Here's an engine rarely seen since they were only ever designed and intended to be disposable. This is the 4 cylinder radial engine from a WWII German G7A torpedo. It ran on Decaline fuel (decahydronaphthalene), which was first burned. The combustion byproducts were then passed through a device called a 'wet heater', which also introduced water (from a 57L onboard storage tank) to produce superheated steam. This high pressure mixture of superheated steam and compressed air was finally sent through the engine to drive the pistons.
Since the internal combustion/steam generator system was self-contained and fueled by a chemical reaction instead of ambient air, it could run underwater. The 4 cylinder, 'X' type radial engine produced up to 350 horsepower at its maximum power setting, which was enough to push the 26',6" torpedo (the length of a large Uhaul moving van for comparison purposes) along at nearly 50mph while submerged.