Nitrous



Nitrous is an often used abbreviation for the chemical compound nitrous oxide (N2O) also referred to as NOS. The term NOS is derived from the abbreviation of the company name Nitrous Oxide Systems (NOS), one of the pioneering companies in the development of nitrous oxide injection systems for automotive performance use. More recently, the term was used prominently in the film The Fast and the Furious, and not surprisingly, shortly after the film's release, various automotive newsgroups and forums featured unprecedented numbers of inquiries about "NOS" and how to install and use it. To a biochemist, however, NOS refers to nitric oxide synthase.

Nitrous oxide is an oxidizing agent used to increase an engine's power output by allowing more fuel (usually gasoline or alcohol) to be burned than would normally be the case.

Overview
When nitrous oxide decomposes, a single mole will release 1/2 mole of oxygen gas, allowing an oxygen saturation of 33% to be reached. Air, which contains only 21% oxygen, permits a maximum saturation of only 21%. This oxygen combines with hydrocarbons such as gasoline, alcohol, and diesel fuel to produce carbon dioxide and water vapor, which expand and exert pressure on pistons.

Nitrous oxide is stored as a liquid in tanks, but because of its low boiling point it vaporizes easily when released to atmosphere. When injected into an inlet manifold this characteristic causes a reduction in air/fuel charge temperature with an associated increase in density, thereby increasing the cylinder's volumetric efficiency.

When N2O breaks down in the engines combustion phase, the oxygen atoms are freed from their bond to the nitrogen atoms in an exothermic reaction, contributing to the overall power increase.

Nitrous systems can increase power by as little as 0.5 hp or as much as 3,000 hp, depending on the engine type and nitrous system type. All systems are based on a single power kits but these kits can be used in multiples (called 2, 3 or even 4 stage); 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 cars and some Pro Street cars use three stages for additional power, but more and more are switching to pulsed progressive technology.

Fans can easily identify nitrous-equipped cars at the track by the fact that most will "purge" the delivery system 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 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—air or gaseous nitrous oxide in the line will cause the car to "bog" for an instant until liquid nitrous oxide reaches the intake.

Types of nitrous systems
There are two main categories of nitrous systems: dry & wet. A nitrous system is primarily concerned with introducing fuel and nitrous into the engine's cylinders, and combining them for more efficient combustion. There are 4 main sub types of wet system: single point, direct port, plate, and plenum bar all of which are just slightly different methods of discharging nitrous into the plenums of the intake manifold.

Dry
In a dry nitrous system, extra fuel required is introduced through the fuel injectors, keeping the manifold dry of nitrous. This property is what gives the dry system its name. Fuel flow can be increased either by increasing the pressure in the fuel injection system, or by modifying the vehicle's computer to increase the time the fuel injectors remain open during the engine cycle. This is typically done by spraying nitrous past the mass airflow sensor (MAF), which then sends a signal to the vehicle's computer telling it that it sees colder denser air, and that more fuel is needed. This is typically not an exact method of adding fuel. Once additional fuel has been introduced, it can burn with the extra oxygen provided by the nitrous, providing additional power.

Dry nitrous systems rely on a single type nozzle that only sprays nitrous through it, not nitrous and fuel. These nitrous nozzles generally spray in a 90 degree pattern.

Wet single-point
A wet single-point nitrous system introduces the fuel and nitrous together, causing the upper intake to become wet with fuel. In carbureted applications, this is typically accomplished with a spraybar plate mounted between the carburetor base and the intake manifold, while cars fitted with electronic fuel injection often use a plate mounted between the manifold and the base of the throttle body, or a single nozzle mounted in the intake tract. However, most makes of nitrous systems combined with unsuitable intake designs, often result in distribution problems and/or intake backfires. Dry-flow intakes are designed to contain only air, which will travel through smaller pipes and tighter turns with less pressure, whereas wet-flow intakes are designed to contain a mixture of fuel and air. Wet nitrous systems tend to produce more power than dry systems, but in some cases can be more expensive and difficult to install.

A wet nozzle differs in the way that it takes in both nitrous and fuel which are metered by jets to create a perfect or proper air-fuel ratio (AFR).

