Operation of the ST-5

The ST-5 operates on the temperature difference between its hot and cold ends. At one end is the heater head which is inserted in a burner; at the other, the cooling jacket and crankcase. These are the three components of the engine body which contain air, pressurized to 5 bar (approximately 72 p.s.i.) by a built in air compressor.

When heat is applied to the heater head by burning some combustible material in the burner, the air contained in the head is caused to expand and move to the cold end through a heat sponge call a regenerator. At the cold end, the air is cooled and compressed, and is then moved back to the hot end again though the regenerator. The purpose of the regenerator is to improve efficiency by absorbing heat when the air is shuttled to the cold end and releasing heat when the air returns to the hot end.

When the air in the hot end expands, it produces work which drives the piston towards the cold end. At the end of the piston's stroke, the displacer is moved by a mechanical linkage which pushes the expanded gas through the heater, regenerator and cooler into the cold end. The piston now returns from the end of its stroke, compressing the cold gas, and the displacer moves down towards the piston, squeezing the compressed gas in a reverse direction through the heat exchanger loop to the hot end. The cycle then repeats itself. This linear movement of the piston is converted into the rotary movement of the flywheel by means of a simple linkage contained in the crankcase. The crankcase has been designed to run dry, not needing any oil or grease. The bearings in the linkage are sealed and require no lubrication.

The only moving parts in the engine are the displacer, piston and linkage. This is what makes the engine extremely reliable and easy to service and maintain.