Apparently they make cars that run on natural gas. Where do you even _get_ that fuel?
@Motodrachen You probably don't want to be filling the gas tank with actual gaseous gas. That wouldn't work out very well.
I'm sure they run on LPG, and now that I've actually considered that a bit I think we have seen things like buses and semi trucks that run on LPG. It's weird to see a sedan that does though.
@Motodrachen I can't imagine liquifacted coal would make for a good fuel for an internal combustion engine, though.
@Motodrachen I've seen ammonia mentioned as a possible cleaner-burning fuel before. How does that compare, or does it need to use a completely different thermodynamic cycle?
@Motodrachen As we understand it, the main obstacle to using ammonia as fuel is the fact that it produces extremely noxious combustion byproducts; the ideal reaction would be 4 NH₃ + 3 O₂ → 2 N₂ + 6 H₂O, but the actual reaction produces substantial amounts of mixed nitrogen oxides that need to be dealt with
It's kind of interesting, but I don't think it's a workable fuel, especially not as an environmentally friendly one. You'd need big catalytic converters.
@Motodrachen I think the problem is that it gets too hot and oxidizes the nitrogen beyond N₂. Because nitrogen in ammonia is already reduced to the -3 oxidation state, and then your clean combustion gets it to the 0 oxidation state in N₂, and then things like NO has +2; you've over-oxidized the nitrogen and in the process also consumed some of the energy that would otherwise have gone to propulsion
@Motodrachen I think the idea is that it'll be possible to avoid that by controlling engine temperature, but it seems like a bit of a lost cause to me. It's an interesting thought, though, to use a fuel that you can make from electricity, air, and water.
@Felthry @Motodrachen I could see that having application in ship engines, maybe. Use the hull as the warm side of a coolant loop.