, the U.S. Department of Transportation modal administrations (such as FMCSA) may subject to regulation the "materials of trade" as well as the vehicle systems that they support. – 49 USC 31136 and 31502(b), 49 CFR Subpart E (Safety standards for commercial motor vehicles fuel systems) – 42 USC 7521-7590, 40 CFR Parts 80, 85, 86 (EPA) (Control of air pollution from new and in-use motor vehicles and engines) – 49 USC 30101 et seq., 49 CFR Pts. 501-596, Working Part 29 (NHTSA) (Safety standards for all motor vehicles) – Responsible Oversight Agencies: EPA, FMCSA, NHTSA • Buses It is important to note that hazardous materials carried on a vehicle for the purpose of supporting the operation or maintenance of that vehicle including its auxiliary equipment are exempt as "materials of trade" from the hazardous materials regulations (see 49 CFR 171.8 and 173.6). Examples of such hazardous materials include fuel for propulsion or auxiliary power units, electrolyte for batteries, and chemicals (e.g., urea) for selective catalytic reduction. Otherwise, hazardous materials carried as cargo on a vehicle are subject to the hazardous materials regulations at 49 CFR Parts 171-180. While not subject to regulation by the Pipeline and Hazardous Materials Safety Administration, the U.S. Department of Transportation modal administrations (such as FMCSA) may subject to regulation the "materials of trade" as well as the vehicle systems that they support. – 42 USC 7521-7590, 40 CFR Parts 80, 85, 86 and 88 (EPA) (Control of air pollution from new and in-use motor vehicles and engines) – 49 USC 5121, 49 USC 31136 and 31502(b), 49 CFR Subpart E (FMCSA) (Safety standards for commercial motor vehicles) – 49 USC 30101 et seq., 49 CFR Pts. 501-596, Working Part 29 (NHTSA) (Safety standards for all motor vehicles) – Responsible Oversight Agencies: EPA, FMCSA, NHTSA • Fuel Cell Siting and Hydrogen Production, Distribution, Storage, Use, Dispensing, and Disposal – 49 USC 5101 et seq., 49 CFR Pts. 171-180 (PHMSA) (Hazmat transportation, packaging, and inspection) – Responsible Oversight Agencies: EPA, PHMSA • Occupational Safety and Health Administration (OSHA) – 29 CFR §1910.38, Emergency action plans, provides for the content of an emergency action plan when an emergency action plan is required by another standard. – 29 CFR §1910.103, Hydrogen, contains requirements for hydrogen systems. – 29 CFR §1910.132(a), Personal protective equipment, requires that protective equipment, including personal protective equipment for eyes, face, head, and extremities, protective clothing, respiratory devices, and protective shields and barriers, shall be provided, used, and maintained in a sanitary and reliable condition wherever necessary. 73 – 29 CFR §1910.156, Fire brigades contains requirements for the organization, training, and personal protective equipment of fire brigades whenever they are established by an employer. The requirements under 1910.156 apply to fire brigades, industrial fire departments and private or contractual type fire departments. Personal protective equipment requirements contained in this section apply only to members of fire brigades performing interior structural firefighting. – 29 CFR §1910.1200, Hazard communication requires that hazards associated with hydrogen must be conveyed to employees. In addition, the standard requires that the information be transmitted through a comprehensive hazard communication program, including, but not limited to, container labeling, material safety data sheets, and employee training on the hazards associated with handling hydrogen. – Responsible Oversight Agencies: OSHA NATIONAL FIRE PROTECTION ASSOCIATION STANDARDS The National Fire Protection Association (NFPA), established in 1896, serves as the world's leading advocate of fire prevention and is an authoritative source on public safety. One of the activities of the NFPA is to develop codes and standards to enhance fire safety. The codes serve a wide range of applications, from general fire building codes to specific applications. The following is a list of NFPA codes that are applicable to hydrogen facilities: • NFPA 101 – Life Safety Code (Applicable to maintenance facility design) • NFPA 70 – National Electric Code (Applicable to maintenance facility design) • NFPA 30A – Code for Motor Fuel Dispensing Facilities and Repair Garages (Applicable to maintenance and vehicle storage facility design) • NFPA 50A – Gaseous Hydrogen Systems at Consumer Sites (Applicable to refueling and fuel storage facility design) • NFPA 50B – Liquefied Hydrogen Systems at Consumer Sites (Applicable to refueling and fuel storage facility design) • NFPA 52 – Vehicular Fuel Systems Code (Applicable to vehicle fuel systems in general, not specific for hydrogen) • NFPA 55 – Compressed and Liquefied Gases in Portable Cylinders (includes NFPA 50A and 50B) (Applicable to refueling and fuel storage facility design) • NFPA 88 – Standard for Parking Structures (Applicable to vehicle storage facility design) COMPRESSED GAS ASSOCIATION Since 1913, the Compressed Gas Association (CGA) has been dedicated to the development and promotion of safety standards and safe practices in the industrial gas industry. It is due to the efforts of the CGA that the industry has remained largely self-regulating throughout the 74 twentieth century. More than 200-member companies worldwide work together through the committee system to create technical specifications, safety standards, and training and educational materials; to cooperate with governmental agencies in formulating responsible regulations and standards; and to promote compliance with these regulations and standards in the workplace. The following is a list of CGA standards applicable to hydrogen: • CGA G-5.4 – Standard for Hydrogen Piping Systems at Consumer Locations Edition 3, February 18, 2005 (Applicable to refueling and storage facility design) • CGA G-5.5 – Standard for Hydrogen Vent Systems Edition 2, April 20, 2004 (Applicable to refueling and storage facility design) • CGA G-5.6 – Standard for Hydrogen Pipeline Systems Edition 1,May 12, 2005 (Applicable to refueling and storage facility design) • CGA H-2 – Guidelines for the Classification and Labeling of Hydrogen Storage Systems with Hydrogen Absorbed in Reversible Metal Hydrides Edition 1, April 24, 2004 (Applicable to refueling and storage facility design) • CGA H-3 – Standard for Cryogenic Hydrogen Storage Edition 1, March 14, 2006 (Applicable to refueling and storage facility design) • CGA C-6.4 – Methods for External Visual Inspection of Natural Gas Vehicle (NGV) Fuel Containers & Their Installations (Applicable to refueling and storage facility design) SOCIETY OF MECHANICAL ENGINEERS (ASME) STANDARDS Founded in 1880 as the American Society of Mechanical Engineers, ASME sets internationally recognized industrial and manufacturing codes and standards that enhance public safety. The following is a list of ASME standards and guidelines applicable to hydrogen: • ASME – Boiler and Pressure Vessel Code - 2007 Edition 2005 (Applicable to fuel storage system design) • 2006 Design Factor Guidelines for High-Pressure Composite Hydrogen Tanks (Applicable to fuel storage system design) • 2005 Hydrogen Standardization Interim Report for Tanks, Piping, and Pipelines (Applicable to fuel storage system design) SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) STANDARDS The Society of Automotive Engineers (SAE) develops standards and recommended practices for the design, operation, and maintenance of automotive systems and equipment. The following is a list of SAE publications that are applicable to hydrogen: • SAE J2574 – Fuel Cell Vehicle Terminology • SAE J2600 – Compressed Hydrogen Surface Vehicle Refueling Connection Devices 75 76 • SAE J2760 – Pressure Terminology Used in Fuel Cell and Other Hydrogen Vehicles • SAE J2594 – Fuel Cell Recyclability Guidelines • SAE J 2578 – Recommended Practice for General Fuel Cell Vehicle Safety • SAE J1766 – Post Vehicle Collision Electrical Energy Storage Safety INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) The International Organization for Standardization (ISO) is the world's largest developer of standards. ISO is a network of the national standards institutes of 157 countries, on the basis of one member per country, with a Central Secretariat in Geneva, Switzerland, that coordinates the system. ISO standards are voluntary. As a nongovernmental organization, ISO has no legal authority to enforce their implementation. A certain percentage of ISO standards, mainly those concerned with health, safety, or the environment, has been adopted in some countries as part of their regulatory framework or is referred to in legislation for which it serves as the technical basis. ISO standards that pertain to hydrogen are: • ISO Standard 13985, dated November 1, 2006 - Liquid hydrogen - Land vehicle fuel tanks (Applicable to fuel storage system design) • ISO Standard 21012, dated November 15, 2006 - Cryogenic vessels – Hoses (Applicable to fuel storage system design) • ISO Standard 15916, dated February 15, 2004 – Basic Considerations for the Safety of Hydrogen Systems (Applicable to hydrogen system safety) GLOSSARY Catalyst – A material that increases the rate of a chemical reaction without itself being consumed in the reaction. A proton exchange membrane fuel cell requires a platinum-based catalyst to drive the chemical reactions between hydrogen and oxygen in the cell. Combustion – High-temperature oxidation of a fuel (i.e., burning) which releases heat and light. Cryogenic Liquid – Any liquid whose temperature is below -100 °C. Cryotank – A well-insulated container used to store a cryogenic liquid. Also called a “cryogenic vessel” or a “dewar.” Diffuser – A device designed to reduce the concentration of a gas (such as hydrogen) by mixing with air. Electrolyzer – A galvanic cell composed of an anode and a cathode submerged in a water-based electrolyte, used to separate water into hydrogen gas and oxygen gas through the application of an electric current. Fail Safe – Design in which a device or system will be put into the safest possible condition if the device or system fails. For example, an electrical switch that requires a signal voltage to stay closed; if the signal is