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PowerPedia:External combustion engine

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An external combustion engine (abreviation ECE) is a heat engine which burns fuel to heat a separate working fluid which then in turn performs work. Examples include steam engines and Stirling engines.

For the same power, external combustion engines are often less compact and heavier than internal combustion engines. This is because they contain a heat exchanger to heat the working fluid. However, they can be more efficient, and are much less particular about the type of fuel they burn. They also tend to be cleaner due to lower combustion temperatures and pressures which create less exotic exhaust gasses, such as nitrogen oxides (NO, NO₂ etc.).

A steam turbine is a good example of an external-combustion engine. Heat from burning fuel or from a nuclear reactor changes water in a boiler to steam. Pipes carry the steam into the turbine, which has a series of bladed wheels attached to a shaft. The high-temperature steam expands as it rushes through the turbine and so pushes on the blades and causes them to turn the shaft. Steam leaving the turbine has a much lower temperature. The spinning shaft can drive an electric generator, move a ship's propeller, or do other useful work. Externally heated cycles include the Stirling cycle, Ericsson Cycle and Brayton cycle.