What’s the Deal with NOS and How Does It Actually Work in Cars and Humans?

As far as successful film franchises go, few are as balls-to-the-wall insane as The Fast and the Furious. Best described as Mission: Impossible soaked in Axe Body Spray, the series is set in an alternate universe where few problems can’t be solved by driving muscle cars at it. Over its ten installments, the franchise has seen its band – sorry, family – of street racers-turned-international-crime-fighters drag bank vaults through the streets of Rio, race a Russian submarine across polar ice, and even fly a rocket-powered Pontiac Fiero into outer space, because sure, why not? Strange to think, then, that the whole saga began all the way back in 2001 with a low-budget Point Break ripoff about illegal street racers robbing DVD players off the back of trucks. But humble as it was compared to what came later, the first film established the cinematic language of drag racing that would become a staple for the series: the steely gazes of the two opponents as they pull up to the line. The scantily-clad woman dropping her arms to kick off the race. Tight, rapidly-edited shots of gear shifting. Close-ups of the NOS button being pressed and the exhaust pipe belching blue flame as the cars accelerate to seemingly supersonic speeds. If these films are your only reference point for auto racing, you have probably wondered: what is NOS – AKA Nitrous Oxide – anyway? How does it boost a car’s performance, and is it really the automotive warp drive that Vin Diesel and family would have you believe? Well, throw on your tank top and silver crucifix necklace as we dive into the high-octane science and history of nitrous oxide.

The discovery of Nitrous Oxide – chemical formula N₂O – is typically credited to English theologian and chemist Joseph Priestley. In 1767, Priestley moved to Leeds, where he lived next door to the local brewery. He soon became fascinated with the gases or “airs” produced by the fermentation vats, and embarked on a series of detailed experiments to study these mysterious substances. In the course of these investigations, Priestley discovered that the gas given off by the vats was “fixed air” – AKA carbon dioxide – and figured out how to dissolve this substance in water. This discovery, published in 1772, led directly to the establishment of the highly-lucrative carbonated water and later soft drink industry. In another experiment, Priestley heated iron filings soaked in nitric acid to produce a new gas that made flames burn brighter but was unbreathable by mice and other animals. He called this substance “dephlogisticated nitrous air”, in reference to the now-defunct phlogiston theory first proposed by German alchemist Johan Becher in 1667. This theory held that combustible materials contained a fire-like element called phlogiston that was released by burning and absorbed by the surrounding air. Once all the phlogiston was released and the air saturated, combustion stopped and could not be supported until the air was dephlogisticated. Today, of course, we know that dephlogisticated air is in fact the element oxygen, which is absorbed by burning substances and converted into carbon dioxide and other combustion products. This continues until the oxygen in the atmosphere is depleted and combustion stops, with the resulting “phlogisticated air” actually being a mixture of carbon dioxide, carbon monoxide and other combustion products as well as nitrogen and other inert gases from the air.

But while Priestley is traditionally credited with discovering nitrous oxide, it is now believed that he was beaten by over a decade by Scottish chemist Joseph Black, who in 1766 produced the gas by heating ammonium nitrate – the same process used today. Similarly, Priestley’s claim to have discovered oxygen is now typically credited to Swedish chemist Carl Wilhelm Scheele – though Priestley published his findings first.

Whatever the case, for nearly three decades Nitrous Oxide remained little more than a scientific footnote, until the great English chemist Sir Humphrey Davy – then working as a surgeon’s apprentice – began investigating the substance in the 1890s. To his astonishment and delight, Davy discovered that nitrous oxide, when inhaled, induced a powerful sense of euphoria and uncontrollable giggling. He had discovered laughing gas. Ever the consummate scientist, Davy had his close friends and had them record their experiences. J.W. Tobin reported that:

“When the [bladders of nitrous oxide] were exhausted and taken from me, I continued breathing with the same violence, then suddenly starting from the chair, and vociferating with pleasure, I made towards those that were present, as I wished they should participate in my feeling. I struck gently at Mr. Davy and a stranger entering the room at the moment, I made towards him, and gave him several blows, but more in the spirit of good humor than of anger. I then ran through different rooms of the house, and at last returned to the laboratory somewhat more composed; my spirits continued much elevated for some hours after the experiment…”

While poet Samuel Taylor Coleridge, author of The Rime of the Ancient Mariner, wrote:

“Then I first inspired the nitrous oxide, I felt a highly pleasurable sensation of warmth over my whole frame, resembling that which I remember once to have experienced after returning from a walk in the snow into a warm room. The only motion which I felt inclined to make, was that of laughing at those who were looking at me.”

