Thread: Nitromethane and alcohol ?'s

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Tech1, Thanks for the kind words. There are easy answers and complicated answers. First the easy answers at

http://www.nitromethane.com/

There we see the "autoignition temperature" of 315 degrees C similar to the 320 value you mentioned. Of more interest is the autoignition pressure of 62.3 atm. That high pressure seems out of reach but simple Diesel engine considerations show that compression ratios as low as 12:1 can approach such pressures and also easily exceed the autoignition temperature so it would be disastrous to use nitromethane in a diesel engine with a typical compression ratio of 22:1, that would give new meaning to the term "engine knock"! That explains why comments above refer to high concentrations of nitromethane used in low compression engines. A little surprise to me is the fact that the boiling point of nitromethane is about 103 degrees C and higher than I recalled, but there are numerous warnings to DO NOT DISTILL NITROMETHANE! Another site gives the Racer's viewpoint at

http://ch3no2.com/

Now for some complicated answers I note that a certain Prof. Smook at Cornell University has made extensive studies of just burning methane with oxygen and found it takes over 100 individual processes to describe all the reactions in such a "simple" flame. Other research by the Air Force (AFOSR) is well established in using models of many hundreds of reactions going on in a jet engine to explain such "combustion". The point is that in a "flame" there are many transient chemical species that don't last very long but are still there in the overall reaction so it looks like methane would burn simply as

CH4 + 2O2 -> CO2 + 2H2O + heat

but actually there is a whole lot of hot stuff going on! One further point is that research on energetic materials is where calculations can be very useful to investigate the energy of reactions using computer calculations without doing dangerous laboratory tests. Overall the key idea is that almost all such materials involve unstable organic nitro compounds. In research there are lists of many nitro compounds of varying explosive violence but of course you have to stabilize them somehow for sensible use and that is where the money comes from for the Nobel Prizes, the invention of stabilized TNT by Alfred Nobel. I want to stick to just racing fuels here since the topic of explosives on an open Internet site is not a good idea these days. To cover my rear I warn that nitromethane can be ignited by shock or heat over 315 degrees C but if a racer is careful and the driveline is prepped for the abuse, limited amounts of nitromethane "fuel" can give tremendous power boosts.

Don Shillady
Retired Scientist/teen rodder

How we limited the amount was the biggest pump we could get and a fuel tank that had some left at the end of the quarter

Maybe I glossed over a detail. While you can write a simple equation for a combustion reaction, in the actual event there is a lot of "hells-a-poppin" collisions between hot molecules that break bonds to give broken pieces with an odd number of electrons while nature prefers compounds with an even number of electrons. They break more until some even combination of electrons is reached in the final results at a lower energy. While an engine running at 5000 rpm only fires 2500 times per minute that is a relatively long time of about (2500/60) times per second or about 0.024 seconds per explosion. Compare this to molecular collisions of about 10**30 collisions per second in one cubic cm (about 0.061 cu in). That is about (1 million)x(1 million)x(1 million)x(1 million)x(1 million) collisions per second in one cubic cm. This means that to study combustion reactions the formation and destruction of many intermediate fragments of molecules have to be accounted for and so once nitromethane gets started fragmenting, that O2 part can come off and be available for reaction to form CO2. Even at high rpm the mechanical parts of an engine are moving much slower than the chemical reactions.

Don Shillady
Retired Scientist/teen rodder

Don,,, in order to keep all this 'fathomeable). Hot rodders past and present, for the most part, are able to grasp the anatomy of combustion on the molecular theory,,,, 1 atom fuel ($) 1 atom air (no typo) $ 1 match and we have ignition. Fortunately and unbeknownst,,, we have a cumbustion chamber floor (the piston) that readily heads south to escape the hostile environment and thusly converts our thermal energy into rotating energy. Feeding the monster huge amounts of volatile fuel, may sometimes not be digestable,,, In my blown pickle fork boat, I was always mindful of disaster and used aluminum bolts to secure my huffer,,,, better my Littlefield go on a leash, than my crank going out the bottom,,,, ps. I like your input