An internal combustion engine (ICE) is a heat engine in which the combustion (burning) of a fuel occurs within the combustion chamber. ICEs are typically powered by fossil fuels like natural gas or petroleum products such as gasoline, diesel fuel or fuel oil. If burning takes place inside the engine, the pressure built up by burning the fuel is converted to mechanical work by exerting a force which pushes a piston or turns the blades of a turbine.

The fact that fuel can be burn inside the engine, unlike the steam engine, reduces the energy loss outside the engine and increases its efficiency. Gasoline engine, diesel engine and jet propulsion engine are examples of internal combustion engines.