Hard tech question: n2o vs NitrOx

I’ve got a question for some of the more Chemistry minded folk.

I’ve recently entered the world of SCUBA diving. Those of you who are divers will be familiar with Nitrox. For those who aren’t I’ll describe it.

Normal air is basically 21% Oxygen (O2) & 79% Nitrogen.
Nitrox is just a mix of Oxygen & Nitrogen with the Oxygen levels increased. The most common mixes are EAN32 (32% O2) & EAN36 (36% O2).
Most fill stations are also capable of doing custom mixes.

Here’s where I’m going with this if you haven’t already guessed.

N2O breaks apart into Nitrogen & Oxygen (33% Oxygen by # of molecules, 36% by atomic weight). So it basically becomes EAN36 once inside the combustion chamber.

An 80cu/ft tank cost’s $6-$10 to fill with Nitrox at most fill stations. That’s about 6 ½ lbs of gas. Pretty cheap.

The cost of filling up the bottle is the main drawback to a N2O setup. That’s the only reason I’m interested in exploring this possible option.

Here are the main differences between the two gasses:

#1. N2O is in liquid form in the bottle, Nitrox is still a gas (even @ 3000psi in a SCUBA tank)
- So there would be no state change, which means no cooling effect.

#2. The O2 is already free in Nitrox.
- Not sure if this would cause any pre-ignition problems, or if the O2 percentage is low enough not to cause problems.
- I’m not sure about this, but I would imagine N2O uses heat energy when it’s broken apart, which is another cooling effect that would not exist with Nitrox.

So those of you who have some good chemistry knowledge, what would be the effects of using Nitrox in a Nitrous system type setup?

(Please no, “Just use N2O it’s proven to work, it’s not worth saving a few bucks every fill up” type responses. I’m looking for some legitimate information / arguments. )

I'm not the the most scientific mind on this forum by far, but I'll throw my .02 in.

I have never heard of that Nitrox that you descirbed until now. It sounds like a good idea at first, however, you yourself stated the downfall of the gas and why I would not use it. Here-

- So there would be no state change, which means no cooling effect.

- Not sure if this would cause any pre-ignition problems, or if the O2 percentage is low enough not to cause problems.

If I had to guess, and I am:D , I would say that there could definately be the possibility of some pre-ignition problems occuring.

The other thing is, automotive grade nitrous consists of more than JUST nitrogen and oxygen. I know for sure they have some type of sulfer(sp) added in and I think something else. I have done some reading on the differences between the medical and automotive grades of N2O but its been a little while and I can't remember exactly why the extra gasses are added, but they ARE needed nonetheless.

I wish I had my nitrous booklette I recieved with my kit. It gives some really good information believe it or not, including the different types of N2O, history of N2O, and, why you should use the recommended automotive grade instead of trying to figure out other ways to accomplish the same thing, but with a slightly diiferent type of gas. I would really like to be able t reffer to it.


I guess I'm not much of a help, maybe someone else could chime in and offer a more educated opinion...



Jon

The sulfur in auto grade nitrous is 50-100ppm, which is an insignificant amount. It just there to smell bad, and irritate your lungs when you try and inhale it. It in no way alters the chemistry in the combustion chamber.

Having 3,000psi gas-phase O2/N2 in a tank would mean that you would have very little contained in a bottle the same size as a 10# nitrous bottle, and the bottle would have to be even heavier than the nitrous bottle, since it will have a 3,000psi working pressure rather than an 1,800psi working pressure. I don't know if your estimate of 6.5# in an 80cu ft bottle is correct, but if it is, you would need a pretty big bottle just to make a single pass. I estimate a 10# nitrous bottle as less than 0.5cu ft, so at the weight you quote (6.5#/80cuft), you would need the equivalent of twenty 10# nitrous bottles to make a single pass (assuming 1# consumption).

And the lines would all need to be larger, since it is in a gas phase rather than a denser liquid phase. And, since it is gas phase with little cooling effect (there is some heat absorbed as the gas expands from the 3,000psi state to the atmosheric pressure state, but nowhere near as much as the phase change when nitrous goes from a liquid to a vapor), you would not gain that advantage of the traditional nitrous system, and it is appreciable.

Somebody could check my weight/volume calculations, or your quotes to see if they are correct.