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Old 01-02-2007, 02:15 PM
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Charlie P.
 
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Default Just what is "Nitro"?

Nitromethane is used as a fuel in racing, particularly drag racing, to provide more power.[2] In this context, it is commonly referred to as "nitro" or just "fuel".

The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen in comparison to hydrocarbons such as gasoline:

4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2
14.6 kg of air are required to burn one kg of gasoline, but only 1.7 kg of air for one kg of nitromethane. Since an engine’s cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke. However, nitromethane has a lower energy density. Gasoline provides about 42-44 MJ/kg, nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen.

Nitromethane can also be used as a monopropellant. Without additional oxygen nitromethane will combust according to:

4CH3NO2 → 4CO + 4H2O + 2H2 + 2N2
Nitromethane has a laminar combustion velocity of approx. 0.5 m/s, somewhat higher than gasoline, thus making nitromethane suitable for high speed engines. It also has a somewhat higher flame temperature of about 2400 °C. The high heat of vaporisation of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge (about twice that of methanol), resulting in reasonably low temperatures. In a Top Fuel dragracing engine this alone will provide the cooling of the engine.

Nitromethane is usually used with rich air/fuel mixtures. This is partly because nitromethane can provide power even in the absence of atmospheric oxygen, and also because nitromethane tends to produce severe knock and pre-ignition. Rich mixtures cause ignition problems and a lower combustion speed.

When rich air/fuel mixtures are used, hydrogen and carbon monoxide will be two of the combustion products, when these and any unburned fuel comes into contact with the oxygen in the atmosphere at the end of the exhaust pipes they often ignite. The result is spectacular flames from the exhaust system.

A small amount of hydrazine blended in nitromethane can increase the power output even further. With nitromethane, hydrazine forms an explosive salt that can combust by using only the oxygen in the nitromethane. This mixture is unstable and it poses a severe safety hazard.

In model aircraft and car glow fuel, the primary ingredient is generally methanol with some nitromethane (0% to 65%, but rarely over 30% since nitromethane is expensive compared to methanol) and 10-20% lubricants (usually castor oil or a synthetic oil.) Even moderate amounts of nitromethane tends to increase the power created by the engine (as the limiting factor is often the air intake) and make the engine easier to tune (adjust for the proper air/fuel ratio) properly. During combustion, this fuel produces a characteristic blue smoke.

Nitromethane has also been used as a rocket fuel.
K. Owen and T. Coley, "Automotive Fuels Reference Book - 2nd edition", Chapter 13 "Racing Fuels", ISBN 1-56091-589-7 (1995)


CH3NO2; the simplest organic nitrogen molecule.

I see the word "Nitro" used around here frequently but sometimes with little apparent understanding of what it is and why it is added to glow fuel. Here is an authorative explanation. It adds a bit of power, burns a little cooler, allows leaner/higher RPM runs. It does not cure cancer or the common cold, perform miracles or allow automatic entry into Valhalla for it's users.