bohm

For understanding of the functional principle of such engines the working cycle can be simplistically described as follows:
Working piston and displacer piston are connected (a phase angle of 90° is needed) with the crank shaft. The air in the cylinder of the displacing piston will be heated by the burner. The heat effects an extension of the air-volume and through that the working piston and the flywheels start to move. First the working piston moves outwards while the displacing piston will be pushed into the heated cylinder. Thereby the heated air will be pushed into the cooled part of the motor which effects a fast cool down and decreasing of the air-volume. The decreased air-volume effects that the working piston will be pushed into the cylinder and thereby run the flywheels. The rotary motion provides that the displacing priston will be retracted outwards whereby the cooled air streams into the space above the heating.
There the air will be heated and extended again and the process begin a new.