Engine Efficiency

The efficiency of various types of internal combustion engines varies, but it is nearly always lower than 1 electric motor energy efficiency. Most gasoline-fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20% [1][2]. The efficiency may be as high as 37% at the optimum operating point. Most internal combustion engines waste about 36% of the energy in gasoline as heat lost to the cooling system and another 38% through the exhaust. The rest, about 6%, is lost to friction. Rocket engines can approach 70% efficiency at some parts of a flight; made possible by the very high combustion temperature and lower exhaust temperatures, but while the average efficiency depends on the mission, for a launch vehicle to reach Low Earth Orbit the overall efficiency is only around 10%.

Hydrogen Fuel Injection, or HFI, is an engine add-on system that improves the fuel economy of internal combustion engines by injecting hydrogen as a combustion enhancement into the intake manifold. Fuel economy gains of 15% to 50% have been claimed [citation needed]. A small amount of hydrogen added to the intake air-fuel charge increases the octane rating of the combined fuel charge and enhances the flame velocity, thus permitting the engine to operate with more advanced ignition timing, a higher compression ratio, and a leaner air-to-fuel mixture than otherwise possible [[2]]. The result is lower pollution with more power and increased efficiency. Some HFI systems use an on board electrolyzer to generate the small amount of hydrogen needed in the system, around 5% of total BTU. A small tank of pressurized hydrogen can also be used, but this method necessitates refilling. Hydrogen in liquid form is seldom used because it is difficult to store.

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