lost due to a failure, the switch is designed to open and cut off the flow of electricity. Fuel Cell – A galvanic cell that uses an electrochemical reaction to directly produce electricity from the oxidation of hydrogen. In a fuel cell, hydrogen is the anode material and oxygen is the cathode material (see Galvanic Cell). Fuel Cell Engine – A device that combines one or more fuel cells with support systems to create a practical device for producing electrical power from hydrogen fuel. In addition to the fuel cells themselves, a fuel cell engine will typically require a fuel delivery system, an air system, a cooling system, and a water handling system. Galvanic Cell – A device composed of an anode, a cathode, and an electrolyte. An electrochemical reaction between the anode and cathode materials causes electrical current to flow in a circuit connecting the anode and cathode. As part of the reaction, ions are transported across the electrolyte between the anode and cathode. Green House Gas – Gaseous components of the earth’s atmosphere that cause heat from the sun to be trapped, thus warming the earth. The most abundant man-made green house gas is carbon dioxide, produced during combustion of hydrocarbon fuels. Ground (electrical) – A physical conductive connection between a device and a reference point (such as a vehicle chassis). The connection provides a path for electric current to flow, ensuring that the device will be at the same electrical potential as the reference, so that an electrical charge that might cause a spark cannot build up. 77 78 Hazardous Voltage – Any voltage that can harm a human through electric shock. Any voltage greater than 30 VAC or 60 VDC is considered a “hazardous voltage.” Hybrid-Electric Drive System – A hybrid electric drive system is one that uses two distinct power sources to provide propulsion power, for example, an internal combustion engine and a battery pack, or a fuel cell engine and a battery pack. In a hybrid-electric drive system, power from the battery pack supplements the engine when peak power is required (during acceleration) so the engine does not need to be as large as it would be in a conventional drive system. The battery can also be used to store power generated during braking for later use. In a conventional drive system, all braking energy is wasted. The use of a hybrid-electric drive system increases overall fuel efficiency, especially in stop-and-go driving. Hydride – A compound of hydrogen with other elements. Both solid metal hydrides and chemical hydrides can be used to store hydrogen fuel for a fuel cell vehicle. In a solid metal hydride, the hydrogen is absorbed onto the surface or into the crystalline lattice of the metal. In a chemical hydride (for example, sodium borohydride), the hydrogen is chemically bound to other elements. Hydrocarbon – A chemical compound that consists only of the elements hydrogen and carbon. Various hydrocarbons are the main components of all fossil fuels, including gasoline, diesel fuel, and natural gas. Hydrogen Embrittlement – The process by which a metal becomes brittle and develops small cracks due to exposure to hydrogen. Ion – An atom, normally electrically neutral, that gains an electrical charge by gaining or losing one or more electrons. A positive ion is an atom that has lost one or more electrons and a negative ion is one that has gained one or more electrons. Lower Flammable Limit – The lowest concentration at which a mixture of a gas in air can burn. The lower flammable limit for hydrogen is 4 percent by volume at room temperature and atmospheric pressure. If less than four percent hydrogen is present, the mixture will not burn. millijoule – One-thousandth of a joule. A joule is a unit of work or energy. One millijoule is the amount of energy required to lift up an object that weighs 1 gram to a height of 10 centimeters. Proton Exchange Membrane Fuel Cell – A type of low-temperature hydrogen fuel cell that uses a proton exchange membrane electrolyte, which passes hydrogen ions from the anode to the cathode. PEM fuel cells must be fueled with pure hydrogen gas. PEM fuel cells are the most common type of fuel cell used to power vehicles. Reforming – A chemical process that converts a liquid or gaseous hydrocarbon fuel, such as diesel fuel or natural gas, into a hydrogen-rich gas. Reformate – The product of reforming a hydrocarbon fuel. Depending on the fuel and the process used, reformate will be anywhere from 40 to 75 percent hydrogen by volume, with the remainder carbon dioxide, nitrogen, and water vapor. REFERENCES Air Products and Chemicals, Inc. 1999. Safetygram #15 Cylinder Pressure Relief Devices, 310- 726 (rev 9/99). ———. 2004. Safetygram #4 Gaseous Hydrogen, 23771. Amerada Hess Corporation. 2001. Material Safety Data Sheet, Low Sulfur Diesel Fuel, MSDS No. 9904, Revision Date February 28, 2001. Argonne National Laboratory. 2003. Environmental, Safety and Health Manual-ANL-E, July 1, 2003. Barnitt, Robb, Eudy, Leslie, and U.S. Department of Energy. 2005. Energy Efficiency & Renewable Energy, Overview of Advanced Technology Transportation, 2005 Update, DOE/GO-102005-2117, August 2005. California Fuel Cell Partnership. 2006. Fuel Cell Cars. Available at: www.fuelcellpartnership.org/fuel-vehl_cars.html. California Hydrogen Highway Network. 2004. Hydrogen Internal Combustion Engine (ICE) Vehicles. Available at: www.hydrogenhighway.ca.gov/vehicles/ice.htm, updated April 16, 2004. Accessed December 6, 2006. Canadian Hydrogen Energy Company. 2006. Hydrogen Fuel Injection. Available at: www.chechfi.ca/index.html. Chandler, Kevin, and Eudy, Leslie, and U.S. Department of Energy, National Renewable Energy Laboratory. 2006. Santa Clara Valley Transportation Authority and San Mateo County Transit District Fuel Cell Transit Buses: Evaluation Results, Table 2, Technical Report NREL/TP-560-40615, November 2006. College of the Desert, Energy Technology Training Center. 2001a. Hydrogen Fuel Cell Engines and Related Technologies, Module 2: Hydrogen Use, Revision 0, December 2001; interpolation of data in figure 2-19, Storage Volume and Weight of Comparative Fuels Each with 990,000 BTU of Stored Energy. ———. 2001b. Hydrogen Fuel Cell Engines and Related Technologies, Module 3: Hydrogen Use in Internal Combustion Engines, Revision 0, December 2001. ———. 2001c. 15, Hydrogen Fuel Cell Engines and Related Technologies, Module 4: Fuel Cell Technology, Revision 0, December 2001. Compressed Gas Association, Inc. 1984. Pamphlet C-6: Standards for Visual Inspection of Compressed Gas Cylinders. 79 Delphi Energy Systems. 2005. Product Brochure, Delphi Solid Oxide Fuel Cell: Auxiliary Power Unit. EG&G Technical Services, Inc. (under contract to U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory). 2004. Fuel Cell Handbook (7th ed.), November. ETV Canada, Environmental Technology Verification (ETV) Program. June 2005. Hydrogen Fuel Injection System Technology Fact Sheet for Canadian Hydrogen Energy Company Ltd. Available at: www.etvcanada.com/graduates.asp. Accessed December 22, 2006. Georgetown University. October 2003. The Georgetown X-1 Fuel Cell Bus IN DEPTH. Available at: www.fuelcellbus.georgetown.edu/x1desc.cfm. Accessed September 19, 2006. Hydrogen Analysis Resource Center, U.S. Department of Energy. November 2004. Solid Oxide Fuel Cell Manufacturers. Available at: http://hydrogen.pnl.gov/cocoon/morf/hydrogen. Accessed December 19, 2006. Linde Group Gas & Engineering, n.d. LNG and LH2 Technology for Vehicles. Available at: http://www.linde-anlagenbau.de/en/p0001/p0043/p0043.jsp. Accessed December 1, 2005. Murphy, Michael J., Ketola, Norman H., and Raj, Phani K. August 1995. Clean Air Program Summary of Assessment of the Safety, Health, Environmental and System Risks of Alternative Fuels, U.S. Department of Transportation, Federal Transit Agency, FTA-MA- 90-7007-95-1, DOT-VNTSC-FTA-95-5. NEWCARS. 2003. Ford U Concept. Available at: www.new-cars.com/concept/2003/ford-uconcept.html. Accessed December 5, 2006. National Fire Protection Association. August 2005. Vehicular Fuel Systems Code, 2006 Edition. Parsons Brinckerhoff, in association with TIAXX and the University of Miami. July 2004. Support Facilities for Hydrogen Fueled Vehicles Conceptual Design and Cost Analysis Study, CaFCP Commissioned Technical Report. Raj, Phani K, Technology & Management Systems, Inc, for U.S. Department of Transportation, Federal Transit Agency. October 1998. Clean Air Program: Design Guidelines for Bus Transit Systems Using Hydrogen as an Alternative Fuel, DOT-FTA-MA-26-7021-98-1. Ringland, J. T. March 1994. Safety Issues for Hydrogen Powered Vehicles, Report No. SAND94-8226.UC-407, NTIS No. DE94-008909, Sandia National Laboratory. Society of Automotive Engineers (SAE). December 2002. J2578 –Recommended Practice for General Fuel Cell Vehicle Safety, Section 4.7. ———. January 1997. J2343 – Recommended Practices for LNG Powered Heavy-Duty Trucks. 80 81 ———. 2006. SAE 2006-01-0129, Fire Safety Evaluation of a Vehicle Equipped with Hydrogen Fuel Cylinders, Comparison with Gasoline and CNG Vehicles. Speer, Nate. February 8, 2004. How Hydrogen Sensors Work, Hydrogen and Fuel Cell Safety Report (The National Hydrogen Association). Available at: www.hydrogensafety.info/old/articles/04-feb-08.asp. Accessed September 20, 2006. U.S. Department of Energy (DOE). n.d. Hydrogen, Fuel Cells & Infrastructure Technologies Program, Storage Technologies. Available at: www.eere.energy.gov/hydrogenandfuelcells/storage/. Accessed September 19, 2006. ———. February 2002. A National Vision of America’s Transition to a Hydrogen Economy – To 2030 and Beyond. ———. February 2003. Fuel Cell Report to Congress, ESECS EE-1973. ———. 2006. Hydrogen, Fuel Cells & Infrastructure Technologies Program, Types of Fuel Cells. Available at: www.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html. Accessed September 19, 2006. U.S. Environmental Protection Agency (EPA), Office of Air and Radiation. October 2002. Study of Exhaust Emissions from Idling Heavy-Duty Diesel Trucks and Commercially Available Idle-Reducing Devices, EPA420-R-02-025. U.S. Fuel Cell Council and Fuel Cells (USFCC). 2000. Fuel Cell Vehicles (from Auto Manufacturers), data table, updated 12/06. Available at: www.fuelcells.org/info/charts/carchart.pdf.

