# Plausibility of a car running on noble gasses

Is there any science-based way that one could explain cars running not on natural gas (autogas) but rather on noble gasses like Neon, Argon and/or Xenon?

Noble gasses are called "noble" because they don't interact with other elements (same way as nobility of the past didn't mix up with lower classes).

Since the entire concept of combustion engine works around chemical reaction, it follows that no combustion engine can work using noble gases, because there would be no way to get energy out of them.

However:

• you can still run an engine on compressed noble gas rather than compressed air. It will just be more expensive than compressed air.
• helium and neon are the only noble gases which can undergo fusion (I haven't found evidence that argon and xenon can undergo fusion), but that requires conditions similar to those found in stellar cores to happen (for neon, it need stars with more than 8 solar masses).
• You can fuse argon too... only happens in the very late stage of big stars as part of the alpha ladder, but it does happen. $\require{mhchem} \ce{^36_18Ar + ^4_2He->^40_20Ca}$ Apr 8, 2022 at 15:23
• All elements can be fused to heavier elements. For elements with an atomic mass below that of iron, the fusion produces energy. For elements with an atomic mass above that of iron the fusion consumes energy. Elements heavier than iron are generally only produced in large(ish) amounts when a star goes nova or super nova. Fusion of noble gases up to argon (helium. neon, argon) should produce energy. Krypton and above will consume energy.
– JRE
Apr 8, 2022 at 19:02
• Krypton and Xenon could maybe be fissioned to release energy, but it'd be really hard. Radon naturally decays and gives off energy, and is maybe fissile. Going down the chart one more to Oganesson, and it's... decidedly more radioactive and would only be storable for milliseconds. Apr 8, 2022 at 19:13
• Fusing two $^{40}_{18}$Ar to make $^{80}_{36}$Kr does release energy. Just really hard to get over the Coulomb barrier. Apr 8, 2022 at 21:34
• Right, any element can be fused if you have a sufficiently large star to do the work for you (or maybe a supernova for the larger ones). However, a star the size of Rigel does not seem like a practical component for a car engine. Apr 9, 2022 at 12:17

## You need a new technology

I assume you've chosen noble gasses because they're completely unreactive. The flip side of that is that they would release a lot of energy, if they were somehow in the wrong state to start with.

Let's suppose you have a car based on an ultracapacitor - instead of batteries, it stores all its energy in a separation of charges. Now to be sure, what I'm thinking of here straddles the boundary with a liquid-state battery or maybe a Bose-Einstein-state battery; maybe you'd call it that instead.

One 'electrode' consists of a cloud of Ne2+ ions - absurdly reactive, just want to be neon again. The other 'electrode' is more prosaic, maybe O- groups attached to a substrate. It can readily shift back and forth between having the oxygens with negative charges on them or being a peroxide.

The trick is layering these electrodes right next to each other, without the juicy lone pairs on the oxygen being gobbled up by the desperate neon atoms. Here's where you need some new technology. What if the neon ions are in, I dunno, maybe a Bose-Einstein condensate, with a delocalized state that perpetually orbits the negative charges on the oxygen without ever quite going in. Or maybe you use some kind of infrared/microwave light to keep them from getting too close. Instead the neons are deducted at a far point, taking electrons routed around from the back of the oxygen electrode.

This is 90% handwaving, 9% bunkum, and 1% mechanically recovered chemistry meat, but a lot of sci-fi books and shows don't have that much, so there's that.

• Crazy BS, but really FUN BS. I like it! +1 Apr 9, 2022 at 1:12

https://en.m.wikipedia.org/wiki/Ion_thruster

Noble gasses used in sattelite engines to correct orbit. Those are low power engines, and only work in vacuum.

If your setting is based in space, and there is plenty of energy in mobile sources, then cars (or rather small spaceships) could use noble gasses to run around some space city. Keep in mind, this engine still needs large energy input. Batteries can barely fit, short term only.

Noble gasses are used because heavy atoms are required, that also dont stick to themself.

Apart from that: no. I dont see any practical usage for transport. Compressed gas storage is very low power density. Cryogenic storage is especially hard with nobble gasses as they need low temperature. Noble gasses arent good for fission or fusion. They are also expensive.

