An external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion of 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 cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).

"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; but are not then strictly classed as external combustion engines, but as external thermal engines.

The working fluid can be a gas as in a Stirling engine, or steam as in a steam engine. The fluid can be of any composition; gas is by far the most common, although even single-phase liquid is sometimes used. In the case of the steam engine, or the Organic Rankine Cycle the fluid changes phases between liquid and gas.

[edit] Research, development and innovation

A Spanish engineer has patented the design of a cold external combustion engine, which he claims can be cleaner, more powerful and with higher fuel economy than the current Internal Combustion engines. The engine has been developed by Alba Montecristo based in Daimiel (Ciudad Real, Spain) and Air Car Factories ^[2], and will be used as an external accessory to power conventional engines. The engine does not need any oil for operation, but uses a new solid-liquid fuel, which the maker claims costs much less than oil. It can also use compressed air.^[3] A fully functional prototype is expected by 2011.^[4][5]

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