A nitrous oxide engine, or nitrous oxide system (NOS) is an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

in which oxygen for burning the fuel comes from the decomposition of

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room te ...

, N₂O, as well as air. The system increases the engine's power output by allowing fuel to be burned at a higher-than-normal rate, because of the higher

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

of oxygen injected with the

fuel mixture A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...

. Nitrous injection systems may be "dry", where the nitrous oxide is injected separately from fuel, or "wet" in which additional fuel is carried into the engine along with the nitrous. NOS may not be permitted for street or highway use, depending on local regulations. N₂O use is permitted in certain classes of auto racing. Reliable operation of an engine with nitrous injection requires careful attention to the strength of engine components and to the accuracy of the mixing systems, otherwise destructive detonations or exceeding engineered component maximums may occur. Nitrous oxide systems were applied as early as World War II for certain aircraft engines.

Terminology

In the context of racing, nitrous oxide is often termed nitrous or NOS. The term NOS is derived from the initials of the company name Nitrous Oxide Systems, Inc. (now a brand of

Holley Performance Products Holley Performance Products is an automobile, automotive performance company based in Bowling Green, Kentucky. It was founded in 1896 in Bradford, Pennsylvania, by George Holley and Earl Holley. When the company was based in Michigan it was a majo ...

) one of the pioneering companies in the development of nitrous oxide injection systems for automotive performance use, and has become a

genericized trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...

. Nitro is also sometimes used, though incorrect, as it refers more to nitromethane engines.

Mechanism

When a

mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole" * Golden mole, southern African mammals * Marsupial mole Marsupial moles, the Notoryctidae family, are two species of highly specialized marsupial mammals that are found i ...

of nitrous oxide decomposes, it releases half a mole of O₂ molecules (oxygen gas), and one mole of N₂ molecules (nitrogen gas). This decomposition allows an oxygen concentration of 36.36% to be reached. Nitrogen gas is non-combustible and does not support combustion.

Air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

—which contains only 21% oxygen, the rest being nitrogen and other equally non-combustible and non-combustion-supporting gasses—permits a 12-percent-lower maximum-oxygen level than that of nitrous oxide. This oxygen supports combustion; it combines with fuels such as gasoline, alcohol,

diesel fuel Diesel fuel, also called diesel oil, heavy oil (historically) or simply diesel, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a re ...

propane Propane () is a three-carbon chain alkane with the molecular formula . It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum ref ...

, or

compressed natural gas Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of , usually in ...

(CNG) to produce

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and water vapor, along with heat, which causes the former two products of combustion to expand and exert pressure on pistons, driving the engine. Nitrous oxide is stored as a liquid in tanks, but is a gas under atmospheric conditions. When injected as a liquid into an inlet manifold, the vaporization and expansion causes a reduction in air/fuel charge temperature with an associated increase in density, thereby increasing the cylinder's

volumetric efficiency Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke (if the gases were at the reference condition for density) to th ...

. As the decomposition of N₂O into oxygen and nitrogen gas is

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

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. All systems are based on a single stage kit, but these kits can be used in multiples (called two-, three-, or even four-stage kits). The most advanced systems are controlled by an electronic progressive delivery unit that allows a single kit to perform better than multiple kits can. Most Pro Mod and some Pro Street drag race cars use three stages for additional power, but more and more are switching to pulsed progressive technology. 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.

Identification

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. This brings liquid nitrous oxide all the way up through the plumbing from the storage tank to the

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...

valve or valves that will release it into the engine's intake tract. 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. The purpose of a nitrous purge is to ensure that the correct amount of nitrous oxide is delivered the moment the system is activated as nitrous and fuel jets are sized to produce correct air / fuel ratios, and as liquid nitrous is denser than gaseous nitrous, any nitrous vapor in the lines will cause the car to "bog" for an instant (as the ratio of nitrous / fuel will be too rich reducing engine power) until liquid nitrous oxide reaches the injection nozzle.

