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

There have been proof-of-concept ICE/Steam hybrid cars that inject water to the cylinder on the fourth stroke, which then bursts into steam for another push, but they aren’t realistic for production (injecting water to your cylinders will only f••k up your engine *badly* in a short amount of time).