• Noble gasses are used because they're not too difficult to ionize, which is a big energy sink for ion thrusters. Mercury propellant is trickier but the engineering issues have basically been solved now. It does have some environmental concerns that have lead to the UN calling for it its use as a propellant in Earth orbit to be banned. Metal propellants avoid the need for heavy pressure vessel storage, though. Apr 8, 2022 at 15:32
• Why would a space city require its inhabitants to use rocket engines to get around, instead of having roads or tracks or cables or something for vehicles to run on? Apr 8, 2022 at 18:59
• @TannerSwett because it is a dyson swarm, or other non-connected set of objects Apr 8, 2022 at 19:03
• Using ion engines for car-like spaceships (i.e. in a dense area and steered individually) sounds dangerous – the amount of time you need for braking (or changing direction) is really too large for this. Apr 10, 2022 at 23:37
• @PaŭloEbermann unlike all other answers, there exist at least a world where this is optimal - scarcery populated space with disconnected structures. There is zero sense in ever using pressurised noble gas for a movement (price is extreme, energy close to 0), or using nobble gas for chemistry (almost 0 energy) or using fusion engine based on noble gas (always better alternatives). Is my answer bad? Sure. But it is the least bad of all answers. And author limited the scope to this. And if i answer outside the scope - mod (dutch) just deletes my answer. What do you want me to do? Apr 11, 2022 at 0:13

## It is possible but very impractical

Xenon has over 100 compounds identified that it can form to release low energies. Xenon difluoride for example releases −108 kJ·mol−1 on formation. This is not a lot of heat, but it is heat, and could produce usable work. A usable vehicle would be highly unlikely, but for a lot of fuel, it would move a short distance.

There are no known high energy compounds with the noble gasses, as yet.

• RE Xenon diflouride: The problem is that it implies that you have a source of fluorine, which combines with more than half of the periodic table much more energetically. Apr 9, 2022 at 12:22
• @RBarryYoung There are many many problems with the OP world in general, but “impossibility” wasn’t one of them. So, I wish them good luck Apr 9, 2022 at 21:44

Good luck containing the ultra-hot, ultra-dense helium needed for the triple alpha process. You're not going to get chemical energy out of them so you have to go nuclear--and that's the easiest one to do. (Hint: The center of the sun doesn't do it meaningfully.) It's aneutronic and emits only gamma rays so there is no lingering radiation to deal with.

You also could have helium-argon and argon-argon fusion, both are likewise free of lingering radiation, but they require even more extreme conditions. Going farther down the table you're not going to find energy until you get into the fission realm.

I agree with the answer of L.Dutch, however depending on the technology level, you can also consider small scale nuclear fusion. (Probably an overkill though...)

• I had been considering that but seeing how i want at least a little plausible realism i had the same concerns that stopped nuclear cars in real life. Wouldn't the nuclear radiation endanger the driver and passengers in the long run? (think Ford Nucleon) Apr 8, 2022 at 10:14
• yes, they'd probably have radiation. not necessarily dangerous to the passengers, but in case of an accident very likely. euro-fusion.org/faq/top-twenty-faq/… Apr 8, 2022 at 10:43
• @BlueDevil "it depends". Depending on the reactor design and fuels used, there can be less prompt radiation and much less long term radiation in a fusion plant. It might be worth asking a separate question on that subject, if you were interested. Apr 9, 2022 at 16:15

Further to other answers, it isn't strictly true to say that noble gases don't ever form compounds, although they are famously unreactive and would be unlikely to make a good fuel in their pure form. The heavier noble gases can react with highly reactive species.

For example, xenon can be made to react with fluorine to form several fluorides, from xenon difluoride (XeF2) to the hexafluoride (XeF6). The reactions are endothermic, so to get energy out to run a vehicle you'd need to start with the fluoride and break it down. Your exhaust would probably include pure xenon (or whichever noble gas you use) so you might just get away with describing the vehicle as "running on a noble gas".

There's a brief discussion here on the plausibility of using noble gas halides as rocket fuel. The first example produces HF in the exhaust, which would be bad news in a car - HF has some nasty effects on living things.

Helium (a noble gas) undergoes fusion with oxygen to make Neon (another noble gas). Although this only happens naturally within a star, I suppose you just need to supply your Mr. Fusion (Back to the Future) with Helium to have a car powered by a noble gas.

Well, we don't know how the "car" functions. While most answers focus on using a noble gas as a fuel (which leads to nuclear fusion) or as a working gas, there are other options.

# Coolant

Your (very hand-wavy, I must admit) car engine uses something else as a fuel. It might be a fission reactor, eezo, unobtanium, whatever. The key characteristics of this fuel is that you need so little of it, that no frequent recharging is required.

However, the way this engine is built, a more conventional cooling system (based on a radiator that dissipates into the surrounding air) is not sufficient. It is not economic / does not fit the usage model to carry some water tank for evaporation either.

Instead the manufacturer of the "car" sells coolant cartridges, filled with a liquified noble gas (say, Helium). You have your gas stations and inkjet cartridges back, now for super-engineered cars, great business success!

To elaborate, the actual fuel source is eternal or at least not user-maintainable. But instead of a more sane cooling solution, some cryogenic-level stuff is used to bind the user to the supply chain. The novel engine, the novel isolating material for cryogenic dewars with Helium, all this is rather handwavium. As the whole system is rather over-engineered and makes only commercial sense, at least I hope those "cars" are fast!