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

There are a lot of losses. You hear the engine? That’s energy being lost. Every moving component has friction. You need energy to overcome that friction.

The exhaust gasses are hot, which is also energy being lost through the exhaust.

These losses are before you even consider the large amount of heat put into the cooling system, which is lost to the environment through the radiator.

You can harness this energy in a similar way to how your car heating system works using stationary engines. The cooling system carries heat to the heater matrix and a fan blows air through it to heat your cabin. This same principle is used in combined heat and power gensets where they use the heat energy to feed radiators or hot water systems.

In this application, the engine is used to drive an alternator to supply a building with electricity. Usually, the engine just gets rid of this heat through the exhaust and radiator, however in a CHP they use a jacket around the exhaust and sometimes through the cooling system. They pass the heat into water, and it’s fed into a building using a heat exchanger.

Efficiencies here can be in the high 80s or more, especially if used for cooling too.

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