In vehicle
racing, nitrous oxide (often referred to as just "
nitrous" or as NOS after the name of the brand
Nitrous Oxide Systems) allows the engine to burn more fuel and air, resulting in a more powerful combustion. The gas itself is not flammable, but it delivers more
oxygen than atmospheric air by breaking down at elevated temperatures.
Nitrous oxide is stored as a compressed liquid; the
evaporation and expansion of liquid nitrous oxide in the
intake manifold causes a large drop in intake charge temperature, resulting in a denser charge, further allowing more air/fuel mixture to enter the cylinder. Nitrous oxide is sometimes injected into (or prior to) the intake manifold, whereas other systems directly inject right before the cylinder (direct port injection) to increase power.
The technique was used during
World War II by
Luftwaffe aircraft with the
GM-1 system to boost the power output of
aircraft engines. Originally meant to provide the
Luftwaffe standard aircraft with superior high-altitude performance, technological considerations limited its use to extremely high altitudes. Accordingly, it was only used by specialized planes like high-altitude
reconnaissance aircraft,
high-speed bombers, and high-altitude
interceptor aircraft.
One of the major problems of using nitrous oxide in a reciprocating engine is that it can produce enough power to damage or destroy the engine. Very large power increases are possible, and if the mechanical structure of the engine is not properly reinforced, the engine may be severely damaged or destroyed during this kind of operation. It is very important with nitrous oxide augmentation of
internal combustion engines to maintain proper
operating temperatures and fuel levels to prevent "preignition", or "detonation" (sometimes referred to as "knocking" or "pinging"). Most problems that are associated with nitrous do not come from mechanical failure due to the power increases. Since nitrous allows a much denser charge into the cylinder it dramatically increases cylinder pressures. The increased pressure results in heat, and heat will cause many problems from melting the piston, valves or warping the head/cracking or predetonation.