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The majority
of true micro CHP systems are currently based on external combustion
technology as their characteristics are best suited to this stationary,
constant running application.
External
combustion engines separate the combustion process (which is the energy
input to the engine) from the working gas, which undergoes pressure
fluctuations and hence does useful work.
As the combustion process is used to
provide a continuous heat input to the working gas, it is more
controllable and generally more
efficient, cleaner and quieter than internal combustion engines.
The two most common external
combustion engines are the Stirling engine, in which a working gas is
alternately heated and cooled to create pressure changes which in turn
drive a power piston, and the Rankine engine in which a fluid is heated
to evaporate and expand against a piston or turbine, and then cooled and
condensed prior to the next heating and cooling cycle.
For further discussion of
the relative merits of engine types see section on
papers.
For information on products
under development, click on the respective
Rankine
and Stirling links below.
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