Posted by Sherman in Idaho [72.47.153.61] on Sunday, February 22, 2015 at 17:33:16 :
In Reply to: Re: I don't believe it. posted by Kaegi [76.22.23.236] on Saturday, February 21, 2015 at 16:12:33 :
Only about 1/4 of the energy in the gasoline turns into HP at the wheels. In a good small internal combustion engine, 1/3 of the energy tuns into flywheel HP. But that's about thermodynamic efficiency of the Otto cycle with currently-available materials, not about combustion efficiency.
These days, the fuel is very close to 100% burned. If 27% was going out the exhaust pipe unburned, you could set the exhaust on fire. That's obviously bogus. The inefficiency is in the percentage of energy from the (perfectly) burned fuel that turns into shaft horsepower. 2/3 of it is lost as waste heat.
The inefficiency is in the thermodynamic cycle, which is a function of source (combustion) temperature and sink (ambient) temperature. That's where all the remaining gains can be gotten (running the engine hotter, basically).
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