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Nitromethane is used as a fuel in drag racing to provide more power than would be available with gasoline or with alcohol. When you hear the term "nitro funny car" or "top fuel dragster", that means that the engine burns nitromethane. The chemical formula for nitromethane is CH₃NO₂. For comparison, a typical gasoline molecule is C₈H₁₈. Nitro thus can be seen to have oxygen as part of its' chemical composition while gasoline does not. The oxygen content of nitromethane means that not as much atmospheric oxygen is needed for combustion, part of the oxygen needed to burn nitromethane is carried in the fuel itself.

Due to the high oxygen content, while 14.6 pounds of air are needed to burn a pound of gasoline,  only 1.7 pounds of air are needed per pound of nitromethane. A motor can only take in so much air on each stoke, and with that amount of air you can burn 8.7 times more nitromethane than gasoline. The energy content of gasoline is ~18,000 BTU/pound while nitro has ~5,000 BTU/pound. By pumping in 8.7 times as much nitromethane per stroke, you get about 2.5 times more power per stroke. 

The speed of combustion for nitromethane is much less than for gasoline, meaning that there is not enough time to burn all the nitromethane in the cylinder when the engine is running at high RPM. When the exhaust valve opens, nitromethane that is still burning flows out through the exhaust pipe. That is why funny cars and dragsters have visible yellow flames from their exhaust pipes.

Nitromethane as a fuel additive.

We are sometimes asked about adding nitro to gasoline or methanol. This is possible and it has been done successfully. However, there are a number of problems that make this impractical. These include the corrosive nature of the combustion gasses after nitromethane is burned. This process produces large amounts of nitric acid, which is not only corrosive but toxic. To prevent serious corrosion, a thorough flushing of the fuel system and motor is necessary after use. While it burns slowly, there is also the danger of explosion when nitro is used. Another issue is solubility. If you are running methanol, there is no problem as nitromethane and methanol mix freely. But nitro does not mix easily with gasoline. So, if a nitro/gas mixture is desired additional chemicals must be added to prevent separation.

Nitropropane - an alternative to nitromethane.

Both nitromethane and nitropropane are oxygen-bearing fuels. This means that nitro fuels carry two oxygen atoms as part of their chemical makeup. While nitromethane (CH₃NO₂) does not mix with gasoline, nitropropane (C₃H₇NO₂) does. This makes it much more practical as an additive. A commercial mixture of nitropropane and antidetonation agents is available under the "Klotz" brand. Mixtures of ~10% nitropropane and gasoline have been tested and shown to provide small but significant power increases. A good writeup on this was published in "Hotrod" and is available online at http://www.hotrod.com/techarticles/42018/ If you decide to try this, you must richen the fuel mixture and even then you can destroy your motor, so try this at your own risk!

Nitropropane