Which fuel could not be used easily for powering cars?

coal, the others can be. I built an engine that would run off water in the early 70's, you need to "crack " the water by electrolysis into hydrogen and oxygen, it is then pumped into the cylinder and ignited resulting in an explosion that will drive the piston, the piston scrs will then remove the water back into the tank. Had it running for about 6 hours but it was very underpowered.