If you have watched the first installment of the Fast and Furious franchise or any street car races, chances are you have heard about a compound termed NOS which appears to boost the speed of automobiles.
Nitrous oxide compound, aka NOS (Nitrous Oxide System), causes a surge in the engine's power and torque, at least from what we've seen in Hollywood.
Have you ever wondered how this happens? Well, you came to the right place. The big question, of course, is how Nitro Boost works and how the engine generates this surge in power.
First, we have to understand the combustion process in the engine of a car. The engine generates power as a result of the combustion of fuel and air.
Air is a compound consisting of various gas elements in different compositions, with 78% comprising of nitrogen and oxygen making up 21%. However, nitrogen gas is not involved in the combustion process because it is noncombustible.
So, what role does nitrous oxide play in an engine?
Since combustion utilizes oxygen, it follows that increasing oxygen and fuel in the engine would generate more power. It is at this point where nitrous oxide comes in. It provides the engine with an extra amount of oxygen which, in turn, increases the power output.
Nitrous oxide, therefore, works just the same way as sodium chlorate. You can think of nitrous oxide as an oxidizer propellant. With the application of heat to nitrous oxide, it decomposes and releases the individual elements in it.
If injected into the engine system, nitrous oxide will break down into oxygen and nitrogen upon heat application. Combustion of the extra oxygen produced and more fuel generates more power.
Of course, the whole nitrous oxide idea has a flaw. Nitrous oxide is bulky and to get a substantial boost in power, a lot of it is required.
However, you can't keep the car running on nitrous oxide. A large amount of it is needed which is not realistically achievable. For this reason, cars usually have a few minutes of nitrous oxide injection, and it is fired selectively when necessary.
Nitro boost is a concept that has been around for a while as early as during World War II. Some aircrafts had nitrous oxide injection systems in their engines. Today, some classes of car racing usually allow nitrous oxide applications.
Even so, before using nitrous oxide in these cars, automakers studied many factors and did precise calculations to ensure safety. These precautions are necessary because the injection system can cause destructive explosions under the hood.
The Chemistry behind Nitro Boost
In nitrous oxide engines, the decomposition of nitrous oxide produces the oxygen used in the combustion process. Since combustion occurs at a rate which is higher than average, the power output increases.
One mole of nitrous oxide produces half a mole of oxygen molecules (O2) and a mole of nitrogen molecules (N2) after decomposition. This decomposition process produces an oxygen concentration of 36.36%.
Air allows a 12% lower peak oxygen-level relative to that of nitrous oxide. The oxygen is mixed with fuel and produces carbon dioxide, water vapour and heat. This heat makes the other products to expand. The expanded components exert pressure on the pistons, which then drives the engine.
Tanks store nitrous oxide in its liquid state. In normal atmospheric conditions, it turns to gas. Cars fitted with nitrous engines are identifiable by the ‘purge’ of the delivery system. It is normal with drivers before getting to the starting line. The purge system, once activated, make plumes of nitrous oxide visible for a short while as the liquid changes to a gas.
The nitrous purge ensures that the right levels of nitrous oxide are injected. Injecting nitrous oxide adds more fuel to the engine and is a simple way to boost your car's engine power output without having to tweak it. That, however, doesn’t mean that you should hook up nitrous oxide tanks under the hood of your car to ease your commute.
Types of Nitrous Systems
The two types of nitrous systems are dry and wet, depending on the method used in delivering nitrous oxide into the intake manifold.
There are four conventional delivery methods:
- Single nozzle
- Direct port
- Plate
- Bar
The majority of nitrous systems make use of particular orifice inserts (jets) and pressure calculations to deliver the desired amount of the gas and create an efficient air-fuel-ratio for the boost required.
Here are the two types of nitrous systems:
1. Dry Nitrous System
Only nitrous oxide is delivered by the nitrous delivery method, which injects fuel through a separate channel, the fuel injector. Two ways to increase the amount of fuel flow - by increasing the pressure and by increasing the time that the fuel injector is open.
Although this system uses a single nozzle delivery method, it is possible to use the other methods. Carburetors are not capable of producing a high amount of on-demand fuel, and for this reason, you cannot use a dry nitrous system in carburetted applications.
2. Wet Nitrous System
In wet nitrous systems, nitrous oxide is combined with fuel and then delivered using the nitrous delivery method to the intake manifold. A special nozzle is used to measure the fuel and nitrous required. This system has an edge over the dry system because of its efficiency.
This system supports all the methods of delivery. One should be careful to ensure there are no backfires as a result of fuel pooling in the manifold or uneven distribution of the mixture.
This system can be redesigned to distribute the mixture to the combustion chambers evenly, making it viable for carburetted and throttle body injected systems.
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