Why pressurized No2/N2O4?

[Idobox]

It appears nitrous oxide is used a lot as oxidant in hybrid rockets, especially in amateur ones. It is also used to "boost" piston engines (ie race cars).

And in many cases, it is stored in pressurized canisters.

So my question is, why use NO2 rather than O2, which gives a better ISP?

Of course, LOx is much more difficult to handle and store than liquid NO2, but I'm not aware of any significant difficulties with pressurized O2.

O2 is cheap, easily available, releases less toxic fumes (depends on the fuel of course) and gives better ISP.

Apparently, NO2 is hypergolic with a number of things, but that shouldn't matter for most rockets (single burn) or cars.

Obviously, for things like satellite attitude control or military applications, liquid NO2 has lots of advantages over LOx. I'm just wondering why would anyone choose pressurized NO2 over pressurized O2

[BananaDealer]

It appears nitrous oxide is used a lot as oxidant in hybrid rockets, especially in amateur ones. It is also used to "boost" piston engines (ie race cars).

And in many cases, it is stored in pressurized canisters.

So my question is, why use NO2 rather than O2, which gives a better ISP?

Of course, LOx is much more difficult to handle and store than liquid NO2, but I'm not aware of any significant difficulties with pressurized O2.

O2 is cheap, easily available, releases less toxic fumes (depends on the fuel of course) and gives better ISP.

Apparently, NO2 is hypergolic with a number of things, but that shouldn't matter for most rockets (single burn) or cars.

Obviously, for things like satellite attitude control or military applications, liquid NO2 has lots of advantages over LOx. I'm just wondering why would anyone choose pressurized NO2 over pressurized O2

For the giggles!

[DonLorenzo]

I'm guessing here, but with NO2 being relatively easy to liquefy and handle in that state the realistic comparison (where ease of use is the prime factor) would be liquid NO2 vs pressurized O2. That would make NO2 more space-efficient than O2 at the cost of every other efficiency metric. Could be it, cryogenics are a ..... after all.

[Sky_walker]

So my question is, why use NO2 rather than O2, which gives a better ISP?

Higher density - boiling point of O2 is -183 °C and for N2O2 it's +22 °C

- so in a room temperature N2O2 will give you higher ISP due to much higher amount of molecules stored that can get in a reaction with fuel,

Cheaper to manufacture in large quantities of high purity gas,

Can be safely stored for a prolonged time without very expensive equipment (assuming you compare identical densities of both gases (which means: different temperatures))

Apparently, NO2 is hypergolic with a number of things, but that shouldn't matter for most rockets (single burn)

Hypergolic fuels got a few more advantages than just ability to reignite. They are more reliable and don't require any sophisticated technology to build a rocket (basically the only thing you need is protection against corrosion and keeping it away from humans (most of the fuels are highly toxic and cancerogenic)), they can sit on a launch pad for much, much longer than cryogenic fuels, and are more stable then cryogenic fuels, so transportation is cheaper and less risky.

[xenomorph555]

I remember peter madsen saying something about creating instabilities and being less efficient somehow.

[lajoswinkler]

Nitrous oxide is nitrogen(I) oxide or N₂O - it is used for whipping cream, in dentistry (not so much anymore, and rarely outside anglosaxon world). It is weakly toxic. Colourless.

Nitrogen(II) oxide or NO is a very poisonous gas which immediately reacts with air. It has a purpose in our bodies as a vasodilator. Colourless.

Nitrogen(IV) oxide or NO₂ is very poisonous orange gas which, when reacted with oxygen and water, gives nitric acid.

There are more oxides, but these three are the most important.

Only nitrogen(I) oxide is used in cars. Other oxides would result in damage to the engine and a very toxic and corrosive exhaust.

[QuesoExplosivo]

For rocket oxidizer, dinitrogen tetroxide (N₂O₄) is often used. This is a dimer of NO₂.

This is, as lajoswinkler stated, very different from N₂O, which is also used in rockets.

Edited July 25, 2014 by QuesoExplosivo

[Rakaydos]

Burning a nitrogen/oxygen bond with a fuel generates more ISP than an oxygen/oxyge bond, because it allows two nitrogen atoms to bond into N2, a reaction that by itself generates quite a bit of power.

[K^2]

Higher density - boiling point of O2 is -183 °C and for N2O2 it's +22 °C

- so in a room temperature N2O2 will give you higher ISP due to much higher amount of molecules stored that can get in a reaction with fuel,

This warrants a clarification. By itself, density doesn't enter into I_SP, since you only care about the weight of the fuel/oxy. But pressurized O2 means you have to carry a huge pressurized tank as dead weight. If you add that weight to the weight of your fuel/oxy, you do, indeed, get better effective I_SP even with straight up liquid N2O.