[hydrogenfuelsystems-blog]

GUIDELINES FOR USE OF HYDROGEN FUEL IN COMMERCIAL VEHICLES

[hydrogenfuelsystems-blog]

Gen 10 Gen 15 and Gen 20 hydrogen generator systems for  cars trucks , generators and Trawlers

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NASA report  -  “Emissions and total energy consumption of a multicylinder piston engine burning Gasoline and hydrogen-gasoline mixture”   1977

fuel savings reports NASA 1977

http://www.hho4free.com/documents/nasa_hho_proof.pdf

[hydrogenfuelsystems-blog]

Lund Institute of technology report 2012   -   “hydrogen addition form improved lean burn capability

http://www.hho4free.com/documents/Hydrogen-addition_leanICE_hho_works.pdf

[hydrogenfuelsystems-blog]

Onboard Hydrogen generator for partial hydrogen injection Internal combustion engine  - California Institute of technology report

http://www.hho4free.com/documents/Hydrogen_reformation_generator.pdf

[hydrogenfuelsystems-blog]

The Effects of Hydrogen Addition to DieselFuel on the Emitted Particulate Matters

Government report into hydrogen addition with  diesel fuels  --

http://www.researchgate.net/publication/279549881_The_Effects_of_Hydrogen_Addition_to_Diesel_Fuel_on_the_Emitted_Particulate_Matters

[hydrogenfuelsystems-blog]

Towards development of an Australian scientific roadmap for the hydrogen economy

https://www.science.org.au/sites/default/files/user-content/hydrogen.pdf

[hydrogenfuelsystems-blog]

HYDROGEN INJECTION INTO DIESEL ENGINES FOR FUEL EFFICIENCY IMPROVEMENT - Murdoch University research report

