Miniature Stirling Engine Has Visible Working Parts, Runs on the Heat from a Cup of Coffee! This precisely constructed Stirling Cycle engine is designed to work on small temperature differences. With the body of the engine at room temperature, exposing the aluminum base of the working cylinder to condensing vapor from hot water or placing it on ice is enough to set it running for many minutes. All the working parts of the engine are visible. The piston is a flexible silicone diaphragm that expands and contracts as the air in the cylinder is pushed back and forth by a foam displacer piston between the hot aluminum base plate and the cold body of the engine. Model allows you to explain the workings of the engine and the thermodynamics of the underlying Stirling Cycle.