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An external combustion engine (EC engine) is a reciprocating heat engine where a working fluid, contained internally, is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work.[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
[edit]"Combustion" refers to burning fuel with an oxidizer, 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.
Working fluid
[edit]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).
Single phase
[edit]Gas is used in a Stirling engine. Single-phase liquid may sometimes be used.[clarification needed]
Dual phase
[edit]Dual-phase external combustion engines use a phase transition to convert temperature to usable work, for example from liquid to (generally much larger) gas. This type of engine follows variants of the Rankine cycle. Steam engines are a common example of dual-phase engines. Another example is engines that use the Organic Rankine cycle.
See also
[edit]- Organic Rankine cycle
- Steam engines
- Stirling engines
- Trochilic engine
- Internal combustion engine (ICE)
- Nuclear power
- Solar thermal rocket (an externally heated rocket)
- Naptha engine, a variant of the steam engine, using a petroleum liquid as both fuel and working fluid.