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

Question

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?

In: 407

Answer 1

Ice engines use small explosions and not heat to turn the crankshaft. The excess heat is just a result of that. You can’t really use that for turning the wheels without having a separate engine that turns heat into movement.