Davy published his results in an 1800 with the unwieldy title of Researches, Chemical and Philosophical; Chiefly Concerning Nitrous Oxide or Dephlogisticated Nitrous Air, and its Respiration. Soon after, laughing gas parties became all the rage among the upper classes, with revellers inhaling the gas from pigs’ bladders and stumbling about for their own – and each others’ – amusement. One of these parties, held in Hartford, Connecticut in 1844, became the site of a discovery that forever changes the history of medicine. One of the attendees, dentist Horace Wells, witnessed one reveller gash open his leg yet carry on partying as if he had felt nothing. Indeed, Humphry Davy had noted the painkilling effects of nitrous oxide forty years earlier, even using it during a wisdom tooth extraction, but did not pursue this discovery. The day after the party, Wells experimented on himself by inhaling nitrous oxide and having fellow dentist John Riggs extract one of his teeth. The experiment was a success, with Wells excitedly declaring:

“It is the greatest discovery ever made! I didn’t feel as much as the prick of a pin!”

Wells proceeded to test the procedure on 12 patients, with equally positive results. As Hartford did not have a hospital, Wells arranged to give a public demonstration at the Massachusetts General Hospital in Boston, which took place on January 20, 1845. Surrounded by an audience of doctors, Wells administered nitrous oxide to his patient and proceeded to extract a tooth – only for the patient to cry out in pain. The audience immediately broke out into boos and cries of “humbug!” forcing Wells to slink out in disgrace. It was later determined that the gas had been improperly administered, and that the patient’s obesity and alcoholism had made his body insensitive to the anaesthetic. Furthermore, despite having cried out, the patient did not recall feeling any pain. Sadly, however, the botched demonstration effectively ended Wells’s career. He soon fell ill, closed his dental practice, became addicted to ether and chloroform, and was imprisoned on January 21, 1848 for throwing sulphuric acid on two prostitutes in a drug-fuelled rage. Three days later, aghast at what he had done, he committed suicide in his cell.

But this was not the end of the story, for present at Wells’s 1845 demonstration was fellow dentist and former colleague William Morton. Convinced that nitrous oxide was an unreliable surgical anaesthetic, on October 16, 1846 Morton made medical history by removing a tumour from the neck of printer Edward Gilbert after knocking him out using diethyl ether. The landmark surgery took place in the same theatre as Wells’s ill-fated demonstration, which today is commonly known as the “Ether Dome.” Ether, along with chloroform, quickly became the surgical anaesthetic of choice, allowing ever longer and more complex surgeries to be performed without the patient thrashing about in agony. But while these were eventually replaced by safer and more effective general anaesthetics like desflurane and sevoflurane, nitrous oxide continues to be used to this day, primarily in dentistry and obstetrics. In these applications the gas is usually diluted to 30-40% with oxygen, as nitrous oxide cannot be breathed in pure form without asphyxiating the patient. Ironically, the use of nitrous oxide was popularized after Horace Wells’s death by Gardner Colton, host of the laughing gas party where Wells made his fateful observation.

For nearly a century and a half after its discovery, nitrous oxide had few applications outside of medicine and as a recreational drug. In 1949, however, Austrian engineer Eduard Haas discovered how to use laughing gas to produce another joy-inducing substance: whipped cream. When stored in a pressurized container, nitrous oxide, which is lipophilic or fat-binding, dissolves in cream; it also inhibits bacterial growth, extending the life of the mixture. When the pressure is released, however, the gas comes out of solution and froths the cream, creating that oh-so-delicious confection we all love to squirt directly into our mouths – er, I mean, spray onto desserts in reasonable amounts. While consumer whipped cream cans come pre-charged and are single-use, commercial refillable whipped cream dispensers use pre-charged nitrous oxide cartridges commonly known as chargers or ‘whippits.’ Unfortunately, however, the ready availability and legality of whippits makes them a popular source of nitrous oxide for recreational users, who consume the gas by breaking the seal on the charger with a special tool called a cracker and dispensing it into a balloon. Inhaling directly from the charger is dangerous, as the expanding gas is extremely cold and can inflict severe frostbite to the user’s mouth and respiratory tract. While nitrous oxide’s mechanism of action is not fully understood, it is believed that, like benzodiazepine drugs and opiates like morphine, the molecule binds to Gamma-Aminobutyric Acid or GABA and endogenous opioid receptors in the brain. This is evidenced by the fact that addicts who develop a tolerance to these drugs also develop a tolerance to nitrous oxide – and vice versa. Long-term nitrous oxide abuse can also lead to addiction, as well as severe vitamin B12 deficiency and associated neurological damage. This means that Devo was wrong: if a problem comes along, you must not whip it.

