@Nomaxice I would guess natural gas refers specifically to LPG, since having it actually stored as a gas would be inconvenient to say the least

There must be some in the US, as there are cars available here that use it, but I've never seen a gas station that offers it

I think I have heard of buses using LPG before though now that I think of it, so maybe fueling stations that focus on trucks and buses would be more likely to have it.

@Felthry That's it yep! Or "GPL" in french.
My stepfather had a car that was "hybrid", could run on regular gas or LPG, and I know he refueled it at least at a supermarket gas station that offered it, pretty sure I could try and find more with an online search.

@Nomaxice That's a lot more reasonable than what my first thought was, which was using natural gas in its actual gaseous state.

Nowadays I imagine those "hybrids" would correspond to the modern flex-fuel cars? Do they still make small vehicles with LPG/GPL engines over there?

@Felthry I think you can still find some LPG powered vehicle but they're pretty rare, I'm afraid I can't really provide more knowledge on that

@Nomaxice That's fine! I'm asking out of curiosity, not any actual need to know.

@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.

@Motodrachen Incidentally, have you ever looked at bob's mods for factorio? THAT is the real demonstrator of how difficult processing stuff gets.

@Motodrachen I appreciate the circuitry stuff it does. Needing to etch circuit boards and produce components just appeals to me.

I kinda like the metallurgy aspects too, but I think I'm in a minority among our friends. Processing ores in more realistic ways, and being able to use byproducts of other manufacturing processes to extract more metal, just appeals to me.