There areStirling engines in all kinds of designs.
All current propulsion techniques you find in other engines and machines are also applied here.
The engine consist of two cylinders (A and B) with inside two pistons (C and D). These cylinders form an airtight circuit.
Piston D can also be an elastic diaphragm that will be moved up and down. The power piston has a connecting rod (E). The connecting rod moves the crankshaft around.
The same crankshaft on which a flywheel is mounted moves the displacer piston up and down.
The displacer piston (C) is smaller of diameter than cylinder A, because the air has to pass around the displacer easily.
Cylinder A has a "warm" and a "cold" side. A spirit burner or one or more wax-light candles are used as heat source.
Revolutions around 250-300 refs/min can be reached with a spirit burner.
A special type is the LTD-Stirling engine. The operating principle is the same. Construction is different:
the pressure- and volume differences are created in a box form cylinder.
LTD-engines start turning with a small temperature difference between top- and bottom side. (Low Temperature Difference) Hot water or ice creates temperature- and pressure differences of the gas in the engine.
When friction is reduced to a minimum they even run on body heat.
By cooling the bottom side with ice cubes the engine also starts to run, but than in the opposite direction.