Abstract:Hydrogen can be used in one of two ways for transportation, in a conventional combustion engine or in an electrochemical fuel cell. Hydrogen used in a combustion engine is similar to using natural gas. It is inducted into the engine, combusted and the byproducts exhausted. The predominant exhaust components are vaporized water and nitrogen. Small amounts of carbon dioxide, carbon monoxide and hydrocarbons result from engine lubricating oil. Depending on the operating conditions (engine stoichiometry and operating pressure) nitrogen oxides are also formed. In general, hydrogen is the cleanest possible fuel for any combustion engine. The electrochemical fuel cell converts hydrogen energy directly to electrical energy in the reverse reaction of water electrolysis. The electrical energy is used to operate an electric propulsion system. The exhaust from the fuel cell is predominately vaporized water, nitrogen and unused oxygen. No nitrogen oxides are formed and conversion efficiency varies depending on electrical load from 70 to 45%. The fundamental difference between the two options for using hydrogen is that the fuel cell is substantially more efficient (approximately a factor of two, depending on driving cycle characteristics) and there are no regulated exhaust emissions. These advantages result in a lower fuel usage, smaller on-board storage system and a qualification as a zero emission vehicle power system. However, the heat engine is highly developed while fuel cells are very much in a development stage. The ultimate cost and performance of fuel cells are unknown. In comparison to battery powered vehicles, hydrogen provides an opportunity to have clean, sustainable energy based transportation with rapid refueling as well as long ranges of conventional fuels.

The following four subsections deal with the technical aspects of using hydrogen as a transportation fuel. The first subsection describes the intrinsic properties of hydrogen and it is compared on a safety basis to natural gas and gasoline. The second subsection describes production, distribution and storage issues. The third subsection details possible refueling scenarios and hardware needs. The fourth subsection compares hydrogen to natural gas and batteries as a transportation fuel. The fuels are compared on a performance, emission and refueling basis. Finally, a summary of these findings is given.

Note:Prepared for the California Energy Commission as part of the 1994 California Fuels Project.