How Stirling Engines Work
The Alpha (Two-Piston) Stirling
The two pistons in the animation
accomplish all of the stages of the Stirling Engine's cycle.
Heat applied to the gas inside the heated cylinder causes pressure
to build. The pressure forces the piston down and produces work energy. That pressure created
by heat and expansion forces the piston in the cooling cylinder down,
which in turn drives the other piston up. This moves the hot gas into the cooled
cylinder. As the gas is cooled it begins to compress, and the pressure in the system lowers.
Compression of the gas causes the piston in the cooled cylinder to move up, driving the heat
piston back down, and forcing the gas back into the heated cylinder where it quickly
heats up, builds pressure, and begins the cycle again.
Check out our two-piston Stirlings here.
The Beta (Type B) Stirling
The displacer-type or 'Beta' Stirling Engine has just one piston, paired with a displacer. In the animation,
the power piston is the upper, and the displacer is deep within the cylinder. The power piston is
tightly married to the cylinder walls, creating the seal that maintains pressure in the system.
But the displacer is loose and allows gas to pass around it. Heat applied to the bottom
of the cylinder creates gas expansion, driving the power-piston up and creating work energy. Because
both the piston and the displacer are attached to the same flywheel, as the piston goes up, the
displacer is driven down. The volume of the displacer now forces the bulk of the gas into the upper
portion of the cylinder and away from the heat source where it can cool. The gas contracts as it cools, lowering
the internal pressure and making it easier for the power piston to move back down and recompress the
Check out our displacer-type Stirlings here.