How does a nitro booster (NOS) or nitrous works?

Undoubtedly, there shall be just a few, who are oblivious to the magical red button that transforms your car into a supercar in a matter of seconds, popularly known as the nitro booster or NOS (commercial term for Nitrous Oxide Systems) or simply nitro. Hopefully this post will answer your query as to how does a nitro booster works?




Inquisitions regarding the high tech stuffs seen in the hollywood action movies riddles the minds of tech-buffs and novices alike and when it comes to the exciting world of the street racing cars, seen in the movies like the fast and furious, it makes you wonder how the technologies like nitro booster actually works ? or whether it works at all ?

You may even a get a less than legitimate answer about such esoteric stuff, when you ask your neighbourhood geek. What's worse is that sometimes it's wrongly portrayed in the movies just to link it with the storyline which may often result in conjectural anomalies in the interpretations of the actual functionality. Here, I've tried to explain it in two ways, for easier understanding.

Simple & short explanation :

NOS is essentially N2O or nitrous oxide, which delivers higher levels of oxygen to the engine to enhance the burning rate of the fuel, which results in higher power leading to higher speed. 

Secondly, the discharge of this high pressure gas cools down the intake(fuel+air mixture), improving it's power output.

A Chevy Impala modified for racing


Longer & detailed explanation :

consider an internal combustion engine's working :

FUEL+AIR → combustion products + power 

we know that the air contains around 21% of oxygen and actual combustion takes place between fuel (hydrocarbons) and oxygen. So the rest of the air , around 79% is neutral(mostly nitrogen) and does not takes part in the combustion reaction in a bigger way. 


The Nitrous oxide molecule looks like this:


At elevated temperatures (about 563 to 573K), Nitrous oxide or N2O splits up in the engine as:  N2O2N+O

This extra oxygen that is available for combustion, increases the amount of oxygen inside the engine cylinder to about 50% . The 30% increase in the oxygen content rapidly increases the combustion rate of the fuel and more fuel gushes in due to increased intake vacuum in the forthcoming cycles. Thus more fuel is entered into the cylinder simultaneously. This leads to more power output. Sometimes it may increase the power by 150%.

More fuel + More oxygen → more combustion products + MORE power

This more power leads to higher acceleration and top speed for the vehicle. 

A second mechanism of power boost comes from the fact that the Nitrous oxide is injected at high pressures at the intake manifold. This results in rapid expansion of the same thus it's temperature decreases, cooling the surrounding air too. 

{ from PV=nRT , when can prove that rapid expansion of volume results in a decrease in temperature}

This decrease in temperature, makes the intake charge denser and thus it further results in more mass of (Air+ Fuel) reaching the engine per unit time. Secondly, it cools the intake charge, increasing the thermal efficiency of the engine. This results in a further 5-8% increase in power output. 

It must be noted here that increased oxygen composition makes the combustion mixture leaner and may result in detonation or extreme heating of engine up to the point of melting. One way to fight this is remap the injection to a more retarded point and the other is that we need to increase the amount of fuel by introduction of extra fuel, which is supplied manually, by various mechanisms:

dry nitrous : extra fuel is supplied by reprogramming the fuel injector to eject more fuel into the intake

wet nitrous : contains a pre-mixed dose of fuel and the fuel+nitrous is simultaneously injected.

Pro or multi-port nitrous :  here, the nitrous+fuel is accurately metered and delivered directly into the intake of each of the engine cylinders separately. This is the most powerful booster and also the most efficient of all the nitrous boosters.

Drawbacks:

One main reason why we cannot use Nitrous for sustained periods of time is that the consumption rate of air of an engine per litre of fuel may be very high at high engine speeds thus the cylinder of NOS lasts at max for around a few minutes even though it is stored as highly compressed liquid in the cylinders and flow rates are kept under control. 

Another drawback is that the increased rate of combustion, puts huge amount of pressure on the cylinder walls and the piston, which may break prematurely under such conditions. To prevent such a thing from happening, generally NOS kits are fitted only on high-end engines,which are strong enough to sustain the extra loadings or some form of reinforcement is provided to the engine. 

Still another drawback is that the commercially available nitrous oxide is added with SO2 to prevent substance abuse (don't forget that Nitrous oxide is the 'laughing gas', which is also intoxicating/ anaesthetic). This sulphur dioxide may lead to acidic corrosion of the engine parts.

Arindra Mishra

A blogger, a photographer and an Engineer. I write about technology, engineering and photogrpahy.

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