This is a German made Bohm HB14 Stirling engine.  It is known as the “Big Bonsai”.  Power and energy pour from this machine via a double overhead cam. 

Do you know how this fascinating machine works?  The principle is very old, yet very simple.  Just put a little flame under the piston and give the fly-wheel a spin and watch this machine work - getting faster and faster.  To understand the functional principle of such engines, the working cycle can be simplistically described as follows: 

The power piston and the displacer piston are connected to the crankshaft in 90 degree phases.  The air in the cylinder of the displacer piston is heated by the burner.  The heat creates expansion of the air volume therefore starting the working pistons and the flywheels in motion.  As the working piston moves outwards, the displacer piston is pushed into the heated cylinder.  As a result, the heated air is pushed into the cooled part of the motor, creating a fast cool down and decrease of the air volume.  The decreased air volume shoves the power piston back into the cylinder and keeps the flywheels in motion.  The rotary motion causes the displacing piston to be retracted outwards while cooled air streams into the space above the flame.  The air becomes heated and expanded again therefore beginning the new cycle.

Bohm HB14 Stirling Engine