External Combustion

• A Stirling engine can use almost any heat source for power. External sources of heat and cold drive the engine's cycle.
  
  

Mechanism

• A simple Stirling engine consists of two pistons, expansion and compression, at either end of a common sealed tube. The pistons are connected to a rotary drive. When one piston is fully in, the other is halfway out.
  
  

Working Fluid

• Air or another gas is the engine's working fluid. The gas is permanently sealed inside the engine.
  
  

Cooling Cycle

• The gas enters the cold half of the engine, contracting and pulling the expansion piston in. The rotary mechanism turns, pulling the compression piston in and pushing the expansion piston out.
  
  

Heating Cycle

• Cold gas flows back to the hot half of the engine, where it's heated. The heated gas expands, pushing the expansion piston fully out. The mechanism turns, which moves the expansion piston in and drives it back to the cold half, continuing the full cycle.