[DoctorOetker]

N2O (laughing gas) is not combustible, but autodecomposes into a mixture composed of 1 part oxygen gas and 2 parts nitrogen gas, which happens to be the approximate composition of the atmosphere.

In theory we could design and use N2O engines and airplanes etc, and their exhaust could be a gas that is nearly equivalent to atmospheric composition.

One important issue is making sure all the N2O has decomposed because it is a very potent GHG.

Would N2 and O2 create contrails? in what sense is it distinct from atmosphere?

[cyberax]

N2O formation enthalpy is just 82kJ/mol. For comparison, water is 240kJ/mol.

It doesn't sound so bad, but when translated into grams, it's 1.86kJ/g for N2O and 13.3kJ/g for water.

In other words, when burning a gram of hydrogen, you get about 120kJ of energy. When decomposing a gram of N2O, you barely get 2kJ.

[saagarjha]

You’re off by a factor of 10 somewhere

[cyberax]

Nope? A gram of water is mostly oxygen. Hydrogen is just 2/18 of the water mass, so that's where the factor of 9 comes from.

[klodolph]

Someone can break out their chemistry references, but I think N₂O is probably not workable as a fuel (or at best, not very good). It forms naturally in internal combustion engines, from air, at the temperature and pressures found in engines, given O₂ and N₂. If something has the habit of forming in an engine, I don’t think you could use it as fuel, but my thermodynamics is a bit too rusty to do any kind of ELI5 and I could just be wrong here. At the very least, it would be difficult to use or inefficient.

It decomposes into N₂ and O₂ at normal atmospheric temperatures and pressures, outside an engine.

[topaz0]

You're probably thinking of NO2, which is indeed a pollutant that results from overly hot combustion in air. N2O is in fact used in engines, but it is not the fuel -- rather it is a supplementary oxidizer, which allows you to burn more fuel and therefore produce more power than you could if you only had the oxygen from air. At any rate, that means using N2O won't be a solution to the aircraft fuel problem -- you'd still need a combustible fuel for it to oxidize.

[DoctorOetker]

You are correct that N2O is the "nitro" afterburner used in different systems.

But the reaction 2 N2O => 2 N2 + O2 is very exothermic, in fact it is explosive (but not in the burning sense, since its autodecomposition). However adding a small amount of ethanol makes N2O stable so that sudden shocks or compressions don't result in initiating autodecomposition or explosion.

To power an engine one doesn't necessarily need to burn, or a redox reaction to happen, the reaction just needs to be exothermic and N2O is very exothermic.

[topaz0]

I stand corrected.

[klodolph]

Damn, yes, I mixed those up.

[LargoLasskhyfv]

Fume events would be more funny, then!