A device for converting heat into work. The heat is derived from the combustion of a fuel. In an internal-combustion engine the fuel is burnt inside the engine, whereas in a steam engine or steam turbine, examples of external-combustion engines, the fuel is used to raise steam outside the engine and then some of the steam’s internal energy is used to do work inside the engine. Engines usually work on cycles of operation, the most efficient of which would be the Carnot cycle. This cannot be realized in practice, but the Rankine cycle is approximated by some engines.