And finally, we get to the most dramatic use of nitrous oxide: making things go vroom. The first nitrous oxide injection system for internal combustion engines was developed by the Germans during the Second World War. Known as Göring Mischung Eins or “Göring Mixture 1” after head of the Luftwaffe Hermann Göring – but nicknamed the Ha-Ha-Gerät or “Ha Ha Device” – the system was invented in 1940 by engineer Otto Lutz to solve a serious problem plaguing high-altitude German bombers and fighters. As aircraft flew higher, the air grew progressively thinner, making it harder to supply the engine with oxygen and causing performance to drop rapidly. The traditional solution to this problem was to fit the engine with a supercharger or turbocharger, high-speed pumps which can compress and feed more air into the engine than natural induction alone. However, Germany lacked the metallurgical experience and production capacity to build these devices in sufficient numbers. GM-1 was a practical workaround that allowed engine performance to be boosted at high altitudes – at least for brief periods. The system worked in two ways. First, when nitrous oxide is heated above 300ºC, it decomposes into nitrogen and oxygen. This mixture contains 37% oxygen by mass compared to only 21% for regular air, meaning more fuel could be fed into the engine and more power obtained. Injecting nitrous oxide into the intake manifold also cooled the air, increasing its density and allowing even more oxygen to be fed into the cylinders. Finally the decomposition of nitrous oxide is exothermic, increasing the temperature inside the cylinders and improving the thermodynamic efficiency of the engine.

GM-1 was often used in tandem with another system called MW 50, which injected a 50:50 mixture of water and methanol into the intake manifold. As well as increasing the density of the inducted air, this mixture cooled the cylinders and helped prevent pre-detonation or knocking – the premature ignition of the fuel-air mixture caused by compression from the pistons. This, in turn, allowed the engine to achieve higher compression ratios and produce more power – and to learn more about engine knocking and how it affects what kind of fuel you put in your car, please check out our previous video What Does the “Octane Rating” of Fuel Really Mean? And in case you are wondering, the methanol in the mixture was to prevent the water from freezing at high altitudes.

Together, GM-1 and MW 50 could boost an engine’s performance by up to 500 horsepower and allow aircraft to operate at altitudes up to 20,000 feet – especially if used in tandem with a supercharger. Indeed, one of the few aircraft to have both systems fitted, the Focke-Wulf Ta 152 interceptor, was capable of reaching speeds of up to 756 kilometres per hour. But this blistering performance came at a price. For one thing, these systems were very heavy and bulky, reducing the aircraft’s performance and taking up weight and space that could otherwise be used for extra fuel and ordnance. They were also very thirsty, with the average aircraft only carrying enough water and nitrous oxide for around 10 minutes of continuous operation at full power. Pilots thus only used engine boost for brief periods such as the final climb before interception or when taking evasive action. However, by the time these systems were introduced in large numbers, Germany had already lost air superiority over Europe and high-altitude missions had become less relevant, meaning they were seldom used before the war ended. Meanwhile, the Allies also made limited use of nitrous oxide and water injection systems, especially in high-altitude reconnaissance aircraft.