i HYDROGEN INJECTION INTO DIESEL ENGINES FOR FUEL EFFICIENCY IMPROVEMENT Jacob Young (B.Eng) For: Murdoch University Division of Science and Engineering School of Energy Studies PEC624: Master of Science in Renewable Energy Dissertation, 2008 ii Declarations The content of this dissertation is the product of many hours of the authors time spent problem-solving, testing, and summarizing, unless otherwise noted. Acknowledgements The author would like to thank Tyrell Hedlund for the provision of tools, test space, and enthusiasm especially during the early period of testing. Also, the contributions of Aleksandra, Dr. Trevor Pryor, Dr. Philip Jennings was appreciated. The patience of my neighbours deserves recognition as well. iii Abstract The purpose of this investigation was to determine whether hydrogen injected into a diesel internal combustion engine has the potential to reduce overall fuel consumption. The most economical means of performing the required tasks was used whenever possible in an attempt to mimic a small off-grid application. The genset was a small 4kW compression ignition diesel. The electrolyzer was an off-the-shelf model designed for automotive applications. It combines hydrogen and oxygen output and is currently found from many manufacturers over the internet. It was found that the H2/02 mixture actually did help conserve fuel by about 18% in a low load case but generally, savings were under 5%. At a higher proportion of generator rated load, fuel consumption was shown to increase with H2/02 injection by up to 5%, thus the H2/02 output must be optimized to achieve any savings. Reasons for this phenomenon are discussed and recommendations for further research are included. iv Table of Contents Introduction .................................................................................................................................................1 Background .............................................................................................................................................1 Theory.......................................................................................................................................................2 Equipment Description ..........................................................................................................................5 Diesel Generator.................................................................................................................................5 Hydrogen/oxygen Electrolytic cell (Hydrogen Generator)............................................................5 Power Supply ......................................................................................................................................7 Measuring Instruments .....................................................................................................................7 Loads....................................................................................................................................................7 Primary Experimental Procedure.............................................................................................................7 Purpose................................................................................................................................................7 Equipment ...........................................................................................................................................7 Set up...................................................................................................................................................8 Procedure ............................................................................................................................................8 Analysis................................................................................................................................................9 Sources of Error..................................................................................................................................9 Early Findings ....................................................................................................................................... 10 Secondary Experimental Procedure ..................................................................................................... 10 Purpose............................................................................................................................................. 10 Equipment ........................................................................................................................................ 10 Set up................................................................................................................................................ 10 Procedure ......................................................................................................................................... 10 Analysis............................................................................................................................................. 11 Results....................................................................................................................................................... 11 Optimization Phase............................................................................................................................. 14 10 Ampere Load.............................................................................................................................. 14 14 Ampere Load.............................................................................................................................. 16 20 Ampere Load.............................................................................................................................. 17 23 Ampere Load.............................................................................................................................. 19 Discussion................................................................................................................................................. 22 Significance of Results ....................................................................................................................... 22 Limitations............................................................................................................................................ 25 Achievements ...................................................................................................................................... 25 Conclusion ................................................................................................................................................ 26 Opportunities........................................................................................................................................ 27 Lessons Learned.................................................................................................................................. 27 References................................................................................................................................................ 29 v Table of Figures Figure 1: H2/02 generator section cut .....................................................................................................6 Figure 2: Generator/weight measurement set up ................................................................................8 Figure 3: Process Efficiency at 20 Amp Load with Temperature interference.............................. 13 Figure 4: 10 Amp Load - Optimization .................................................................................................14 Figure 5: Process Efficiency at 10A Load ............................................................................................ 15 Figure 6: 14 Amp load – Optimization.................................................................................................16 Figure 7: Process Efficiency at 14A Load ............................................................................................ 17 Figure 8: 20 Amp load – Optimization................................................................................................ 18 Figure 9: Process Efficiency at 20 A Load ........................................................................................... 18 Figure 10: 23 Amp load – Optimization .............................................................................................. 19 Figure 11: Approximation of air fuel ratio for Amico engine............................................................ 20 Figure 12: Comparison of Baseline and Minimum H2/02 injected SFC.......................................... 24 Table of Equations Equation 1: Temperature compression ratio relation...........................................................................3 Equation 2: Thermal efficiency for Otto Cycle........................................................................................3 Equation 5: Percent error for measurements ........................................................................................9 Equation 6: Calculation of percent fuel savings ................................................................................. 12 Equation 7: Process Efficiency calculations ........................................................................................ 12 Equation 8: Air usage of Amico engine................................................................................................ 20 Equation 9: Electrolysis reagents.......................................................................................................... 21 Equation 10: Calculation of volumetric flows of electrolyzer ........................................................... 21 1 Introduction Background Diesel engines have a significant social, environmental, and economic impact that is readily evident to most people on Earth. Food consumed every day by many people today has been produced by the use of diesel fuel. Tractors used to work the soil and harvest crops, irrigation pumps to sustain them, and transport trucks to deliver them, primarily use diesel fuel. With a growing population, minimal options, and dwindling fossil fuel resources, diesel conservation should be a priority or malnutrition may result in many areas. Fossil fuel combustion releases greenhouse gases and particulates which are harmful to humans and the environment. The rapid rise of CO2 levels in the atmosphere in recent years is directly attributable to the combustion of fossil fuels1. There is evidence that rising CO2 levels can lead to climate change1. On a local scale, particulates from engine exhaust may cause health problems. No economy is immune to the effect of diesel fuel. Manufacturers use diesel to transport raw materials and finished products as well as to generate electricity. It may be argued that the global economy would cease to function without diesel fuel. The main contribution of this investigation is to reduce diesel fuel consumption which could have far reaching social, environmental, and economic benefits. Additionally, this investigation provides the opportunity to encourage development in renewable energy, specifically, integrating hydrogen generation in wind diesel grids. Hydrogen can be the energy storage that balances the wind output and load fluctuations when coupled with either a fuel cell or diesel generator. At the same time, hydrogen in renewable energy dominated grids can encourage the transition to hydrogen transport. If positive results occur, it may be feasible to extend the efficiency gains into all fossil fuel, or biomass combustion equipment such as heaters, cooking equipment, gas turbines, and gasoline/petrol engines. 