Types of nitrous systems

There are two categories of nitrous systems: ''dry'' & ''wet'' with four main delivery methods of nitrous systems: ''single nozzle'', ''direct port'', ''plate'', and ''bar'' used to discharge nitrous into the plenums of the

intake manifold An inlet manifold or intake manifold (in American English) is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinder (engine), cylinders. The word ''manifold (engineering), manifold'' comes from the Old Eng ...

. Nearly all nitrous systems use specific orifice inserts, called jets, along with pressure calculations to meter the nitrous, or nitrous and fuel in wet applications, delivered to create a proper air-fuel ratio (AFR) for the additional horsepower desired.

Dry

In a ''dry'' nitrous system the nitrous delivery method provides nitrous only. The extra fuel required is introduced through the fuel injectors, keeping the manifold dry of fuel. This property is what gives the dry system its name. Fuel flow can be increased either by increasing the pressure or by increasing the time the fuel injectors remain open. Dry nitrous systems typically rely on a single nozzle delivery method, but all of the four main delivery methods can be used in dry applications. 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. Dry nitrous systems on fuel injected engines will use increased fuel pressure or injector pulsewidth upon system activation as a means of providing the correct ratio of fuel for the nitrous.

Wet

In a ''wet'' nitrous system the nitrous delivery method provides nitrous and fuel together resulting in the intake manifold being "wet" with fuel, giving the category its name. Wet nitrous systems can be used in all four main delivery methods. 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. Port and direct fuel injection engines have intake systems engineered for the delivery of air only, not air and fuel. Since most fuels are heavier than air and not in a gaseous state when used with nitrous systems it does not behave in the same way as air alone; thus the possibility of the fuel being unevenly distributed to the combustion chambers of the engine causing lean conditions/detonation and/or pooling in parts of the intake tract/manifold presenting a dangerous situation in which the fuel may be ignited uncontrollably causing catastrophic failure to components. Carbureted and single point/throttle body injected engines use a wet manifold design that is engineered to evenly distribute fuel and air mixtures to all combustion chambers, making this mostly a non-issue for these applications.

Single nozzle

A ''single nozzle'' nitrous system introduces the nitrous or fuel/nitrous mixture via a single injection point. The nozzle is typically placed in the intake pipe/tract after the air filter, prior to the intake manifold and/or throttle body in fuel injected applications, and after the throttle body in carbureted applications. In wet systems the high pressures of the nitrous injected causes the

aerosolization Aerosolization is the process or act of converting some physical substance into the form of particles small and light enough to be carried on the air i.e. into an aerosol. Aerosolization refers to a process of intentionally oxidatively converting a ...

of the fuel injected in tandem via the nozzle, allowing for more thorough and even distribution of the nitrous/fuel mixture.

Direct port

A ''direct port'' nitrous system introduces the nitrous or fuel/nitrous mixture as close to the intake ports of the engine as is feasible via individual nozzles directly in each intake runner. Direct port nitrous systems will use the same or similar nozzles as those in single nozzle systems, just in numbers equal to or in multiples of the number of intake ports of the engine. 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. The greater number of nozzles also allows a greater total amount of nitrous to be delivered than other systems. Multiple "stages" of nitrous can be accomplished by using multiple sets of nozzles at each intake port to further increase the power potential. Direct port nitrous systems are the most common delivery method in racing applications.

Plate

A ''plate'' nitrous system uses a spacer placed somewhere between the throttle body and intake ports with holes drilled along its interior surfaces, or in a tube that is suspended from the plate, for the nitrous or fuel/nitrous mixture to be distributed through. Plate systems provide a drill-less solution compared to other delivery methods as the plates are generally application specific and fit between existing components such as the throttle body-to-intake-manifold or upper-intake-manifold-to-lower-intake-manifold junctions. Requiring little more than longer fasteners, plate systems are the most easily reversed systems as they need little to no permanent changes to the intake tract. Dependent on application, plate systems can provide precise nitrous or fuel/nitrous mixture distribution similar to that of direct port systems.

