Hot bulb engines

The two videos above are of hot bulb engines. The top video is of an exquisite model of a hot bulb engine, while the bottom video shows one operating on and old fishing boats.

Hot bulb engines were popular when gasoline engines were still being developed and they were used through the early 1960s. They can be fueled by virtually any combustible liquid and can run for a long time. However, they put out low RPMs, 300 is about their maximum, so their main use was pumps, mills and on boats.

They're unique internal combustion engines in that their combustion chamber is separate from the piston's cylinder. The combustion takes place in the 'hot bulb', which has its sides heated. Fuel is drawn in where it vaporizes and mixes with air and it ignites because of its heated walls. This forces exhause gas down a tube which drives the cylinder. 

A good explanation of the process can be found at: How a Hot Bulb Engine Works.