Newer wet nitrous kits on domestic cars have become increasingly easy to install by pulling fuel via the schrader valve on the fuel rail which is normally designated as a fuel test port. It makes plumbing and using a wet nitrous kit much more simple.

Wet direct port
A wet direct port nitrous system introduces nitrous and fuel directly into each intake port on the engine. These systems are also known as direct port nitrous systems. Normally, these systems combine nitrous and fuel through several nozzles similar in design to a wet single-point nozzle, which mixes and meters the nitrous and fuel delivered to each cylinder individually, allowing each cylinder's nitrous/fuel ratio to be adjusted without affecting the other cylinders. Note that there are still several ways to introduce nitrous through a direct port system. There are several different types of nozzles and placements ranging from fogger nozzles that requires one to drill and tap the manifold, to specialty direct port E.F.I. nozzles that fit into the fuel injector ports along with the fuel injectors.

A multi-point system is the most powerful type of nitrous system, due to the placement of the nozzle in each runner, as well as the ability to use more and higher capacity solenoid valves. Wet multi-point kits can go as high as 3,000 horsepower (2,400 kW) with only one stage, but most produce less than half that amount with two, three or even four stages. These systems are also the most complex and expensive systems, requiring significant modification to the engine, including adding distribution blocks and solenoid assemblies, as well as drilling, tapping and constructing plumbing for each cylinder runner. These systems are most often used on racing vehicles specially built to take the strain of such high power levels. Many high-horsepower race applications will use more than one nozzle per cylinder, plumbed in stages to allow greater control of how much power is delivered with each stage. A two-stage system will actually allow three different levels of additional horsepower; for example, a small first stage can be used in first gear to prevent excessive wheelspin, then turned off in favor of a larger second stage once the car is moving. In top gear, both stages can be activated at the same time for maximum horsepower. A more recent improvement on the staged concept from WON is the progressive delivery system, which allows a simpler single stage system to act even better than multiple stages, delivering a smoothly progressive increase in power which is adjustable to suit the user requirements.

Plenum bar
Another type of system is called a plenum bar system. These are spraybars that are installed inside of the plenums of the intake manifold. Plenum bar systems are usually used in conjunction with direct port systems in multi-stage nitrous systems.

Reliability concerns


As all modifications to increase power, the use of nitrous oxide carries with it concerns about the reliability and longevity of an engine. Due to the greatly increased cylinder pressures, the engine as a whole is placed under greater stress, especially the parts involved with the combustion chamber. An engine with components not able 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, or crankshafts.

Even if the engine is up to the task, severe damage can occur if a problem occurs in the fuel system; an engine running with nitrous oxide depends heavily on the proper air to fuel ratio to prevent detonation from occurring. For example, if the engine's fuel supply was to be reduced, this would cause the engine to run lean by whatever degree the fuel delivery was reduced by which can lead to engine knock or detonation. Depending on the engine, this may only need to occur for a matter of seconds before major damage occurs.

Despite these concerns, most modern OEM engines can reliably handle a nitrous power increase in the region of 50%, especially when that power is delivered using progressive control.

Legality
Nitrous oxide injection systems for automobiles are usually emissions legal, but in most states it is illegal to have an open bottle valve on the street. Although some localities require certified system components. There have been reported instances of police officers arresting drivers of vehicles equipped with N2O injection systems on the grounds that he or she intends to inhale it, although such auto-grade N2O is often mixed with about 100 ppm sulfur dioxide, making inhalation noxious or even fatal.

Sanctioning bodies in motor sports have banned nitrous oxide use in some classes; in 1976, NASCAR disqualified many drivers for doing so;  in June 1998, the NHRA suspended Pro Stock driver Jerry Eckman and car owner Bill Orndorff for a year, stripped the team of all points, and imposed a fine for violations. The team closed down shortly after the suspension.

History
A similar basic technique was used during World War II by Luftwaffe aircraft with the GM 1 system to maintain the power output of aircraft engines when at high altitude where the oxygen content is lower. Accordingly, it was only used by specialized planes like high-altitude reconnaissance aircraft, high-speed bombers and high-altitude interceptors.

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 PR versions of the Supermarine Spitfire.