The pressure chamber contains a small amount of air that is held captive inside the engine. One end of the engine is warm, and the other end is cool. The displacer moves the air inside the engine back and forth repeatedly, from warm, to cold, and to warm again.
The air inside the engine expands when it gets warm, and pushes outward on the drive mechanism. When this same air is moved to the cool side of the engine, it contracts. This pulls in on the drive mechanism.
The drive mechanism pushes and pulls on the crankshaft. This causes the crankshaft and flywheel to rotate. The rotation of the crankshaft causes the displacer to rise and fall inside the pressure chamber.
The crankshaft is fashioned so that the cycle will repeat. The air heats, expands, and pushes the crankshaft through the expansion phase. This moves the displacer and causes the air to enter the cool side of the engine. The air cools, contracts, and pulls the crankshaft through the contraction phase. This starts the next expansion phase and the pattern continues to repeat itself.
Stirling Engine Parts
This drawing illustrates the basic parts of a Stirling engine. The pressure chamber contains air that is held captive in a closed system. The air is heated when it is on the bottom of the pressure chamber, near the flame. The air is cooled when it is on the top of the pressure chamber. The air is moved about inside the pressure chamber by a loose fitting piston called a displacer.
The drive mechanism pictured here is a piston. In many cases it is a rubber diaphragm. They both accomplish the same thing.
The crankshaft and the flywheel keep everything moving in sync.
When the engine is in the warming phase, the air is in the warm side of the engine. This causes the air to expand, which pushes the drive mechanism upward.
When the engine is in the cooling phase, the air is on the cool side of the pressure chamber. The air contracts as it cools. This pulls down on the drive mechanism. The repeated pushing and pulling of the drive mechanism causes the crankshaft and flywheel to rotate.