Quote:
Originally Posted by NeilBlanchard
This may make the engine a little more efficient, but at the thermal efficiency level -- why isn't an internal combustion engine as efficient (or even close to the same efficiency) of an electric motor? I'm talking quantum leaps here. Streamlining cranks ain't going to be enough.
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Engine efficiency is limited by the combustion temperature (hot source) and the local (cold sink) temperature. We can't do a whole lot to lower the temperature of the cold sink, so the best we can do is design materials that can take higher combustion temps and/or use fuels with high combustion temps. Heavy duty diesels tend to be more efficient than heavy duty gasoline engines because diesel has a higher temperature of combustion (This gets tossed out the window due to EGR if the engines have to meat the same emissions regs), so those tend to be the best
at ~54% for large low speed diesels that don't need to accommodate emissions regulations and are run at maximal efficiency. To get beyond that we would probably need another hotter fuel source and better materials. Electric motors aren't bound by the same efficiency constraints, and as such their efficiency is much much higher.