The diagram
above shows a beta type stirling cycle. This engine may seem
different when looking at it, but the cycle is no different than other
types of stirling engines. Basically they run because
PV = NRT
In other words, air expands as it is heated and contracts as it is
cooled (kinetic theory of gasses).
By alternating between heating and cooling, the work done by the power
piston can be converted to mechanical energy.
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As you can see in the
above photo, the displacer piston runs 90 degrees out of phase with the
power piston. This is what allows the engine to run. In the PV diagram
below, points 1 through 4 correlate to the pictures labeled 1 through 4
above, showing how the cycle works visually.
Some Stirling engines have efficiencies close to that of the
carnot cycle (shown in the lower left), which is the maximum efficiency
that a heat engine can reach. Notice that AB and CD are iso-therms and
BC and DA are adiabats. The sterling engine cannot do this in reality,
but can come close compared to other heat engines.
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