1 Hunter, R 2 Theory Supplemental hydrogen injection was considered for fuel efficiency improvement for this investigation on account of its beneficial combustion characteristics, ease of use, and economic production. Currently, there exists much debate over the effects of supplemental hydrogen in internal combustion engines. This was another motivator to verify and quantify any efficiency improvements as claimed by some manufacturers2,3,4,5. The following summary of hydrogen properties with respect to internal combustion engines (ICEs) is derived from a training module for hydrogen engine technicians prepared by the College of the Desert and presented on the Department of Energy, Energy Efficiency and Renewable Energy (EERE) website6. Hydrogen has increased flammability relative to other fuels, meaning that it combusts over a wider range of fuel air mixtures. The advantage to this is that the engine can run leaner (decreases fuel/air compared to ideal stoichiometric ratio). Leaner mixtures yield more complete combustion since there is both a decreased fuel volume to combust in a given time and increased surface area to complete the reaction. Another advantage to lean operation is decreased emissions resulting from lower final combustion temperatures, which helps mitigate the production of nitrogen oxides. Since more oxygen is available, unburned hydrocarbons and carbon monoxide emissions logically decrease as well. Ignition energy is defined as the energy needed to ignite a fuel. Hydrogen has an ignition energy value an order of magnitude less than that of gasoline. This is another factor that allows leaner mixtures. However, it also means that hydrogen may ignite from “hot spots” on cylinders, resulting in precombustion, potentially causing engine damage. Hydrogen flames travel closer to the cylinder walls. The College of the Desert report calls this property decreased quenching distance, meaning it is more difficult to quench a hydrogen flame. One issue to manage as a result of this is engine backfiring on account of a partially closed valve. 2 www.savefuel.ca 3 www.hybridwaterpower.com 4 http://alternativegassolutions.com 5 www.watertogas.com 6 www.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm03r0.pdf 3 Hydrogen has a higher autoignition temperature. This feature is defined as the temperature at which the fuel/air mixture is ignited. It limits the compression ratio since the mixture heats up during compression. The compression ratio 2 1 V V is related to autoignition temperature T2 by the following equation: 1 2 1 2 1 V V T T Equation 1: Temperature compression ratio relation T1 is defined as the absolute initial temperature is the ratio of the specific heats From this equation it can be seen that higher autoignition temperature allows higher compression ratios. According to the formula for theoretical thermal efficiency, efficiency increases with compression ratio for both the Otto (petrol) and the Diesel Cycles. For the Diesel cycle, the term V3/V2 represents the volume ratio for the stage of constant pressure heat addition at the beginning of the power stroke. 1 2 1 1 1 V V th Equation 2: Thermal efficiency for Otto Cycle 1 1 1 1 2 3 2 3 1 2 1 V V V V V V th Equation 3: Thermal Efficiency for Diesel Cycle7 The ratio of specific heats for hydrogen is 1.4 and 1.1 for gasoline, indicating that thermal efficiency should be higher using hydrogen fuel instead of gasoline. This is due to the simpler structure of the hydrogen molecule, which makes the combustion reaction more 7 Moran, MJ, Shapiro, HN 4 efficient. One drawback to the higher autoignition temperature is that hydrogen is more difficult to ignite in compression ignition engines because higher temperatures are required. The flame speed of hydrogen at stoichiometric ratios is almost ten times that of gasoline. This allows a closer match to the theoretical thermal efficiency since there are decreased losses to the surroundings. The diffusivity, or the ability of hydrogen to disperse in air is higher than other fuels. This facilitates formation of a uniform fuel air mixture to give more surface area for the combustion reaction to occur and more even expansion. Furthermore, hydrogen disperses rapidly in the event of a leak, decreasing danger to users. Another design issue with hydrogen use is its low density, meaning a large volume is required for a competitive range compared to other fuels. The energy density of the fuel air mixture is lower as well since the cylinder volume is restricted. In addition, the oxygen produced by the electrolyzer and sent to the air intake of the engine may increase fuel efficiency as well. Using pure oxygen instead of air increases the actual combustion products, while reducing the amount of nitrogen in the combustion chamber. Increased nitrogen has a detrimental effect on fuel efficiency and emissions, so is not desired in the combustion intake. Oxygen enriched fuel mixtures tend to burn hotter and faster than standard air mixtures8, enhancing the effects of hydrogen. It has been noted that industrial process (steel, aluminum, glass manufacture) fuel efficiency improvements can amount to 30-60%8 by retrofitting air/fuel to oxygen/fuel combustion. The addition of significant quantities of oxygen to the combustion chamber can dramatically increase temperatures. Using small quantities oxygen as a supplement avoids this issue, while potentially yielding some benefits. Supplemental hydrogen seeks to utilize the advantages of the fuel while minimizing the drawbacks. Due to the increased flammability, ignition energy, flame speed, and diffusivity of hydrogen, it may be possible to decrease overall fuel consumption when used in a gasoline or diesel engine since leaner mixtures can be used and the cycle experiences fewer losses. At the same time, few engine modifications are required, and only water and excess alternator electricity is needed to provide the hydrogen, resulting in a relatively low cost fuel. Factors such 8 Baukal, Charles E 5 as higher ignition temperature cannot be fully utilized to increase fuel efficiency since extensive engine modifications would be required to change the compression ratio. Equipment Description The main equipment used in this investigation was the diesel fuelled electrical generator and the electrolytic cell. The electrolytic cell separates hydrogen from oxygen in the water molecule. This mixture of hydrogen and oxygen is then sent to the air intake of the diesel generator. Diesel Generator The diesel generator was an Amico model AH4000LE, rated power 4000W. A summary of the main technical specifications are shown in the following table. Rated Frequency 60 Hz Revolution speed 3600 rpm Type Single cylinder, vertical, air-cooled Bore x stroke (mm) 78 x 64 Displacement 305 cc Table 1: Generator Technical Specifications The modifications made to the generator to facilitate the test included removal of the fuel tank (for weight measurement), and removal of protective coverings for fuel line routing. A fuel tank cradle was constructed to position the fuel tank close to the engine while enabling the weight of the fuel to be measured. At the same time, this set up mitigated temperature and vibration interference. Hydrogen/oxygen Electrolytic cell (Hydrogen Generator) The hydrogen generator was a commercially available unit sold through www.savefuel.ca. Its rated output is .33 L/min at 7-8 Amps current draw, rated for use in 2L, 4 cylinder gasoline engines. The apparatus is equipped with a flashback arrestor between the electrolytic cell and the output (air intake) to prevent ignition sources reaching the cell. The flashback arrestor is simply a container which forces the gas to bubble up through water before 6 exiting to be used in an engine. The actual hydrogen generator consists of two stainless steel threaded electrodes, on which are connected thin plates separated by approximately 0.25 in. The unit is shown pictorially in Figure 1. Figure 1: H2/02 generator section cut This electrolysis method of hydrogen/oxygen production was chosen primarily for its low cost and simple operation, but it is also safer than other forms of hydrogen supply. The H2/02 generator does not store any flammable gas. All gas is sent directly to the air intake of the engine. Purchasing hydrogen in cylinders was an option as well, however, due to safety concerns and handling equipment required, it was not considered. Commercial laboratory quality electrolyzers proved cost prohibitive9. Furthermore, this style H2/02 generator is ubiquitous in any search for fuel efficiency improvement products. The gas is produced at atmospheric pressure and is drawn in by the vaccum in the air intake of the engine. This installation method is suggested by the manufacturer for automobile applications. 9 www.hgenerators.com Electrolyte level Electrodes H2/02 gas exit 7 Power Supply A power supply was needed to convert the household AC to DC for use by the electrolyzer. The power supply used for the electrolyzer in this experiment was a HYelec HY3020E. The current could be controlled from 0-10A, voltage 0-30V. However, the current and voltage were limited by the internal resistance of the electrolyzer. Measuring Instruments The equipment used to take measurements such as weight, time, and current were standard hardware store devices such that the experiment could be most economical. Loads The loads used in this experiment are standard forced air convection heaters each with a high and low setting. In addition, an array of lights was constructed for smaller load increments. Primary Experimental Procedure The following procedure was used to determine the fuel consumption of the diesel generator with and without the H2/02 injection. It was alternated 10 minutes at a time under the same load and atmospheric conditions to mitigate variations with temperature and provide quicker comparisons. Purpose The purpose of this investigation was to determine fuel consumption for the diesel electrical generator at a variety of loads. Equipment Timer/Stopwatch Diesel fuel Diesel generator Load measurement (ammeter) Dump loads (heaters) Scale Diesel generator Container (for fuel) Fire extinguisher Thermometer DC power supply 8 Set up Figure 2: Generator/weight measurement set up 1. Load measurement device connected to genset and load 2. DC power supply connected to electrodes on electrolyzer 3. Scale placed on platform 4. Fuel container filled to safe level 5. Fuel container placed on scale Procedure 1. Generator started per manufacturer’s instructions. Load connected only after exhaust gas temperature leveled off (approximately five minutes). 