A stirling engine is a heat engine which operates by an expansion of air and cyclic compression at different temperatures.
More specifically, a stirling closed-cycle regenerative engine that has a permanent gaseous working fluid. What’s more interesting is that you can build one on a low budget. All that with no fancy tools.
All you need to build a soda can stirling engine is a balloon fishing line, 2 empty cans, a grinder disc for the flywheel, 3 electrical connectors and some wire. Check it out!