Bar

A ''bar'' nitrous system utilizes a hollow tube, with a number of holes drilled along its length, placed inside the intake plenum to deliver nitrous. Bar nitrous delivery methods are almost exclusively dry nitrous systems due to the non-optimal fuel distribution possibilities of the bar. Bar nitrous systems are popular with racers that prefer their nitrous use to be hidden, as the nitrous distribution method is not immediately apparent and most associated components of the nitrous system can be obscured from view.

Propane or CNG

Nitrous systems can be used with a gaseous fuel such as propane or compressed natural gas. This has the advantage of being technically a ''dry'' system as the fuel is not in a liquid state when introduced to the intake tract.

Reliability concerns

The use of nitrous oxide carries with it concerns about the reliability and longevity of an engine present with all power adders. Due to the greatly increased cylinder pressures, the engine as a whole is placed under greater stress, primarily those components associated with the engine's rotating assembly. An engine with components unable to cope with the increased stress imposed by the use of nitrous systems can experience major engine damage, such as cracked or destroyed pistons, connecting rods, crankshafts, and/or blocks. Proper strengthening of engine components in addition to accurate and adequate fuel delivery are key to nitrous system use without catastrophic failure. In addition, nitrous oxide should not be used in vehicles with an

automatic transmission An automatic transmission (AT) or automatic gearbox is a multi-speed transmission (mechanics), transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions. The 1904 ...

, as the highly increased engine power and torque may cause stress damage to the

torque converter A torque converter is a device, usually implemented as a type of fluid coupling, that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automatic transmission, the ...

and the transmission itself.

Street legality

Nitrous oxide injection systems for automobiles are illegal for road use in some countries. For example, in

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, Australia, the

Roads & Traffic Authority The Roads & Traffic Authority (RTA) was an Statutory authority, agency of the Government of New South Wales responsible for major road infrastructure, licensing of drivers, and registration of motor vehicles. The RTA directly managed state ...

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 Great Britain, there are no restrictions on the use of , but the modification must be declared to the insurance company, which is likely to result in a higher premium or refusal to insure. In Germany, despite its strict TÜV rules, a nitrous system can be installed and used legally in a street driven car. The requirements for the technical standard of the system are similar to those of aftermarket natural gas conversions.

Racing rules

Several sanctioning bodies in drag racing allow or disallow the use of nitrous oxide in certain classes or have nitrous oxide specific classes. Nitrous is allowed in

Formula Drift Formula DRIFT (also known as Formula D or FD) is an American drifting series, and was co-founded by Jim Liaw and Ryan Sage in 2003 as a sister company to Slipstream Global Marketing, the same partnership that introduced D1 Grand Prix to the ...

competition.

History

A similar basic technique was used during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

Luftwaffe The Luftwaffe () was the aerial warfare, aerial-warfare branch of the before and during World War II. German Empire, Germany's military air arms during World War I, the of the Imperial German Army, Imperial Army and the of the Imperial Ge ...

aircraft with the GM-1 system to maintain the power output of

aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...

s when at high altitude where the air density is lower. Accordingly, it was only used by specialized planes like high-altitude reconnaissance aircraft, high-speed bombers and high-altitude interceptors. 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. 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 The de Havilland DH.98 Mosquito is a British twin-engined, multirole combat aircraft, introduced during the World War II, Second World War. Unusual in that its airframe was constructed mostly of wood, it was nicknamed the "Wooden Wonder", or " ...

and photo reconnaissance versions of the

Supermarine Spitfire The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and other Allies of World War II, Allied countries before, during, and after World War II. It was the only British fighter produced conti ...

References

{{Reflist

External links

Howstuffworks "How does nitrous oxide help an engine perform better?"
Vehicle modifications Engine technology Gas technologies