Engine-Efficiency

The efficiency of various types of internal combustion engines vary. Most gasoline fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20% . The efficiency may be as high as 37% at the optimum operating point in engines where this is a high priority such as that of the Prius. 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. But this technology is one of the leading factors to global warming and pollution.
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% can be seen[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. The result is lower pollution with more power and increased efficiency. Some HFI systems use an on board electrolyzer to generate the hydrogen used but this appears to have little credibility at this time given the small amounts of gas produced from them. A small tank of pressurized hydrogen can also be used, but this method necessitates refilling and Hydrogen in liquid form is difficult to store in any usable volume.
There has also been discussion of new types of internal combustion engines, such as the Scuderi Split Cycle Engine, that utilize high compression pressures in excess of 2000 psi and combust after top-dead-center (the highest & most compressed point in an internal combustion piston stroke). The claimed efficiency of this engine, by calculation, is 42%. This has yet to be demonstrated as of March 2007.