| Part of a series on |
| Aircraft propulsion |
|---|
| Shaft engines: drivingpropellers,rotors,ducted fans orpropfans |
| Reaction engines |
Anexternal combustion engine (EC engine) is areciprocatingheat engine where aworking fluid, contained internally, is heated by combustion in an external source, through theengine wall or aheat exchanger. The fluid then, by expanding and acting on themechanism of the engine, produces motion and usablework.[1] The fluid is then dumped (open cycle), or cooled, compressed and reused (closed cycle). In these types of engines, the combustion is primarily used as a heat source, and the engine can work equally well with other types of heat sources.
"Combustion" refers toburningfuel with anoxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; they are not then strictly classed as external combustion engines, but as external thermal engines.
The working fluid can be of any composition and the system may be single-phase (liquid only or gas only) or dual-phase (liquid/gas).
Gas is used in aStirling engine. Single-phaseliquid may sometimes be used.[clarification needed]
Dual-phase external combustion engines use aphase transition to convert temperature to usable work, for example from liquid to (generally much larger) gas. This type of engine follows variants of theRankine cycle.Steam engines are a common example of dual-phase engines. Another example is engines that use theOrganic Rankine cycle.