In the family of heat engines, “Stirling engine” is defined as a “closed-cycle regenerative hot air engine”. In this context, according to Wikipedia, “closed-cycle” means that the working fluid is permanently contained within the system, whereas “open-cycle” engines such as internal combustion engine and some steam engines, exchange working fluid with their surroundings as part of the cycle. “Regenerative” refers to the use of an internal heat exchanger. In contrast to internal combustion engines, Stirling engines have the potential to be more energy efficient, quieter, and more reliable with lower maintenance requirements.
Was that enough engine nerdiness for you? No? Then do I have something for you.
The Stirling Engine Kit is a great little gadget that will run off the residual heat off your body or any other warm surface it comes into contact with. You can see with your own eyes the functionality that made this engine, at the time, a serious alternative for the internal combustion engine.
Now with global warming and people getting interested in alternative fuel and energy sources, it may be a good idea to look into this technology once again. From Wikipedia:
In recent years, the advantages of Stirling engines have become increasingly significant, given the general rise in energy costs, energy shortages and environmental concerns such as climate change. These growing interests in Stirling technology have fostered the ongoing research and development of Stirling devices. The applications include water pumping, space-based astronautics, and electrical generation from plentiful energy sources that are incompatible with the internal combustion engine, such as solar energy, agricultural waste and domestic refuse.
Not too shabby. You can pick up your own palm-sized marvel for yourself for $49.99.