Methanol Injection AFR

[spyderturbo007]

Well, I posted this over on tuners and wanted to post it here for some additional comments.

Anyway, I'm trying to nail down the problems with using a WBO2 that's correlating it's Lambda value to a gasoline stoichiometric value of 14.7:1.

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) using a mass of 6.6lbs/gal.

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

From what I've read, the stoichometric 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?

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.

[scottsee]

I remember when I was trying to wrap my brain around that last year.. no fun.. This is what I use..

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:
(Mixture Stoich Value/WBO2 reading) x 14.7 = 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: (11.2/14.36) x 14.7 = 11.47 REAL AFR

[scottsee]

you can lean out pretty far on meth.. I go for 11.5 on pump gas 50/50 mix

[spyderturbo007]

I went through your formula, but mine was coming up opposite of yours. With your calculation, it looks like the WB is going to give you an observed value richer than the actuall AFR. When I ran the numbers with a 50/50 mix as opposed to your 75/25, mine came up with the WB showing an AFR leaner than the actual.

[kjewer1]

If your WBO2 is calibrated to display gasoline AFRs, I don't think it matters what fuel you use. Go by gasoline AFRs. And stoich should be irrelevant since you're injecting at WOT. Unless you're going to display in Lambda, I don't think you need to be cocnered about all this. I reserve the right to be wrng however, on the grounds of complete and utter intoxication.

[BeteNoir]

An oxygen sensor does not read out in A/F ratios, either for methanol, gasoline, ethanol or diesel. What a lambda sensor reads is the ratio of the partial pressure of oxygen in the exhaust pipe compared to outside the exhaust pipe. It reads out in millvolts and only in millvolts.

If combustion misfires exist, or if unburned air and fuel pass into the exhaust pipe, the sensor will read this condition as lean. It does not know what happened in the combustion chamber.

If we know the exact type of fuel being used and the exact compositionof the exhaust stream, it is possible to calibrate the milivolt readout to correlate to an air/fuel mixture. But if misfires exist, the engine is changed or the fuel is changed, it must be recalibrated.

Gasoline does not produce a stoic value of 14.7:1. That is merely a nominal value used for estimation. Each type and batch of gasoline has it own stoic value which can range from 14.1:1 to 15.3:1.

Since methanol is 50% oxygen and oxygen is not a fuel, it contains much less heat value. Water is also not a fuel. A 50/50 mixture of methanol and water would contain only 25% actual fuel. Consequently, a considerably larger amount of this mixture must be used to provide enough combustion energy.

But the lambda sensor would still only read the oxygen present in the exhaust stream.

[Thor06]

All this went WAY the fuck over my head, but I do have some advice... I would find a way to read knock before getting too deep in tuning.

[spyderturbo007]

Alright, it's be awhile and I wanted to update this thread and see if I can get some opinions. I finished installing the WBO2 today and went out to make sure everything was working properly. Made a 2nd gear pull and found that my AFR looked to be about 11:1 or there abouts. It was hard to look at the road and the AFR gauge.

Drove around a little bit and decided to make another pull in 3rd gear and now the WBO2 is showing me an AFR around 12.5:1. I did hook up the analog output to the ECU's rear O2 sensor input, but my freakin' logger batteries whet dead before I was even able to get a log.

The thing that is getting me, is my SAFC correction factors are all indicating that I'm running rich. They are about -30% which pretty much the correction for a 9.5:1 factory AFR. I'm not sure what's going on here because if I had a boost leak, I would see inflated rich AFR's as opposed to a lean AFR. The only thing I can think of would be an exhaust leak before the WBO2.

Why would there be such a difference between 2nd gear AFR's and 3rd gear AFR's? How in the hell do I check for leaks? We replaced all the exhaust gaskets when we pulled the DP to install the bung so I really don't see there being a leak.

Keep in mind, I'm running a 50/50 mix of MeOH and H2O through a 6 g/h nozzle. Also, I have read that people say their throttle body is normally cold after installing MeOH injection, but mine is not. I'm sure the MeOH is kicking on because the LED lights and I've had to fill the tank once already.

Any thoughts?