An engine made of water

EVERY so often someone tries to design a new internal-combustion engine. Few make it from the laboratory bench to the big bad world. The last serious attempt, Felix Wankel's rotary engine, lingers on in Mazda's sports cars and is also used to power snowmobiles. But it suffers from a fatal flaw, which is that the tips of the rotating piston on which the device relies tend to become worn. What if—do not laugh—the piston were made of water?