With the rise of jet-powered aircraft after the Second World War, nitrous oxide injection became obsolete and passed into the annals of military aviation. It would be nearly two decades before the technology was rediscovered by a pioneer of the fledgling sport of high performance drag racing. In 1958, drag racer Richard Flynn of Spokane, Washington was combing his local library for potential high-energy fuels to feed into his next vehicle. Flynn had previously tried injecting pure oxygen into his engine, but this made the fuel-air-mixture dangerously unstable – a fact he discovered when his dragster proceeded to undergo a rapid unscheduled disassembly. In the course of his research, Flynn stumbled upon the wartime technique of nitrous oxide injection, which he realized could produce the desired performance boost without the risk of catastrophic explosions. It was also much more convenient to handle. At room temperature, gaseous oxygen can only be practically compressed up to a density of 279 kilograms per cubic metre at a pressure of 20 megapascals; to achieve greater density, it must be liquefied at temperatures below -196ºC, requiring impractically cumbersome cryogenic equipment. Nitrous oxide, by contrast, liquefies to a density of 800 kilograms per cubic metre above 4 megapascals at room temperature, meaning larger amounts can be carried using much simpler equipment. Flynn brought the idea to fellow drag racer Gary Hams, who proceeded to cobble together the world’s first automotive nitrous oxide system from a spare oxygen tank and regulator mounted in his car’s tool tray, a shop air hose and blowgun valve held in the driver’s lap, and a nozzle fixed to the base of the carburetor. On September 7, 1958, Hams entered his modified dragster in the B/Gas competition at Deer Park speedway, Minnesota, and handily won the race. This was, as far as it is known, the first-ever use of nitrous oxide in auto racing. Such boosted vehicles soon came to be known as “funny cars” after the famous psychotropic effects of nitrous oxide – though you shouldn’t try to breathe automotive nitrous as it is usually mixed with sulphur dioxide, corrosion inhibitors, and other highly-toxic substances. Don’t say we didn’t warn you…

From these humble beginnings, nitrous oxide boosting steadily grew in popularity among the racing community, and enterprising hobbyists began producing and selling ready-made kits for their fellow gear heads. Among the first such enterprises to find widespread success was 10,000 RPM Speed Equipment, founded in 1964 by Ron Hammel. In 1978, another racing enthusiast, Mike Thermos, was inspired by Hammel’s products to create his own line of nitrous oxide kits. Together with Dale Vaznaian, Thermos not only ironed out the various technical problems plaguing earlier systems, but also placed greater emphasis on aesthetics to better appeal to professional racers:

“We’d skin pack the kit. A lot of the guys were starting to do this stuff out of the back of their garage. But we painted ours, had our bottles painted really nice, put chrome valves on them — really gingerbread everything up.”

But what to call their new company? As Thermos later recalled:

“We had a buddy that painted the race cars. I asked if he can make us a logo? And he drew N-O-E  for Nitrous Oxide Engineering. I said, well, we’re not engineers so do something else. So he drew N-O-S like that. I said, yeah, that kind of looks like the symbol for nitrous oxide. We became Nitrous Oxide Systems.”

Nitrous Oxide Systems or NOS would go on to become legendary within the racing community – so much so that “NOS” has become a common slang term for nitrous oxide. By the time the company was sold to Holley Performance Products in 2001, it was valued at more than $5 million.

But as with all such technologies, it wasn’t long before racers began abusing nitrous oxide systems – even in NASCAR, where such performance-boosting methods are outlawed. This problem came to a head in February 1976 at the qualifying stage for the Daytona 500, when the No. 28 Hoss Ellington Chevrolet driven by A.J. Foyt and the No.88 DiGard Racing Chevy driven by Darrel Waltrip mysteriously clocked times one second faster than during practice laps. Suspecting foul play, NASCAR officials ordered Waltrip’s car to the inspection area, where they informed Waltrip and his crew chief Mario Rossi that they would cut the vehicle into little pieces until they found the nitrous oxide they were obviously using. Rossi caved and revealed the system hidden inside a chassis tube. Caught red-handed, Waltrip uttered an iconic line which underscored how ludicrously high the stakes had become in professional motorsports:

“If you don’t cheat, you look like an idiot. If you cheat and don’t get caught, you look like a hero. If you cheat and get caught, you look like a dope. Put me where I belong.”

Today, nitrous oxide systems are produced by dozens of companies in dozens of configurations tailored to particular vehicles or racing styles. However, broadly speaking there are only two main types of systems: dry and wet. Dry systems are the simplest, comprising one or more nozzles or jets mounted in the engine intake plenum. The liquid nitrous oxide fully vaporizes before entering the cylinders, hence the name. Operating such systems requires increasing the fuel flow to the engine to avoid an overly-lean condition, which can generate dangerously high temperatures and potentially damage the pistons and cylinders. This is accomplished by increasing the fuel pressure using a secondary pump or adjusting the electronic control module or ECU to keep the fuel injectors open for longer.

