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The small number of vehicles using hydrogen internal combustion engines (HICE) makes it difficult to explain how to repair them. Therefore, this section does not serve as a repair manual, but as an outline describing the operation of a hydrogen engine and its major components, its benefits, drawbacks and how components can be modified or re- designed to reduce the drawbacks.

In general, getting an internal combustion engine to run on hydrogen is not difficult. Getting an internal combustion engine to run well, however, is more of a challenge. This section points out the key components and techniques required to make the difference between a hydrogen engine that just runs and one that runs well.

The earliest attempt at developing a hydrogen engine was reported by Reverend W. Cecil in 1820. Cecil presented his work before the Cambridge Philosophical Society in a paper entitled "On the Application of Hydrogen Gas to Produce Moving Power in Machinery." The engine itself operated on the vacuum principle, in which atmospheric pressure drives a piston back against a vacuum to produce power. The vac- uum is created by burning a hydrogen-air mixture, allowing it to expand and then cool. Although the engine ran satisfactorily, vacuum engines never became practical.

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