methanol a/f ratio's

[spyderturbo007]

Well, I'm bringing this back from the dead because I'm starting to deal with this problem. I have the MeOH injection installed and the AEM WBO2 is in the mail. I'm running a 6gph nozzle and a 50/50 MeOH to H2O mix. This is what I'm thinking.....

Max airflow I've seen for my setup is around 33.5lbs which gives me an "estimated" IDC of 73% on 650's and a total flow of about 1900cc /min of fuel.

I'm injecting 378cc/min of the MeOH mixture, of which only 166.96cc/min of that is MeOH (by mass).

That's a ratio of 8.8% MeOH and 91.2% fuel.

From what scottsee posted, the stoich point for MeOH is about 6.4:1 and we all know that fuel is 14.7:1. I'm attempting to shoot for a AFR of 11:1 for right now, since I can't log knock. I'm assuming that you can go leaner with the MeOH injection, but I have no idea how much leaner you can go.

Anyway, I'm trying to back calculate to the Lambda value, since the gauge will be calibrated for gasoline and assume a stoich point of 14.7:1. Assuming a linear relationship and the % fuel and MeOH give above, it looks like my mixture will have a stoich value of 13.77:1. Did everyone get the same answer I did? So, if I'm shooting for an AFR of 11:1, I should be looking for a Lambda value of 0.80.......correct? The thing that's confusing me here, is that scottsee's observed AFR is richer than the "real" AFR. According to my calculation, using his formula, my observed AFR would be leaner. Am I missing something?

Which, on the gauge, would be an AFR of 11.76. Does that sound right? By the way, does anyone know the sweet spot for a 50/50 mix? It's been proven that DSM's like to run an AFR of about 11:1 on pump, but I don't see anything concerning MeOH injection.

 

[T9S1i]

keep in mind your egt's. Methanol burns hotter than gas, so if you take it leaner than its supposed to burn its going to get things hot. Thats why i always shoot for an a/f ratio of somewhere in the 10's when i was using methanol. from what everyone was saying that was probably really somewhere in the mid/high 11's so thats about right.

My second week of tuning with my methanol i kept leaning it out and wasnt getting knock, but my egt's were really high and i even fried my alternator that night like i wasnt running a heat shield. My damn coil pack messed up a few days later and i had a misfire while doing a pull and baboom... rod through the block. CEL never came on for knock, i could hear the misfire and didnt get out of the pull, the a/f ratio was right about 11.1-11.2/1... my dumbass fault for boosting while spraying methanol and having a problem with my car. Learned that lesson...

But be careful about the heat. i know nobody has egt gauges anymore, but you dont want to be too hot by the top of 3rd/4th

 

[1SloColt]

Methanol burns hotter than gas

Methanol motors actually run quite a bit cooler than gasoline motors. EGTs will also fall about 400 degrees or so.

 

[T9S1i]

Really? I read somewhere that it burns hotter at its Stoich a/f ratio. I'll have to find out where i read that. Maybe it was what my friend told me...

If im wrong i stand corrected...

I was under the impression that it cooled the intake charge by evaporation, and added octane to the fuel, but burnt hotter than gas. One of the reasons i removed my methanol. i have to get basic tuning down before i add another variable to the equation. Its just something else to f me up at the moment, when i have a more comprehensive knowledge of tuning and more experience, i'll probably re-install my methanol so that i can get more power from my setup on pump, but until then its sitting in a box in my basement.

 

[SpeedAddict62]

I noticed some errors in these calculations.

Stoich Values:
Gasoline = 14.7
Methanol = 6.40

Weight:
Water = 8.33lbs/gal
Methanol = 6.59lbs/gal

Specific Gravity:
Gasoline = .737
Methanol = .791

Specific Gravity Differences:
Gasoline = 1.07 more dense than methanol
methanol = .93 less dense than gasoline

Equation to get Percent Methanol to Water Injection by Mass:
(Methanol Weight per Gallon)(Volume of Methanol in Mixture) = Methanol Total Mass
(Water Weight per Gallon)(Volume of Water in Mixture) = Water Total Mass

(Methanol Total Mass)(100)
(Meth Total Mass) + (Water Total Mass) = Methanol Percent by Mass

Equation to get Actual Percent of Methanol Injected:
(Methanol Percent by Mass)(Total Percent of Water Injection Mixture) = Methanol Percent Injected

Equation to get Mixture Stoich Value:
(Meth % by Mass)(Meth S.G. Difference)(Meth Stoich) + (gas %)(gas S.G. Difference)(gas Stoich) = Mixture Stoich Value

Equation to get REAL AFR:
(WB02 reading/14.7) x Actual stoich AFR = REAL AFR


Example:
75% meth injection to 25% water by volume at 20% of fuel delivery and a WBO2 reading of 11.2:1AFR.

Percent Methanol in Water Injection Mixture by Mass:
(6.59lbs/gal)(.75) = 4.9425

(4.9425)(100)
4.9425 + 2.0825 = 70% Methanol by Mass of 20% Water/Methanol Injected

Equation to get Actual Percent of Methanol Injected:
(70%)(20%) = 14% Methanol injected to Fuel

Mixture Stoich Value: (.14)(.93)(6.4) + (.86)(1.07)(14.7) = 14.36

Real AFR: (11.2/14.7) x 14.36 = 10.94 REAL AFR

So the wideband reading will be leaner than the actual AFR.

 

[spyderturbo007]

I pulled this quote from another thread, since I think this discussion should be moved over here. We were starting to jack turboglenn's thread.

Your actual AFR is leaner than that (by how much depends on the % meth injection compared to fuel). Read the thread below. There's a lot about this on the DSMlink forums and more on how to calculate your true AFR based on what the wideband tells you.

SpeedAddict62, this was your response to jlado's comment:

Wrong. It wouldn't be leaner, it would be richer.

But in this thread, post #30, you responded by saying:

So the wideband reading will be leaner than the actual AFR.

I'm trying to figure out what's going on here, since I tend to agree with Scottsee on this one, in that the WBO2 will show you richer when looking at AFR.

 

[SpeedAddict62]

Yes, I agree, it fits better here.

What I'm trying to say is that the wideband AFR will be leaner than your actual AFR, with a mix of gas and methanol. This makes sense to me, because for the meth/gas mix, in order to achieve the same lambda, it would require a richer actual AFR than for straight gas.

If you look at post #30 in this thread, I changed what I thought were mistakes in the calculations. If you redo the calculation, the actual AFR comes out to be 10.94:1 with a wideband displaying 11.2:1.

I simply used the fact that lambda = (actual AFR/stoich AFR)

In the above example, you could also do it this way. Set lambda of the two mixtures equal to each other. So:

(wideband AFR/stoich gas AFR) = (actual AFR/stoich gas/meth mix AFR)

Then we would have, from Scottsee's example,

(11.2/14.7) = (actual AFR/14.36)

Again, you get actual AFR to be 10.94:1 with the meth/gas mix.