Acetylene mixed with nitrous oxide...

[joannaardway]

N2O stores loads of energy in it's structure, whereas oxygen stores none in it's structure. However...

In a pure 1 litre mix of air and 4% propane (yes, it's not acetylene, but the maths is easier - and the results will be similar), then there are 3900 J of energy available.

In a pure 1 litre mix of oxygen and 20% propane, 18500 J of energy are available.

In a pure 1 litre mix of nitrous and 10% propane, then 12660 J of energy are available - less than oxygen, because the amount of energy available from the propane is less.

The reason nitrous is used in cars/other stuff, is the easier storage - nitrous can be stored in liquid form (like CO2 or propane), whereas oxygen can't be stored easily, and has to be stored as high pressure gas. (N2O can also be injected to help cool the engine to help prevent overheating from the extra energy)

So it's better than air in energy terms, but less good than oxygen, but is the easier storage option.

So if you can, use oxygen. If you can't store that, use nitrous oxide.