Nitromethane (10-20%) in methanol

[obanion]

I was wondering if anyone here could comment (if familar) with the effective octane, detonation, and pre-ignition changes of adding 10-20% concentration (by weight) of nitromethane to methanol? Say compared to using nitrous oxide to achieve the same level of power enrichment?

I ask because after crunching some numbers, nitromethane seems to be a better choice, in my case.

The vehicle will have a dual fuel system. Gaseous propane for most conditions, and a second set of injectors injecting methanol (with possible nitro blend). The liquid fuel will not be used until full power is desired, basically WOT and above 15psi boost. So there won't be any of the usual concerns with the high expense of burning nitro when you don't want to.

Compared to nitrous oxide, it seems about 3x cheaper per HP/per minute to use nitro. Here's how I came to that...

Let's say I can make 500HP with methanol on turbo, no NO2 or nitro. I want 100HP of further power enrichment. This can be achieved with NO2 at about 10LBM flow. At $4/lb locally, that's $40/min burn rate with a 100shot.

To get the same 100HP with nitro, I would need 20% nitro, 80% methanol by volume.

500HP, 20% nitro, 20% more power, 500*1.2=600HP, 100HP difference.

80/20 by volume is 74/26 by weight, 6.63lb/gal methanol, 9.37lb/gal nitro, (9.37*.2)/((6.63*.8)+(9.37*.2))=.26109

Using a 1.7:1 stoich AFR for nitro, and 6.45:1 for methanol, that calculates the mix to be a stoich AFR of (6.45*.74)+(1.7*.26)=5.215 AFR.

6.45/5.215=1.2368, I'll need about 24% more MASS fuel to air.

The mix weighs (6.63*.8)+(9.37*.2)=7.178 lb/gal

7.178/6.63=1.083, or 8.3% denser than 100% methanol.

So I'll need 1.2368/1.083=1.142 or 14.2% more VOLUME flow with 80/20 than 100/0.

Now to finalize it, I assumed a BSFC of 1 for 100% methanol, which gives 8.33LBM, or 1.2569GPM, of 100% methanol for 500HP. Substituting the 80/20, that would be 1.2569*1.142=1.435 GPM of 80/20, which is 20% nitro, so 1.435*.2=.287 GPM of nitro. At $45/gal for nitro in most places, that's .287*45=$12.91/min of nitro for the same 100HP, that cost $40/min for NO2. I also saved a few cents by burning a touch less methanol.

So if there isn't a chemical reason to go with NO2 over nitro, then the cost savings will dictate my choice.

 

[patprimmer]

obanion

I also participate in another forum, HRE.com

It specialises in Fuel injection, exotic fuels and supercharging, mainly for drag racing, and mainly mechanical injection, and methanol and methanol/nitro methane blends.

We get a few older guys who have been involved with Sprint Cars, land speed record attempts, a few with EFI, or EFI mechanical composites, some NA, some Roots blowers, some Turbo.

Some guys have tractor pullers or mud thingos.

It is not a professional engineering site like this, but a real racers site. The administrator of the site is an old racer and as it is smaller, it is more personal and more liberal.

It is certainly not a replacement for this site, but might give a different perspective, and will not put you in danger of red flags for hobby type questions.

The administrator also publishes a manual with a LOT OF INFO re fuel, mixing, specific gravities of blends, at various temperatures, nozzle size charts, formulae for calculations of pump size and fuel delivery etc etc etc.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[obanion]

Thanks, I'll take the question there. You may delete this thread if you like.

 

[patprimmer]

I think the thread can stand here, and might get some different perspectives.

Some absolute back yard hobby threads survive even when the question shows no engineering knowledge, but not often.

Some professional racers get red flagged, but not often when the questions does show some in depth knowledge as yours do.

As I understand the site rules, home repair men and armature hot rodders don't belong here, professional repairers and armature racers are borderline, professional race car developers do belong. Your work sounds like professional level race car development to me, even if it is your own car.

Professional and work related seems to be the main criteria. Professional is NOT necessarily certified, as it is recognised that many all time great engineers were self taught, or trades background, like the Wright Bros and Henry Ford for instance.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dynoguy]

This is quite the setup you describe: three fuels of propane, methanol and nitro- AND a 15 psi turbo? There has to be an easier way to make 600 HP! Is this one of those bait questions to see who falls for it? (if so, you got me!)

How about a 501 chevy crate motor with a WOT nitrous system?

Since I've heard the octane of Nitro is -1000, and since turbo motors like to devour themselves when they pre-ignite, I'd think simpler is better. Let us know what you settle on.