Nitrous oxide is N[sub]2[/sub]O. When piped to the intake tract of an internal combustion engine, it’s useful for boosting power output because it’s 36% oxygen by mass, whereas atmospheric air is only 20% oxygen; it lets you burn more fuel than you otherwise could.
Nitrogen dioxide is NO[sub]2[/sub]. This is 70% oxygen by mass, nearly twice as oxygen-rich as nitrous. Why is it not being used instead? Cost? Safety? Something else?
NO[sub]2[/sub] is a very reactive substance. It reacts explosively with hydrocarbons, even at ambient temperatures. I imagine that is why.
Checking wikipedia (IANA chemist), sounds like it is TOO reactive. Explosion hazard, used in red fuming nitric acid, and reacts with little things like lung tissue & stainless steel. Heh. Corrosive so you need a heavier &/or more expensive container. Oh, and all the engine parts that contact it would need protection. Whereas nitro is comparatively stable and nonreactive.
I’d also check out “Ignition” by John Clark that talks about working with nitro dio (as red fuming nitric). It is out on the web somewhere as a legal pdf.
I’m not smart on chemistry stuff, but the wiki says that it condenses into a liquid at 70F, so I’m not sure how much of it you could cram into a bottle. N2O can be compressed into a liquid and maintains a steady vapor pressure as it’s consumed, which makes metering it into the engine a piece of cake. That’s one of the primary reasons they don’t just use pure O2 – it’s too expensive to compress it into a liquid, and if you just compress a bunch of gaseous O2 the pressure is going to change as you use it up.
Also, a big part of the power adding effect is that the N2O comes out of the nozzle cold because of the ideal gas law, which means denser gas, which means more boom boom, so the effect is greater than just the percentage of oxygen in the mixture. And it’s already trivial to be able to supply more oxygen than an engine can handle (without grenading) with N2O with standard jets.
In a sense, it is used for that in Top Fuel dragsters, in the form of nitromethane (CH3NO2.) It’s too reactive in its free form, and is a pollutant (it’s an oxide of nitrogen, and ask VW how much people like those floating around.)
But the problem with (NO2-carrying) nitromethane is that it is very prone to detonation in an internal combustion engine, and requires very dense fuel:air mixtures. If you consider gasoline’s stoichiometric air:fuel ratio is ~14.7:1, nitromethane’s is 1.7:1 but race cars will tend to run closer to 1:1 or even 0.9:1 to prevent detonation.
the end result is that these engines burn fuel at such a prodigious rate that a 500 c.i. (8.2 liter) V8 puts out over 10,000 horsepower. Keep in mind that nitrogen really, really, really wants to be gaseous N2 and breaking up that nitro group gets you a big boom.
R/C glow plug engines also use nitromethane as a power booster mixed in with methanol; from 10-15% for airplanes, 25% for cars, and up to 65% nitro for boats.
It would actually be mostly N[sub]2[/sub]O[sub]4[/sub] (dinitrogen tetroxide) when stored under pressure. It’s toxic and fiercely corrosive, but is used in some rocket engines: Proton (rocket family) - Wikipedia
Why the difference?
Cooling. Planes have small cooling fins on the engine, cars have a tall finned cooling head, and boats are water cooled.
I thought cars were harder to cool than planes because prop wash gave much better airflow than the speed of a car. Anyway I’m wandering from the OP.
they are, which is why car/buggy glow engines have such giant finned cooling heads.
here’s a model airplane engine: http://www.modelflight.com.au/equipment/power-systems/air-engines/evolution-36cl-engine-w-muffler.html
here’s an R/C car engine: http://www.modelflight.com.au/equipment/power-systems/engines/losi-350-nitro-engine.html
but there’s another thing in play here (which I left out above) in that R/C planes usually use propellers, and those have a peak effective rotational speed before their efficiency drops. no use adding power boosters to your fuel if you can’t usefully spin the prop any faster. planes with glow-powered ducted fan engines can make use of higher-nitro blends.
an R/C boat engine: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWPH8&P=0
has a water-jacketed cylinder head so it can make use of a lot more nitromethane. some of the more expensive racing engines are getting almost 5 horsepower out of 7.5 cc of displacement.
Yes thats actually why other Nitrogen compounds such as hydrazine are not suitable.
It would be impractical to inject gaseous hydrazine, as it would be too easy to inject liquid hydrazine through the tubes meant to carry gas. If liquid hydrazine pools in the gas pressure regulator , then it might start spitting liquid hydrazine… which is of course far more dense and results in far more thermal energy per unit volume… and greatly changes the ratio of fuel to oxidizer… leaving excess oxidiser… which is unstable and explosive.