USED AS AN ENGINE FUEL:
In a minor application, nitromethane is used as a fuel in racing, particularly
drag racing, as well as for rockets and RC Models. In car racing, nitromethane
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 is 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.
Nitromethane, however, has a lower energy density: Gasoline provides about
42–44 MJ/kg whereas nitromethane provides only 11.3 MJ/kg.
Nitromethane can also be used as a monopropellant, i.e., a fuel that burns without added oxygen.
The following equation describes this process: 4 CH3NO2 → 4 CO + 4 H2O + 2 H2 + 2 N2
Nitromethane has a laminar combustion velocity of approx. 0.5 m/s, somewhat higher
than gasoline, thus making it suitable for high speed engines. It also has a somewhat higher
flame temperature of about 2400 °C. The high heat of vaporization 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.
Nitromethane is usually used with rich air/fuel mixtures because it provides power
even in the absence of atmospheric oxygen. When rich air/fuel mixtures are used,
hydrogen and carbon monoxide are two of the combustion products. These gases
often ignite, sometimes spectacularly, as the normally very rich mixtures* of the still
burning fuel exits the exhaust ports and out through the exhaust pipes. [* the very rich
mixtures are necessary to reduce the temperature of combustion chamber hot parts so
to control Pre-ignition and subsequent Detonation]
Note: The preceding Paragraphs refer to conditions where the volume of
Nitromethane blended with Methanol => 80%.And with a typical 500 cu. in.
Drag Racing Engine producing now* in excess of 8000 HP. *Aug. 2007.
A small amount of hydrazine blended in nitromethane can increase the power output
even further. With nitromethane, hydrazine forms an explosive salt that is again a
monopropellant. This unstable mixture 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 and/or synthetic oil).
Even moderate amounts of nitromethane tend to increase the power created by the engine
(as the limiting factor is often the air intake), making the engine easier to tune (adjust for the
proper air/fuel ratio).