Nitromethane

[Robert Harris]

Reference: High Performance Automotive Fuels and Fluids
Author: Jeff Hartman   Publisher: Motorbooks International.

The first thing to remember about nitromethane is that is a rocket 
monopropellant.  Quite simply, if you can cause ignition, nitro needs no 
additional source of oxygen or anything to continue to burn.  Thus, if 
you could ignite it, you could fill the chamber to hydrolock with nitro 
and generate massive power. (Hint - it's 56% by weight oxygen).  

Next, stoichiometric combustion of nitromethane yields 5.82 moles of 
product for 4.87 moles of intake charge reactants.  This is about 127%, 
whereby gasoline or alcohol yeild 106%. At very rich mixtures this goes 
up to 160%.  Since stoic ~ 1.7 to one, and 1 to 1 is where most seem to 
go with it - you get the picture - you typically burn 12 to 15 times as 
much nitro with the same amount of air as gasoline and you get twice the 
bang for each kilogram.  Double A fuelers are getting an estimated Six 
Thousand plus HP out of  500 cubic inchs

Since it burns once ignited without regard to external oxygen, most of 
the chemical anti-detontants work poorly or not at all. It has a low 
heating value, but since its specific energy is over twice that of 
gasoline, and with the same amount of air you can burn over 12 times the 
ammount as with gasoline, you can generate enormous amounts of power, 
product and temperature. Its latent heat of vaporization is about .5x vs 
gasoline at ~.2x so its does cool the intake charge somewhat.  

Excerted SAE tables in the above reference show that nitro lowers the 
octane of a toulene/acetone/alkylate base fuel significantly, a 10% 
nitro mix results in 99 RON and **** 75.4 **** MOTOR octane (about  7 
numbers lower than the cheapest unleaded crap at the stop and rob) and 
thats with 25% straight Toulene ( higher octane than methonal - 
depending of course on who's research you reference ) in the mix. Might 
give you a clue of the octane of neat nitro.

Most references, including personal conversations with fuel dragster 
racers, consider nitromethane in any significant quantity to be 
extremely detonation prone and that the only reason the alcohol is in 
the mix is to cool the combustion below the point where the metals 
themselves contribute to the combustion product.

Because of the extreme molar product, heat of combustion, low motor 
octane, propensity to wildly pre-ignite and detonate and because every 
reference says so, I would hazard to guess that lower Compression ratios 
are normally used with nitro/alcohol blend than with a straight alcohol 
or racing gasoline fuel.  Of course since I'm an Expert - NOT, me and 
the references could be wrong for which we will gracefully accept a CSH 
and return to the corner.


>Frederic Breitwieser wrote:
>> 
>> >Are you sure that nitro requires a higher CR? I've heard the exact 
opposite.
>> 
><SNIP>
>
>Gotta remember,,, Nitro and alcohol allows a cooler burn,,, which, in
>turn, allows for some 'benefits' else-where.
>


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