2. Fuel and tank weight measured together (enter Weight before) 3. Power supply turned on for proper measurement of fuel consumption with H2/02 injection, lit LED indicating proper operation. 4. Connected load 1 and run 2 minutes (if measuring no load fuel consumption omit this step) 9 5. Zeroed scale to measure fuel consumed in approximately 10 minute span by weighing fuel and tank together (enter Weight after) 6. Connected load 2 and repeated step 3 7. Readings taken as required to fill in the following table 8. Checked exhaust gas temperature over range of loads to determine abnormal operation Load 1 (A) Load 2 (A) Time elapsed (min:s) Weight before (g) Weight after (g) Analysis From the values in the above table the specific fuel consumption (sfc) was calculated in g/kWe. These values were used as fuel consumption for this generator. Sources of Error Current measurement ±0.1A (multiplied by two for two loads connected load > 13.5A) Weight ±1g Time ±1s Human factors Calculated nominal sources of error (example assuming 10 minute elapsed time): 100% min min 3600 .1 120 1 1 % No al calculated No al calculated hr s Measured current A V Measured time s Measured weight g Errorsfc Equation 3: Percent error for measurements A sample of test values was taken and the percent error resulting from the equipment ranged between and 1.60%-2.22%. Human factors are more difficult to quantify but include the manual timing and weight measurement, rather than an automatic control system. 10 Early Findings The engine/generator was found to react slowly and inconsistently with variability of the load. Thus, in the interest of reasonable results with the economical use of fuel, a secondary procedure was developed whereby the load remained constant and the H2/02 input varied. Secondary Experimental Procedure It was determined from the early findings that an optimized amount of gas would be useful to find for a variety of loads. Purpose To determine the optimum amount of H2/02 gas to use for a variety of loads Equipment Same as Primary Experimental Procedure Set up Same as Primary Experimental Procedure Procedure 1. Generator started per manufacturer’s instructions. Load connected only after exhaust gas temperature leveled off (or five minutes). 2. Fuel and tank weight measured together (entered Weight before). 3. Connected load 1 and run 2 minutes (if measuring no load fuel consumption this step omitted). 4. Power supply (10W) turned on for measurement of fuel consumption with H2/02 injection Lit LED checked to ensure operation. 5. Zeroed scale to measure fuel consumed in approximately 10 minute span by weighing fuel and tank together (entered Weight after). 6. Recorded readings as required to fill in the following table). 7. Increased DC power by 10W. 11 8. Repeated step 3-8 up to 50W DC power (omitted 4). 9. Connected load 2 and repeated step 3. 10. Checked exhaust gas temperature over range of loads to determine abnormal operation. Power to Electrolyzer (W) Load 1 (A) Load 2 (A) Time elapsed (Min:s) Weight before (g) Weight after (g) Analysis From the values in the above table the specific fuel consumption (sfc) trends were determined for a set electrolyzer power to find the optimum H2/02 gas for the load supplied by the genset. Results Early results were plagued by inaccuracies brought upon by equipment and human factors. Wherever economically viable, the instruments were upgraded to reduce these errors. This included a new scale which did not shut off automatically, thereby reducing the human impact on the results since it no longer was necessary to remove and replace the fuel tank on the scale. Also, the ammeter was replaced as it became inoperative during test. The test setup was altered since it was found that even small increases in the scale temperature produced very large distortions in the weight measurements. Where results formed a repeatable pattern, they are presented in this report. In some cases, the results were inconclusive, even erratic. The reason for this may be due to the operation of the engine during the initial 20 hour break-in period. During this period, engine components, and to a lesser extent, electrical generator equipment wears to standard operational level. For example, bearings and cylinder walls become smoother as imperfections in material and/or manufacturing are evened out with friction between parts. The final results presented are from the testing of the genset which occurred after the 20 hour break in period. They are used since they are generally more conservative and the temperature interference has been eliminated. 12 Data are presented in percent fuel savings versus electrolyzer power to determine the optimal electrolyzer input for maximum gain. The percent fuel savings is calculated relative to the baseline (no H2/02 injection) case using SFC. In equation form as follows: % 2 2 100% / Baseline Baseline H O Injection SFC SFC SFC fuel savings Equation 4: Calculation of percent fuel savings Another interesting concept to determine was the “Process Efficiency”. The process efficiency for the purposes of this investigation is defined as the ratio of the energy input to the electrolyzer to the energy offset by H2/02 injection. It was assumed that the energy content of the diesel fuel was 38.6 MJ/L and the density was 846 g/L10 . The energy flows were related by the following equations: used saved used DC saved Baseline H O Injection AC E E ocess efficiency E P t MJ Wh g L L MJ E SFC SFC P t Pr 3.6 1000 846 38.6 2 2 / Equation 5: Process Efficiency calculations In fact, the Process Efficiency plot for a 20A load case showed a profound reduction in fuel consumption compared to the energy input to the electrolyzer as shown in Figure 3. This led to an investigation to determine the source of the interference. The value of almost 700% process efficiency was deemed over expected limits. It was found that a 20-25°C increase in the scale temperature resulted in an error of more than 40% in the weight measured. This was found by measuring baseline fuel consumption at the beginning and the end of the test. These values are shown in Table 2. 10 PEC522 Notes-Energy 2000 – National Energy Policy Paper. DPIE, 1988 13 DC Power W % fuel savings Process efficiency (%) 0 (beginning) 0 0 0 (end) 44.28 Undefined 9.72 43.69 694.64 20.24 42.01 320.76 30 46.63 240.78 40.15 41.00 158.20 49.61 34.34 107.24 Table 2: Values derived from 20 Amp load test (includes temperature interference) Process Efficiency at 26 Amp Load 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 0 10 20 30 40 50 60 Electrolyzer Power (W) Ef iciency Figure 3: Process Efficiency at 20 Amp Load with Temperature interference 14 Optimization Phase During the optimization phase, it was noted that generally the H2/02 injection had a positive effect on fuel efficiency at low loads while gradually decreasing to a negative effect at high loads. Unfortunately, load cases were limited to 10A, 14A, 20A, 23A, due to the limited dump loads and time restrictions. In all, five hours out of a total 35 hours of test data was deemed valid, after discounting temperature interference, instrument failures, and process modifications. At the 35 hour point the engine began operating too erratically and often failing to operate at all such that no valid data could be derived from it. Unfortunately there was insufficient time for troubleshooting and repair, so testing was halted. 10 Ampere Load Percent fuel efficiency improvement vs electrolyzer power (~10A AC load) 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 0 10 20 30 40 50 60 Electrolyzer power (W) % fuel of set Run 1 Run 2 Figure 4: 10 Amp Load - Optimization As seen from Figure 4 (Run 2), the point where the fuel is offset most significantly is at approximately 10 WDC. At that point 18.79% of the diesel fuel is offset by the addition of supplemental H2/02. It is also important to note the large variability from Run 1 to Run 2. Since runs were performed on different days, atmospheric conditions may have produced this discrepancy. Run 1 and 2 both showed positive results. Higher air fuel ratios mean that the 15 combustion temperatures are lower (shown by decreased exhaust gas temperature of around 100°C from high to low load), as a result, the combustion may not be complete. This fact is evidenced by the greater specific fuel consumption of the engine under low load conditions. The baseline SFC is presented for reference in Figure 12. The increased efficiency may be because the H2/02 increased the flame speed and decreased the ignition temperature of the mixture for more complete combustion. Process Efficiency at 10A Load 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 0 10 20 30 40 50 60 Electrolyzer power (W) Ef iciency (%) Run 1 Run 2 Figure 5: Process Efficiency at 10A Load From Figure 5 it can be seen that the optimal process efficiency peaks above 100%. This is an important design consideration since at those conditions, it actually increased overall efficiency to have a diesel genset running an electrolyzer to inject H2/02 back into the engine. At values less than 100%, yet still greater than 0%, it may only be logical to use an electrolyzer as a dump load. The leveling out of the efficiency curve shows that added H2/02 still provided some benefit, but with diminishing returns on input energy. 16 14 Ampere Load Percent fuel efficiency improvement vs electrolyzer power (~14A AC load) -2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00 0 10 20 30 40 50 60 70 Electrolyzer power (W) % fuel of set Run 1 Run 2 Figure 6: 14 Amp load – Optimization It can be seen from Figure 6 that the values were very close to the range of sources of error (1.60-2.22%), but there are some interesting points. The peak efficiency occurs when the electrolyzer is set to 30 W DC. This may be as a result of the greater amount of fuel that wasinvolved in the combustion reaction, making it more complex and slower. Thus more H2/02 was needed to provide any benefit such as increasing flame speed. One important trend, when compared to Figure 4, to note is that the relationship between fuel consumption and optimal H2/02 injection is not linear. That is, for an increase in fuel consumption of 13% the optimal electrolyzer power required increases 300% or more. It could be that the actual optimum requires increasing electrolyzer power even further as shown by the upward trend of Run 1. The process efficiency curve (Figure 7), as expected, complements Figure 6, but it is important to note that the curve never rises over 8%. As a result, with the equipment in this investigation, the electrolyzer would only be operated as a dump load. However, if low H2/02 inputs were avoided, efficiency improvements are possible. 