We have a car at the shop that runs at the bonneville salt flats. It is setup for a displacement limited/ naturally asspirated class. It is a highly tuned setup/ matched combination (I would rather not say what engine it is) and we are at the limit of the horsepower we can make it produce.

The engine runs on methanol but the class rules allow any fuel (including nitromethane, CH3NO2). A few weeks ago we did some preliminary dyno tests on the engine using nitromethane. We started with low percentage mixtures ( 3%, 5%, 10%, ...). We worked our way up to a 30% mixture. Each step of the way we checked for detonation and watched egts (our lambda meters are not usefull with nitromethane). The egts stayed constant as long as when we used a higher % nitro we also bumped the fuel trim up.

We had to cut the test short to get the car ready to run but we ended up making an additional 50-55 horsepower (~7% gain) but I think we can make more. It occured to me that methanol and nitromethane are each going to have an exact (different) stoichiometric mixture to combust with air. The amount of air coming in is fixed, but we can change the amount of fuel and the % mix. Does this mean that there is only one % mixture of methanol to nitromethane that will result in a good air fuel ratio for both the nitro and the methanol? How can I figure it out (I need to brush up on my chemistry)?

Also, we were mixing the 2 parts based on mass. Is this the normal way to do it? Our thinking was that if you mix based on volume, temperature will affect density and you don't really know what mix you are getting.

Does anyone have any input that might help us out?

Thanks
Dustin

 

You might start with these links:

http://www.turbofast.com.au/racefuel8.html

http://www.turbofast.com.au/racefuel6.html

http://www.turbofast.com.au/racefuel7.html

Good luck, and be very careful!

 

Thanks for the links, they help quite a bit. We are doing our best to keep everything safe. We have been taking it slow and monitoring each step. We have not seen any elevated egts or any signs of detonation.
However, I think we might have reached the limit of the injectors. Every time we run a higher percent nitro, the engine responds well to trimming the fuel higher (this observation was backed up by the links you gave). After multiplying the VE tables by 1.25 then trimming 125% from there, we are getting a pretty high duty cycle.

Does anyone know about the "perfect" ratio of Nitro to methanol? It still seems to me that there is only one possible mixture that will give you a proper stoichiometric combustion of both the Nitromethane and the methanol.

Thanks
Dustin

 

I don't think there is a "perfect" ratio. Top Fuel/Funny Car is now mandated by NHRA at 85% max nitro. It was previously 90%. Years ago guys were near 100%. NHRA tries to keep speeds and costs down by gear rules, nitro % rules, etc, but it doesn't help much. When the went to 85% recently speeds dropped off until they started pumping more total fuel into the engines, and power and speed went back up.

Your engine is a far different case from 6000-8000? hp Top Fuel engines.

Stroker McGurk said something that applies to nitro:

"If some is good, and more is better, too much is just enough!"