The Flame Eater Engine
A Vacuummotor, also called the flame eater, is a hot air motor but not a stirling motor.
The principle is quite old. In 1758 Henry Wood already was granted a patent.
From the technical point of view it is an atmospheric motor, because the outer air pressure does the work (comparable to the first Ottomotor). The piston sucks the flame into the cylinder through an open valve (causing a running noise, which reminds you of a Lanz Tractor) and the heats the air inside. While the piston goes back the valve closes, the air in the cylinder cools down and the outer now high atmospheric pressure presses the piston forward. Therefore the maximum power of the piston is limited to the product of the surface of the piston x air pressure. When the piston reaches the front dead center the valve opens again and the game starts again, a flywheel comes forward carrying the engine through momentum of both dead centers. Used a fuctioning motors for models they are often build as stationary motors in horizontal and vertical versions and as single, double or multi cylinders. They have been used for models of nostalgic tractors and rail vehicles very successfully.