Yuriman
Diamond Member
- Jun 25, 2004
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It appears the chart ignores losses before the flywheel, such as thermodynamic losses in the engine. For example, for a modern gas engine with a compression ratio of 11.6, the max theoretical efficiency would be 37.5%, so 62.5% of the energy in every gallon of gas goes out the tailpipe or into the radiator.
In realty the actually efficiency is probably quite a bit lower than the theoretical max.
So while aerodynamic losses are large, more than 2/3 of the energy is lost to waste heat no matter what speed you are going.
You're right, of course. I'd like to add that some of the losses before the flywheel can be changed by things like gearing, too; for example bringing engine load up closer to 100% at a lower RPM generally increases effiency, both by increasing cylinder pressure and by reducing pumping losses, as do driving at higher altitude and increasing intake air temperature, so now that I think about it, that chart isn't all that useful.
Here's a fun one I picked up over at Ecomodder when I was doing research on gen1 Insights before buying one:
Boy do those parasitic losses grow.