17 Process Efficiency at 14A Load -1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 0 10 20 30 40 50 60 70 Electrolyzer power (W) Ef iciency (%) Run 1 Run 2 Figure 7: Process Efficiency at 14A Load 20 Ampere Load The following plot at the 20 A load condition shows general efficiency improvements over the baseline case but shows some indication that the optimum H2/02 output may be beyond the capability of the power supply circuit. The reason for this suspicion is the non linear relationship between H2/02 output and fuel consumption as shown in the 14 A load case and the pattern of both 10 A and 14 A load case, stable efficiency except for the relatively pronounced optimum point, which is missing in Figure 8. The optimum process efficiency plot from Figure 9 emphasizes the steady results shown in Figure 8. Since the same efficiency (within 1.5%) improvement was found over the range of electrolyzer power tested the maximum process efficiency occurs at the lowest input power (10 W). 18 Percent fuel efficiency improvement vs electrolyzer power (~20A AC load) 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 0 10 20 30 40 50 60 Electrolyzer power (W) % fuel of set Figure 8: 20 Amp load – Optimization Process Efficiency at 20A Load 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 0 10 20 30 40 50 60 Electrolyzer power (W) Ef iciency (%) Figure 9: Process Efficiency at 20 A Load 19 23 Ampere Load The largest load tested (23 A) proved to be the breaking point in efficiency improvements. It was noted that efficiency improvements were not realized. While the decreases in efficiency noted were not large, it is important to avoid operating a system in this mode for extended periods. However, it can also be noted that the curve begins an upward trend at higher electrolyzer power that might reveal a positive optimum point with a higher DC power supply capacity. If time allowed, it would be interesting to explore this by modifying the circuit to increase amperage to the electrolyzer. It was decided not to present the process efficiency plot as it was entirely negative. Percent fuel efficiency improvement vs electrolyzer power (~23A AC load) -6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00 0 10 20 30 40 50 60 70 Electrolyzer power (W) % fuel of set Figure 10: 23 Amp load – Optimization It was originally thought that the reason for the rise in fuel consumption was due to the decreased air fuel ratio at high loads. The air fuel ratio is defined as the proportion of the mass of air to the mass of fuel used in the combustion reaction. As the amount of fuel injected into the cylinder is increased, it requires a greater amount of air for complete combustion. Since hydrogen is much less dense than air, it may have displaced the combustion air thus leaning 20 the air/fuel mixture. The H2/02 gas may have recombined to form water and was thus not used for combustion of the fuel. More fuel would be automatically injected to compensate for the lean mixture while still meeting the load. For a diesel engine, the air/fuel ratio is variable with loading, atmospheric conditions, and engine design. The following assumptions were made to approximate the air fuel ratio for the Amico diesel engine used in this experiment. Each intake stroke is restricted to the rated displacement of the engine (305 cc) Constant speed of 3600 rpm (from manufacturer’s specifications) Density of air 1.225 kg/m3 (standard Temperature and pressure at sea level) min 336.26 1 1000 1.225 1 10 1 min 3600 4 305 6 3 3 3 3 g kg g m kg x cm rev m rev cm Equation 6: Air usage of Amico engine Load vs Air/fuel ratio 0 5 10 15 20 25 30 35 40 0 500 1000 1500 2000 2500 3000 Load (W) Air/Fuel Ratio Figure 11: Approximation of air fuel ratio for Amico engine It can be seen from Figure 11 that air fuel ratio increased with load from approximately 34:1 at 10 A load to 22:1 at 23 A load. The volume of air displaced by H2/02 was calculated using the following procedure: 21 The power supply was set to maximum (9.4A, 5.7V) and connected to the electrolyzer for 2.534 hours. The weight of water converted to H2/02 gas was 13 grams. The volume of hydrogen was calculated using the following method: Known: Hydrogen=0.090 g/L Oxygen=1.429 g/L 2 2 2 2H O 2H O Equation 7: Electrolysis reagents 2 mole H2O =36 g 2 mole H2=4 g=MMH2 1 mole O2=32g=MMO2 Assumed gases exist as diatomic molecules hr L v hr m L v hr g m hr g m hr g hr g m MM MM m m O H H H O H H O O H H H O 3.141 7.134 5.130 0.641 4.489 0.641 5.13 2.534 13 2 2 2 2 2 2 2 2 2 2 2 Equation 8: Calculation of volumetric flows of electrolyzer This indicates that the H2/02 was displacing 10.275 L/hr of combustion air. Since the engine consumes about 275 L/min of combustion air, it can be assumed that the supplemental H2/02 has a negligible effect due to volume displacement. There are no external signs of precombustion at the higher loads, but exhaust gas temperatures are certainly higher (160°C at idle, 300°C at high loads) so that may contribute somewhat to the decreased 22 efficiency. Precombustion may occur when the H2/02 mixture experiences a sufficient temperature increase to combust. Since the mixture has a low autoignition temperature, it may burn when injected to a hotter cylinder before the fuel is even injected. As a result of the uncertainty surrounding the operation at high loads with H2/02 injection, more research is needed. Discussion Significance of Results Any neutral party results from testing these H2/02 generators are significant since there is very little verified evidence available. In fact, during the course of this experiment a single report was found originating from a third party15, unfortunately only the abstract was available. The bulk of information available remains on manufacturers’ or “tinkerers’” websites and can be discounted as claims and lacking detail for proper system integration (eg. process efficiency). Despite the challenges of working with a small engine to produce reliable results, there was some evidence derived from this experiment to support the use of supplemental H2/02 injection to reduce fuel consumption in some cases. For comparison, Umpqua Energy, an Oregon company uses the same principle for its H2/02 generators, stating expected fuel savings to be in the 3-12% in transport applications11. Canadian Hydrogen Eenergy Company guarantees a 10% savings12. Assuming a 10% increase in fuel economy for diesel applications, the resulting fuel savings would amount to 451800 barrels of diesel fuel per day in the United States alone (based on EIA consumption estimates for diesel fuel)13. Also, the technology has the potential to decrease emissions based on Umpqua Energy claims as shown in Table 3: Emission Percent Reduction NOx Up to 60 Carbon Monoxide Up to 100 Hydrocarbons Up to 100 Particulates Up to 95 11 www.umpquaenergy.com 12 www.chechfi.ca 13 http://tonto.eia.doe.gov/dnav/pet/pet_sum_sndw_dcns_nws_w.htm (Energy Information Administration) 23 Opacity (Smoke) Up to 70 Table 3: Claimed emission reductions with H2/02 injection11 Thus the addition of H2/02 gas has the potential to provide additional benefits even if efficiency gains are marginal. The significance of this is that it eliminates a potential drawback of H2/02 injection such that the device may be used in additional applications for its additional benefits rather than simply where commercially logical. Another significant finding was the pronounced improvement in diesel efficiency at low load factors with H2/02 injection. Load factor is the proportion of the rated load of the generator (4kW) in this case. Increasing fuel economy in the low load regime makes the technology more applicable in wind diesel grids. For example, the Denham wind diesel grid14 incorporated low load diesels to support the grid frequency while wind energy is high since it is too variable to provide the expected power quality. At the same time, the diesel generator is able to follow the load. If operated at low load in an efficient manner, a larger proportion of electricity is available for spinning reserve without bringing an additional generator online. The low load diesels were specially designed such that maintenance problems arising from operation at low load were mitigated, with added cost. In theory, with supplemental H2/02 injection the improved combustion characteristics and increased efficiency may make it possible to use a standard diesel to accomplish the same task. The following plot derived from the results of this experiment show the potential effectiveness of H2/02 injection at lower loads, it can be noted by the expanding gap between the baseline and H2/02 injected SFC values below 30% rated capacity. 14 PEC520: Case Studies of Renewable Energy Systems notes or http://www.verveenergy.com.au/mainContent/sustainableEnergy/OurPortfolio/Denham_Wind _Farm.html 24 Load vs SFC 0 0.1 0.2 0.3 0.4 0.5 0.6 0 500 1000 1500 2000 2500 3000 Load (W) SFC (kg/kWh) Baseline Min with H2/02 inj Linear (Baseline) Linear (Min with H2/02 inj) Figure 12: Comparison of Baseline and Minimum H2/02 injected SFC An additional factor in the adoption of supplemental H2/02, as in the Denham case, could be the elimination of dump loads such as boilers while maintaining the wind penetration level. The boiler could be replaced by an electrolyzer so that during periods of high winds, hydrogen fuel is created from the excess energy. Although, additional cost and safety issues arise when hydrogen and oxygen are separated and stored. There would exist the opportunity to use the hydrogen for transport, as in fuel cells, or other uses where economically viable. According to Levene, J. Kroposki, B. Sverdrup, G, hydrogen produced by wind energy can be cost competitive with petroleum fuel. Hydrogen produced at point of use is currently estimated to be $5.55US/kg (2006 figures) in the short term and $2.27US/kg in the long term. One kilogram of hydrogen is about equivalent in energy to 1 gallon of gasoline (currently $3.29US/gal in the Seattle area). The advantages of supplemental hydrogen injection could be extended to small SAPS (Stand Alone Power Supplies) incorporating wind turbines and diesel generators. The components of the supplemental H2/02 electrolyzer are inexpensive and simple enough that one can be custom made for any application. The electrolyzer uses