How are internal combustion engines different from external combustion engines?

External combustion engine run smoothly and silently where of internal combustion engines are very noisy. Noise produce from continuous explosions inside the cylinder of IC engine.

An external combustion engine (EC engine) is a heat engine where a working fluid, contained internally, is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work.