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     Dr.(Phys.)Dipl.-Ing.Ralf-Udo Hartmann

Nitromethane

I try to explore some of the other alternative fuels, alcohol, and nitromethane.

Gasoline - Gasoline is what most of our cars came setup so it's usually what we stick with. Gasoline is a mixture of hydrocarbons. The petroleum distillate fraction termed "gasoline" contains mostly saturated hydrocarbons usually with a chemical formula of C8H18. The air fuel ratio, A/F Ratio, for complete combustion is 14.7:1, stoichiometric. The A/F ratio for maximum power is approximately 12.5:1 - 12.8:1. This means that our engine at max power, 12.8:1, consumes 12.8 pounds of air for 1 pound of fuel. Gasoline has approximately 18,400 BTU/lb . Using the air flow calculator with the default inputs we get our 355 SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and consumes 2.89 pounds of fuel. Therefore if we are using gasoline our engine is producing 53,176 BTU's of energy at 6500 rpm.

Alcohol (Methanol) - Alcohol is usually used in the form of Methyl alcohol or methanol. CH3OH is the chemical formula. Methanol burns at a much richer mixture than gasoline does, between 5.0:1 - 6.0:1. That's 5 lbs of air to one pound of fuel. Methanol has approximately 9,500 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 6.0:1 ratio for Methanol is 7.11 pounds of fuel. Therefore if we are using Methanol fuel our engine is producing 67,545 BTU's of energy at 6500 rpm.
 
 

Nitromethane - is a fuel that is used mostly in specialized drag racing classes, "nitro funny cars" and "top fuel". Nitromethane's chemical formula is CH3NO2. The oxygen in nitromethane's molecular structure means that nitromethane does not need as much atmospheric oxygen to burn, part of the oxygen needed to burn nitromethane is carried in the fuel itself. Typical A/F ratio for nitromethane is 1.7:1 and nitromethane has an energy content of 5,000 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 1.7:1 ratio for nitromethane is 25.08 pounds of fuel. Therefore if we are using Nitromethane fuel our engine is producing 125,412 BTU's of energy at 6500 rpm.


Summary - As you can the clear winner is nitromethane. But that doesn't mean to go out and pour nitromethane in your car and see how it runs, if you do your engine will surely blow up. Nitromethane is very expensive and dangerous to handle. The interesting alternative to gasoline is Methanol. Methanol will make more power, typically around 20% more power than a similar engine running gasoline. Some things to consider in running methanol is your fuel system will have to be completely changed / upgraded. Based on the table above the fuel system will have to flow approximately 2.5 times as much as the gasoline engine.

I guess the old saying is true.
 
"Gasoline is for washing parts, alcohol is for drinking and nitro is for racing."

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.
 
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