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).
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).
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).
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