Nitrous oxide engine
The term NOS is derived from the initials of the company name Nitrous Oxide Systems, Inc. (now a brand of Holley Performance Products) one of the pioneering companies in the development of nitrous oxide injection systems for automotive performance use, and has become a genericized trademark.
This oxygen supports combustion; it combines with fuels such as gasoline, alcohol, diesel fuel, propane, or compressed natural gas (CNG) to produce carbon dioxide and water vapor, along with heat, which causes the former two products of combustion to expand and exert pressure on pistons, driving the engine.
As the decomposition of N2O into oxygen and nitrogen gas is exothermic and thus contributes to a higher temperature in the combustion engine, the decomposition increases engine efficiency and performance, which is directly related to the difference in temperature between the unburned fuel mixture and the hot combustion gasses produced in the cylinders.
Progressive systems have the advantage of utilizing a larger amount of nitrous (and fuel) to produce even greater power increases as the additional power and torque are gradually introduced (as opposed to being applied to the engine and transmission immediately), reducing the risk of mechanical shock and, consequently, damage.
Cars with nitrous-equipped engines may be identified by the "purge" of the delivery system that most drivers perform prior to reaching the starting line.
A separate electrically operated valve is used to release air and gaseous nitrous oxide trapped in the delivery system.
When the purge system is activated, one or more plumes of nitrous oxide will be visible for a moment as the liquid flashes to vapor as it is released.
Dry systems are not typically used in carbureted applications due to the nature of a carburetor's function and inability to provide large amounts of on-demand fuel.
In wet systems on fuel/direct injected engines care must be taken to avoid backfires caused by fuel pooling in the intake tract or manifold and/or uneven distribution of the nitrous/fuel mixture.
Being that direct port systems do not have to rely on intake tract/manifold design to evenly distribute the nitrous or fuel/nitrous mixture, they are inherently more precise than other delivery methods.
Proper strengthening of engine components in addition to accurate and adequate fuel delivery are key to nitrous system use without catastrophic failure.
For example, in New South Wales, Australia, the Roads & Traffic Authority Code of Practice for Light Vehicle Modifications (in use since 1994) states in clause 3.1.5.7.3 that The use or fitment of nitrous oxide injection systems is not permitted.
In Germany, despite its strict TÜV rules, a nitrous system can be installed and used legally in a street driven car.
It was sometimes used with the Luftwaffe's form of methanol-water injection, designated MW 50 (both meant as Notleistung short-term power boosting measures), to produce substantial increases in performance for fighter aircraft over short periods of time, as with their combined use on the Focke-Wulf Ta 152H fighter prototypes.
[3] British World War II usage of nitrous oxide injector systems were modifications of Merlin engines carried out by the Heston Aircraft Company for use in certain night fighter variants of the de Havilland Mosquito and photo reconnaissance versions of the Supermarine Spitfire.
