Stirling Engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas. This model uses air heated by the meths burner on the right. It is remakably free running and quiet.
Robert Stirling invented this type of engine in 1816 and they are seeing a resurgence of interest for potential use in combined heat and power microgeneration systems owing to their high levels of efficiency. I guess it's a case of what goes around comes around!