In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work.
There are two main types of heat engines: external combustion and internal combustion:
In an external combustion engine, the fuel burns outside and away from the main bit of the engine where the force and motion are produced. ...
In an internal combustion engine, the fuel burns inside the cylinder.
Internal engines