Methanol and stoich mixture?

[gibby]

Stoich for methanol is 6.4:1, for gas it is 14.7:1. So if you are fueling with 30% methanol 70% gasoline, stoich is 12.2:1?

Soooo if your wideband shows 12.5:1, without much thought you would say you are rich relative to stoich (for gasoline of course), but in fact you are lean for the new theoretical stoich fuel mixture?

What kind of A/F's do you guys shoot for? I just got my hands on some methanol, so I am ditching the -20 washer fluid to play around starting with a 50/50 mix, what basic* tuning changes should I be looking to make? I won't be using anywhere near 30% methanol for my fueling, just doing some simple math to make this point. Hopefully you guys have some input?


*not asking for specifics, I am SC not turbo, different PCM, etc, just looking for pointers in the right direction, mostly talking theory here.

 

[Razor]

Well.. non of us run WOT at Stoich. And the 30% number.. maybe all you need is 10%. Plus what does the water do to your AF?

The typical way these systems are tuned is make a richer target, like 11.5:1. Now observe performance at this number.. vs 11.7 or 12.0.. the more water you mix in, the higher the target.

If you pickup knock.. add volume of methanol.. and then pull out fueling to get back to your AF target.

Lets start here

 

[gibby]

Yeah, 30% was easy math, I doubt I am even using 10%. I know we run richer then stoich at WOT, which is exactly my point: what if you add enough methanol to be too close to the stoich a/f for both fuels combined? Just to illustrate, say you run 50% methanol 50% gas, your stoich is around 11.8:1, you start out tuning by shooting for 12:1, and you are in fact lean.

Is that even a concern? Probably not, you would pick up knock before you got too close. What I am saying is, 11.5:1 is X percent richer then 14.7:1 on a gas only engine, but it is X-Y percent richer (relatively leaner) when using methanol as a fuel, in other words leaner compared to stoich......

Water should do nothing to the A/F, theoretically it does nothing but displace cylinder volume, having the effect of richening up the mixture ever so slightly due to the unmetered volume of water that is taking the place of some air, just a knock suppresant and safety factor. Gotta get those M90 outlet temps down somehow.

I was just thinking theory here, I got the basics down by starting on the wet side of mixtures (0 degree washer fluid ) and figuring out how to tune for it, now I think I'm ready to get a little more serious. Mostly looking for opinions on this stoich for combined fuel, I figured you guys would have them, and I'm all ears :biggrin:

 

[Razor]

Water displaces fuel and creates a leaner condition.

Splitting atoms wont tell how us how to make more HP on your particular motor. Start rich, work lean observing performance. If you lean it out and it doesnt pickup.. leave it at the richer setting.

Trying to come up with a specific AF it should be at becuase of the methanol thats being introduced..has never worked. As there are too many other variables in play.

Stop using WW fluid. If your going to run mix.. mix it yourself. Else your tuneup is in the hands of whoever mixed the WW fluid.. and any additives not listed in the label.. like ammonia.

 

[gibby]

Gotcha. I can get methanol for cheeeeeap in Tulsa, $2.10 a gallon, but I know WW fluid is far from ideal.

I figured there were too many variables to be sure about an exact ratio, never hurts to ask though. Thanks

 

[Alky V6]

If your wondering what stoich is when mixing fuels, it will depend on how your O2 sensor is setup. If your sensor is setup to read out stoich as 14.7, then stoich will always be 14.7 no matter what fuels you are burning. I run 100% methanol and my sensor read out has always been setup for gasoline A/F reference numbers. I just read it as if I'm burning gasoline. Idle A/F is 13.4 to one, WOT lean best torque is 13.3 (very dangerous for blown alcohol), WOT rich best torque seems to be around 12.4 to one, although I run mid to high 11s to one at WOT to be safe. You must remember that the O2 sensor is reading left over oxygen after combustion. That is all. It doesn't care what the fuel is, it is only reading oxygen. When the least amount of oxygen is present, the more complete the combustion process. I believe that is stoich.

 

[gibby]

Thanks, thats exactly the type of info I was looking for

Just started using a 50/50 mix, and I am riiiiiiiiiiich. Time to pull some fuel, I really need to hook up my wideband :redface:

 

[Pablo]

What don said

wide bands dont measure air fuel ratio, they measure what I believe they call lambda which is just the representation of how much fuel vs air is left in the exhaust, the fuel and the air are equally exhausted in the burning of the fuel.. that would be stoichiometric.

the wideband just says 14.7 for stoich because it assumes you are using gasoline, it would also say 14.7 if you were running pure methanol even though the actual air fuel ratio would be 6.4:1

obviously, tune for best performance, but that should look just like you are tuning pure gasoline on your wideband which is gonna be mid 11s af ratio wise most likely... its just measuring a percent of how much past stoich you are going. The number it gives you is extrapolated from just an assumption on what fuel you are running.

Hope that makes sense, I'm no expert on it, I just know thats what you end up with.