eli5: why are ICE engines only able to achieve 20-30% thermal efficiency?

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I read that a massive portion of usable energy is wasted and turned to heat instead of being used to turn the crankshaft — would there be like any way of reducing the heat/cooling the engine so you could get 50-70% thermal efficiency?

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Anonymous 0 Comments

Important note, *gasoline* engines only get 20-30% efficiency diesel engines are currently pushing high-40 to low-50% thermal efficiency.

In fact, Rudolph Diesel theorized that at about 60% efficiency an external cooling system wouldn’t be needed and the Reisser cycle engine successfully proved that requiring no cooling system.

Diesel engines are far better than their gas counterparts.

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