In wet systems, by contrast, liquid nitrous oxide and fuel are mixed together and delivered simultaneously into the carburetor or fuel injectors. While such systems do make it easier to control the fuel/air ratio, they can also suffer from uneven fuel distribution, fuel pooling, and lean conditions, potentially leading to detonations and other catastrophic damage. Meanwhile, dry systems can be used with one of four standard delivery methods: single nozzle, in which one jet is placed at the opening of the intake plenum; direct port, in which multiple jets are mounted close to the engine intake ports above the cylinders, plate, in which a flat spacer drilled with holes is mounted in the intake plenum to vaporize and distribute the nitrous, and bar, which is similar to a plate system but uses a hollow tube drilled with holes to distribute the nitrous. And while most nitrous oxide kits are based on a single delivery stage, multiple kits can be chained together to form multi-stage systems that deliver nitrous more progressively to ensure smoother acceleration. Different jet sizes can also be installed to tweak the oxidizer-fuel ratio.

But while nitrous oxide is most famous for boosting race cars, perhaps its most dramatic application is boosting payloads into space. On October 4, 2004, pilot Brian Binnie flew the experimental Scaled Composites SpaceShipOne to an altitude of 112 kilometres above the Mojave Desert – crossing the 100km Karman Line that marks the boundary of outer space. This flight, the second conducted in a week, won Scaled Composites the $10 Million Ansari X-Prize and officially made SpaceShipOne the first private craft to reach outer space – and for more on this, please check out our previous video The Surprisingly Interesting Debate of Where Outer Space Actually Begins.

Propelling SpaceShipOne on its record-breaking flights was an unusual type of power plant known as a hybrid rocket engine – which, as the name suggests, lies halfway in design between a traditional liquid rocket engine and solid rocket booster. The fuel in a hybrid rocket engine takes the form of a long cylinder or grain of hydrocarbon material – in the case of SpaceShipOne, a synthetic rubber called HTPB – with a hollow channel or port running down the middle. This is contained in a cylindrical combustion chamber with a rocket nozzle at one end and a tank of liquid or gaseous oxidizer at the other – in this case, our good old friend nitrous oxide. To start the engine, the pilot opens a valve to release the oxidizer into the fuel grain port and sets off a pyrotechnic charge to ignite the fuel. The fuel and oxidizer mix and burn in a narrow boundary layer along the inner surface of the fuel port, with the fuel grain being consumed from the inside out.

Hybrid rocket engines have numerous advantages over traditional liquid-fuelled engines and solid motors, particularly in the areas of safety and simplicity. Solid rocket motors combine fuel and oxidizer in same propellant grain, meaning that once they are ignited, they cannot be put out. Liquid-fuelled engines, meanwhile, often use toxic, volatile, and difficult to handle propellants like liquid oxygen or hydrazine, and are prone to exploding violently when they fail. They also require complex and difficult to manufacture hardware like propellant turbo pumps, making them very expensive. By contrast, the fuel and oxidizer used in hybrid engines are, on their own, largely inert and can be safely handled without special equipment. They are also considerably cheaper than traditional rocket fuels. Furthermore, hybrid rocket engines can easily and safely be shut off by simply cutting off the flow of oxidizer to the combustion chamber. On the other hand, hybrid rockets generally exhibit poorer performance and efficiency compared to liquid-fuelled rockets and suffer from a constantly-changing oxidizer-fuel ratio as the solid fuel grain is consumed. Their use thus involves tradeoffs between performance, cost, and safety.

Nor are hybrid rocket engines 100% safe. Though largely inert and safe to handle, nitrous oxide can still violently decompose if heated or exposed to the right catalyst. This lurking danger was tragically revealed on July 26, 2007 during a test of the engine for SpaceShipTwo, the rocket plane developed for space tourism firm Virgin Galactic. This was what is known as a cold flow test, and simply involved running nitrous oxide through the engine without igniting it to ensure that the blooming worked. Nonetheless, the nitrous oxide spontaneously decomposed, resulting in a massive explosion that killed three Scaled Composites engineers. While the cause of the explosion remains a mystery, it is known that turbulence can cause nitrous oxide to decompose at high flow rates. Hopefully the cause will be determined and the danger mitigated before Virgin Galactic begins commercial space tourism operations…

And that, dear viewers, is the surprisingly fascinating history of nitrous oxide, the unassuming molecule responsible for gifting humanity such indispensable scientific wonders as medical anaesthesia, billionaires in space, whipped cream, and hour-long YouTube supercuts of Vin Diesel saying “family”.

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