DC, traditionally output from wind turbines directly, thus avoiding power losses and cost of additional power 25 conditioning equipment. The opportunity to increase wind penetration in wind diesel with H2/02 injection shows some promise, but further investigation is required. Limitations Unfortunately, very little published data exists to support or refute the findings from this investigation. One such report supporting the findings in this experiment, a PhD thesis from the University of Tasmania, did find that: “The research particularly established that vitiation and enrichment effectiveness was only realised at low rather than high loads indicating that hydrogen achieved more than diesel mass substitutions”15 This statement does support the evidence found in this investigation; however, this was using an indirect injection engine with pure hydrogen, and quantitative results were unavailable. As a result of the limited amount of complementary data, the scope is limited to this engine and H2/02 electrolyzer under the prevailing conditions in the location tested. There are claims of 10% fuel efficiency11,12 increases with the same technology in comparable situations. Further research is required to verify the effects of H2/02 injection in a variety of conditions for other sizes and types of internal combustion engines for the technology to become more widely adopted. As noted in the results, the technology may end up being limited to transport or other (eg. off-grid) applications where the electricity used for the electrolyzer would otherwise be wasted. Achievements Despite the many frustrations experienced over the course of this experiment, overall, it was beneficial. Many previous assumptions were displaced with first hand knowledge. For example, originally exhaust gas temperatures were assumed to be relatively constant, and higher. It was found that the temperature varied by 140°C. Through problem solving and testing, hands-on knowledge of electrical generating equipment, test instrumentation, process improvement and diesel engines was gained. Through theoretical research, more was learned about the diesel cycle, particularly in comparison to the Otto cycle. In addition, some positive 15 Hafez, HA 26 fuel efficiency improvements were found under certain load conditions. Particularly, the results here were found to merit investigation for the potential application in wind diesel grids. Another important achievement of this experiment is in expanding the body of knowledge on the subject of H2/02 supplementation. In sum, many of the learning objectives of the experiment were achieved even though hydrogen injection may not be the panacea for fuel efficiency under all conditions. Conclusion The injection of H2/02 gases into the diesel in this investigation did show some promise of fuel efficiency improvement. It was found that savings of over 18% were possible with this technology, at low load conditions, in the situation tested. However, as the load increased, the savings were reduced, and gradually, the fuel consumption actually increased with H2/02 injection. Consequently, the system incorporating H2/02 must be carefully designed to discontinue injection before it causes detrimental effects. The technology does have a potential application in wind diesel grids such as Denham or small SAPS to decrease fuel consumption and increase wind penetration with integrated system control. It could readily be adapted to transport applications if the vehicle tends to be lightly loaded. Fuel efficiency improvement is an important issue since fossil fuels are a non-renewable resource. Additionally, using water to offset fossil fuels promotes energy independence, since it is a compound that can be found anywhere there are humans. The amount of water used would not risk any supply as it is extremely low consumption. While this experiment did not test emissions from the engine, Hafez, HA15 states: “Contrary to the common belief, green house gases, nitrogen oxides, hydrocarbons and opacity substances do not coincidently all increase and/or decrease. Indeed, this experiment demonstrated that although the diesel-hydrogen nitrogen monoxide (NO) wet-emissions at all injection rates were partially lower than the diesel baseline, carbon oxides, hydrocarbon emissions, opacity (N) and absorption coefficients (k) were higher. In other words, a measure taken to limit the harm done to human health can increase the damage to the environment and vice versa.” Thus, emissions control is not a significant advantage to H2/02 injection. 27 In remote, developing areas, where diesel fuel is used for many applications such as backup electrical power, water pumping for irrigation and drinking, and transportation, fuel savings could result in a higher quality of life as greater financial resources are made available for education and healthcare. The experiment succeeded in enhancing the field of knowledge in general, and for the author. In addition, it was shown that H2/02 injection into diesel engines can provide fuel savings, but more research is necessary to broader the application of this technology. Opportunities There are many opportunities for further research in the field of H2/02 injection and fuel efficiency improvement. First of all, an expansion of the scope into other internal combustion engines would be extremely useful. Unfortunately, the experiment was limited to loads above 25% of the rated capacity of the genset, yet the Denham wind diesel grid operated the gensets down to 7%. Any following research should include the load regime between 0- 25% of rated load. It would be interesting to determine the effects of hydrogen and oxygen injected separately, as there is some evidence that either may have its benefits. While more complicated, injecting pressurized hydrogen at the same time as the fuel, may have the potential for increased fuel savings over a broader load range. Pressurized oxygen is not recommended to be injected into an internal combustion engine since excess heat resulting in engine damage is probable. Lessons Learned It is possible that the most valuable portion of this experiment is the provision of lessons learned as well as some encouragement to carry on with further experiments in this field. These are presented to save the researcher who continues the study of H2/02 injection for fuel efficiency improvement as much time and money as possible. Firstly, it is recommended that a larger, higher quality engine be used, incorporating multiple cylinders, to better simulate the aggregate effects of the H2/02 injection. With the small, single cylinder engine, it is not immediately scaleable to multiple cylinder engines, due to air intake variables. Thus, an experiment using a multiple cylinder engine would be more 28 useful. The engine used in this experiment was an inexpensive model, thus it provided a source of frustration in cases when it would not operate. If a flow meter is used, it is more difficult to find one that measures the minute fuel flows consumed by the Amico. So the greater fuel consumption could supply more accurate results. Also, if possible, the engine should be only minimally modified. The test setup should be suited to the engine, not the other way around. Invariably, fuel lines will be impossible to find replacements, for example. A higher quality engine is more likely to yield consistent results. Unfortunately the Amico was unstable, as shown by the difference in Run1 and 2 in Figure 4 and Figure 5. In hindsight, a gasoline/petrol engine would have been preferred over a diesel for this experiment. They are cheaper to buy, more prolific, and currently the fuel is less expensive. An additional benefit is the provision of a DC circuit while the engine is running. This is possible with diesel engines as well, but not with the Amico model in this experiment. It is worth checking if there is a DC circuit since that would make the power supply to the electrolyzer much easier to integrate. It was learned after the purchase of the Amico about the lack of DC supply, as a result, an additional component had to be purchased to convert household AC to DC. In addition, much of the focus in the marketing of H2/02 generators is for gasoline applications. Gasoline is inherently less efficient than diesel due its lower compression ratio so it may be that higher gains are possible with spark ignition engines. The design and construction of the H2/02 generator simple and inexpensive, so it would be worthwhile to construct one custom made for the application. Ideally, this would produce a H2/02 generator with known electrical consumption versus output characteristics, suited to the engine. Likely, constructing a custom made H2/02 generator would be less expensive as well. With greater resources, it would be beneficial to incorporate more advanced sensors such as flow meters for fuel consumption and H2/02 output, temperature sensors for exhaust gas and cylinders, and an automatic test control system. The control system could vary the load and take instantaneous reactions of the engine to H2/02 input as well as averaging the data. Instantaneous measurements were impossible with the setup in this experiment, but may prove interesting. Also, a diesel engine is not a welcome neighbour for noise and toxic emissions, thus it would be advantageous to avoid manual data taking, when possible. At the 29 same time, greater precision would reduce sources of error. Wasted time due to failed instruments would be mitigated. References HydroGenX Corporation www.savefuel.ca Hydrogen Use in Internal Combustion Engines. College of the Desert. url:www.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm03r0.pdf Baukal, Charles E. Oxygen-Enhanced Combustion. CRC Press, 1998. Hafez, HA. A Study of Diesel-Hydrogen Fuel Mix in a Stationary Compression Engine. PhD thesis, University of Tasmania, 2007. Umpqua Energy www.umpquaenergy.com Canadian Hydrogen Energy Company www.chechfi.ca Energy Information Administration http://tonto.eia.doe.gov/dnav/pet/pet_sum_sndw_dcns_nws_w.htm Levene, J. Kroposki, B. Sverdrup, G. Wind Energy and Production of Hydrogen and Electricity – Opportunities for Renewable Hydrogen. National Renewable Energy Laboratory conference paper, March 2006. Cotrell, J. Pratt, W. Modeling the Feasibility of Using Fuel Cells and Hydrogen Internal Combustion Engines in Remote Renewable Energy Systems. National Renewable Energy Laboratory technical paper, September 2003. Dempsey, P. Troubleshooting and Repairing Diesel Engines, 3rd Edition. TAB Books. New York, 1995. Sandia corporation Combustion Research Facility webpage url:www.sandia.ca.gov/crf/research/combustionEngines/PFI.php - Moran, MJ, Shapiro, HN. Fundamentals of Engineering Thermodynamics. John Wiley & Sons. New York, 2000. Hunter, R. 2030: Confronting Thermageddon in our Lifetime. McClelland & Stewart. Toronto, 2003.