How Stirling Engines Work 

Stirling engines can be hard to understand. Here are the key points. Every Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side it expands and pushes up on a piston.

When it moves back to the cold side it contracts. Properly designed Stirling engines have two power pulses per revolution, which can make them very smooth running.
Two of the more common types are two piston Stirling engines and displacer-type Stirling engines. The two piston type Stirling engine has two power pistons. The displacer type Stirling engine has one power piston and a displacer piston.

Displacer Type Stirling Engine

Displacer Technical IllustrationThe displacer type Stirling engine is shown here. The space below the displacer piston is continously warmed by a heat source. The space above the displacer piston is continously cooled. The displacer piston moves the air (displaces the air) from the hot side to the cold side. The Coffee Cup Stirling engine is this type of engine. However, the Coffee Cup engine should never be warmed with any heat source hotter than boiling water.

Click the following links to see the principles of operation of the two-piston type Stirling engine:

Still Illustrations (about 20K)
Animated Illustrations (about 130K)
 

Two-Piston Type Stirling Engine

2 Piston Technical IllustrationThe two piston type Stirling engine is shown here. The space above the hot piston is continuously warmed by a heat source. The space above the cold piston is continuously cooled.

Click the following links to see the principles of operation of the two-piston type Stirling engine: 

Still Illustrations (about 12K)
Animated Illustrations (about 130K)