An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
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All chemically fueled heat engines emit exhaust gases. The cleanest engines emit water only. Strict zero-emissions generally means zero emissions other than water and water vapour. Only heat engines which combust pu… See more

The word engine derives from Old French engin, from the Latin ingenium–the root of the word ingenious. Pre-industrial weapons of war, such as catapults, trebuchets and battering rams, were called siege engines, and knowle… See more

Simple machines, such as the club and oar (examples of the lever), are prehistoric. More complex engines using human power, animal power, water power, wind power and even steam power date back to antiquity. Human po… See more

An engine can be put into a category according to two criteria: the form of energy it accepts in order to create motion, and the type of motion it outputs.
Combustion engines are heat engines driven by the hea… See more