engine

engine Machine that produces useful energy of motion from some other form of energy. The term is usually restricted to combustion engines, which burn fuel. These machines include the steam engine, diesel engine, jet engine, and rocket engine. Such engines are distinguished from electric motors which, in providing their power, do not directly alter the chemical or physical composition of a substance. Combustion engines are of two main kinds: an external combustion engine burns its fuel outside the chamber in which motion is produced. In a steam locomotive, for example, the fire box is separate from the cylinders. An internal combustion engine burns its fuel and develops motion in the same place.