The capabilities of military aircraft, during World War II, escalated at a stratospheric rate as engineers battled to gain an advantage over the enemy.
Countless new technologies were developed, deployed and tested in combat as each nation sought to secure the upper hand in the skies. Faster, more nimble aircraft had an edge in close combat; bombers capable of cruising at greater altitudes were harder to intercept; night fighters guided by radar could hunt and shoot down unsuspecting invaders with ease.
Improving an aircraft's performance at higher altitudes proved problematic, however. As an aircraft climbed, the air around it would grow thinner. This less dense air also contained less oxygen - which the engine needed to effectively burn the fuel in its combustion chambers.
As the altitude of the aircraft increased, and the air density decreased, the power output of the engine would tail off. An increasingly sluggish, weak engine would doom a fighter facing an aircraft happier at higher altitudes, or make it nigh-on impossible to successfully interdict a high-flying multi-engined bomber.
Fortunately, a solution was available in the form of forced induction. Using a supercharger or turbocharger, or various combinations of both, would increase the pressure - and thus the density - of the air being fed into the engine. More oxygen would consequently be available in the cylinders, delivering improved performance at higher altitudes.
American fighters frequently demonstrated an advantage over their Axis counterparts at height. This was often down to their use compound turbocharger and supercharger setups, which delivered better high-altitude performance than many supercharged German engines. The German manufacturers, however, lacked the nickel required for alloys to build turbochargers in reliable, useful numbers. This similarly caused problems for various jet engine projects.
Professor Otto Lutz, working at the Institute of Engine Research, spotted a workaround. His work covered countless topics but one key focus was on that of rocket engines. These didn't rely on atmospheric air for combustion and instead used chemical oxidisers, releasing oxygen as they decomposed during combustion, which could be burnt with the rocket's fuel.
This, he concluded, could be used to a similar extent in piston engines. Many oxidisers were not suited to this application, however. Some were difficult to handle or store, while others were so volatile as to result in prompt engine self-disassembly if injected into a combustion chamber.
There was one non-toxic, stable oxidiser that had proven its worth in rocketry, though - nitrous oxide. It was also ideal, it transpired, for introducing extra oxygen into the combustion chamber of a piston engine; it released its oxygen in a progressive fashion as it was heated, helping keep conditions in the cylinder manageable, for starters. This extra oxygen could then be used to burn additional fuel, producing more power.
When injected as a liquid, the state change that took place as the nitrous changed to a gas also resulted in significant drops in temperature. This helped suppress detonation, keeping the engine in its preferable internal combustion configuration, and boosted output by increasing the density of the incoming charge.
It wasn't all good news, mind. Using nitrous required that the aircraft carry both a tank of oxidiser and a system to control its flow into the engine, resulting in a weight penalty. The operation of the system was also limited by the amount of oxidiser that could be carried. However, the extra performance would prove useful in an emergency situation and short bursts of additional power could allow the aircraft to get into an advantageous position.
The resulting first documented production system, introduced in 1940, was called the 'Göring Mischung 1' - 'Going Mixture 1'. Colloquially, because nitrous oxide was commonly known as laughing gas, many dubbed the system 'Ha-ha Gerät' - the 'Ha-Ha Device'.
It was first employed in the Bf 109E, in the E-7/NZ and E-7/Z variants, in August 1940. Unassisted, the 109's 33.9-litre Daimler-Benz 601N, an inverted, direct-injected and supercharged V12, punched out 1175hp from ground level to 16,000 feet. Set to its maximum output, the nitrous could ramp up the output of the big V12 by some 25 per cent - and help maintain higher power outputs at higher altitudes.
The system could be adapted to myriad applications too; it saw service in the Focke-Wulf Fw 190, boosting power from some 1825hp to in excess of 2230hp. The high-flying diesel Junkers Ju-86P made use of GM-1 as well, using it to climb away from interceptors.
Several factors, including the system's weight penalty, led to GM-1 being sidelined prior to the end of the war. The Germans weren't the only to employ nitrous, however; a limited number of Spitfires and Mosquitos were equipped with nitrous oxide injection. The Mosquito, for example, gained 250hp per Merlin on nitrous, resulting in a 30mph speed increase above 18,000 feet.
According to reports at the time, the US Air Force was less interested in nitrous oxide injection - as it reputedly considered the risk of terminal engine failure to far outweigh the often short-lived benefits.
For example, The National Advisory Committee for Aeronautics' wartime report from June 1945 stated that "the increase in cylinder head temperature was considerably greater for a given increase in power output with nitrous oxide supercharging than with air supercharging."
More prominently, the invention and rapid development of the jet engine negated the need to pursue power-adding methods for piston engines - which were becoming more powerful, at any rate, thanks to improved supercharging, turbocharging and engine management systems.
As a result, nitrous oxide injection slipped quietly into the history books. Following the war, however, as the hot rod and racing scene exploded in the United States, racers began to seek out anything that could grant them a potential advantage on the strip. Archives, libraries and reports were trawled to find the next magic bullet to knock a tenth off a standing quarter.
According to Hot Rod magazine, it was drag racer Dick Flynn who first exploited nitrous oxide in an automotive application, in 1958. He had witnessed other teams attempting to inject pure oxygen, which simply led to unsurprisingly catastrophic failures, and his research led him to the more stable nitrous oxide.
Myriad trials and tribulations led the system to become reliable and effective, unleashing additional power - in conjunction with extra fuel - at the press of a button. Others took note and formed companies to supply kits.
It wasn't until 1978, however, that the first perfected set-up was marketed by newcomer Nitrous Oxide Systems. The company and its kits rose to fame and continued to thrive, and was eventually bought out by Holley Performance Products in 1999 - two years before the brand became a household name after being thrown into the limelight in 2001's 'The Fast and the Furious'.
There was even a tentative effort made by MG, in the XPower SV, to introduce a production car fitted with nitrous oxide. It was merely mooted, however, and seemingly no cars were ever so equipped. Consequently, the use of nitrous oxide injection remains strictly in the domain of the aftermarket, with several companies - including Edelbrock, Wizards of Nitrous, Nitrous Express and Zex - offering systems for tuners and racers.
Like the systems of old, these 'throttle in a bottle' kits deliver a useful edge - albeit a short-lived one. But, as was the case in its original application during World War II, that momentary advantage is often all that's required.
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