Nitrous oxide is an oxygen bearing compound. Its chemical designator is N2O, so we know each nitrous oxygen molecule has two nitrogen atoms and one oxygen atom. Nitrous oxide is sometimes incorrectly known as "NOS". That is an acronym for the company, Nitrous Oxide Systems, which is the largest marketer of nitrous oxide injections system for automotive use.
When you heat nitrous oxide to about 565 degrees F (~300 C), it splits into oxygen and nitrogen. So the injection of nitrous oxide into an engine means that more oxygen is available during combustion. Because you have more oxygen, you can also inject more fuel, allowing the same engine to produce more power. Nitrous oxide is one of the simplest ways to provide a significant horsepower boost to any petrol engine. Nitrous oxide has another effect that improves performance even more. When it vaporizes, nitrous oxide provides a significant cooling effect on the intake air. When you reduce the intake air temperature, you increase the air's density, and this provides even more oxygen inside the cylinder. The only problem with nitrous oxide is that it is fairly bulky, and the engine needs a lot of it. Like any gas, it takes up a fair amount of space even when compressed into a liquid. A 5-litre engine running at 4,000 rpm consumes about 10,000 litres of air every minute (compared to about 0.2 litres of petrol), so it would take a tremendous amount of nitrous oxide to run a car continuously. Therefore, a car normally carries only a few minutes of nitrous oxide, and the driver uses it very selectively by pushing a button
Today nitrous oxide injection, like many other modifications such as more aggressive camshafts, bigger carburettors, higher compression ratios, more free flowing intake and exhaust systems, can be a practical way to more horsepower. And like any other modification...perhaps even more so because it so easily lends itself to misuse...there can be a reliability and durability price to pay.
When Nitrous is introduced into the intake tract of an internal combustion engine, it is sucked into the combustion chamber and, on the compression stroke, when the charge air temperature reaches 565 deg., a very oxygen-rich mixture results. If we add extra fuel during nitrous oxide injection, the effect is like a super charger or increasing the compression ratio of the engine. Automotive nitrous systems work like the automotive equivalent of a jet's "afterburner" and is used for short duration extra bursts of power.
Nitrous oxide has this effect because it has a higher percentage of oxygen content than does the air in the atmosphere. Nitrous has 36% oxygen by weight and the atmosphere has 23%. Additionally, nitrous oxide is 50% more dense than air at the same pressure. Thus, a cubic foot of nitrous oxide contains 2.3 times as much oxygen as a cubic foot of air. Just do a bit of maths in your head and you can see if we substitute some nitrous oxide for some of the air going into an engine then add the appropriate amount of additional fuel, the engine is going to put out more power.
Simply stated, nitrous oxide injection is very much like a supercharger or a compression ratio increase in that, during combustion, it can dramatically increase the dynamic cylinder pressure in the engine.
Another challenge with a nitrous oxide system is getting the delivery of nitrous oxide and additional fuel at the correct proportions. If you feed nitrous to the engine without enough extra fuel, the lean air/nitrous to fuel mixture will mean the engine will suffer from exactly the same problems of that faced by forced induction methods. Namely: Detonation, combustion temperatures will skyrocket and catastrophic failure is certain to occur. If the proportion is such that too much fuel is delivered, the power advantage degrades rapidly.
As you can see, nitrous oxide is like any other power increasing modification in that, when used wisely and installed properly, it works well. When used foolishly or installed incorrectly it can significantly reduced the reliability and durability of your engine.
Nitrous oxide is also a great value on a Pound-per-unit-power increase when installed and operated properly. The downside, of course, is the fun ends quickly, very quickly. The power boost lasts as long as the nitrous. The average bottle is 20 pounds (Weight that is) and with a well tuned street V8 that might be worth 20 seconds of use.
So, nitrous oxide is not the instant-engine-failure many people think it is. When used properly and when dispensed by a properly designed and installed system nitrous oxide can be responsible for some phenomenal increases in power.