How does it work?

The Stirling engine surprises by its simplicity, since it consists of two chambers at different temperatures that heat and cool an alternative form of gas, causing an expansion and a cyclical contraction, which makes moving two pistons connected to a common axis. To reduce heat losses, a "regenerator" is installed between hot and cold chambers, where the heat (which would be rejected in the cooler) is stored for the next stage of heating, increasing the thermodynamic efficiency.

The gas used in the simplest models is air. In versions of high power and efficiency, pressurized helium or hydrogen for gases are used, which have higher thermal conductivity and lower viscosity, we’re saying, carry thermal energy (heat) faster and have lower resistance to deflation, which implies less friction losses. Unlike internal combustion engines, the working fluid never leaves the interior of the engine chamber, it is therefore a closed-cycle machine.

Summarizing the Stirling engine works by using the difference temperatures in gas and its consequent contraction and expansion.