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 gas.

Check out our displacer-type Stirlings here.