Not the same AFR question

[Blown&Injected]

Talking about the AFR's of different fuels, a friend with a supercharged Viper asked the following:

>>

OK, and this brings up the question....what A/F ratio is correct when running Meth the way we do. I posed this question on the Viper boards with no response.

Since we are all running different percentages of meth to fuel, and a meth/water mix for me, I guess the question is, what A/F ratio should we shoot for? One would think that if you were to go to say 12.5 to 1, that might indeed be way too lean with the meth in there?

<<

My thoughts:
Need to see if I can get a bite on this on the Buick board.

Running 100% meth, it would seem that the AFR should be shifted to the rich side since the ratio for meth is about 2x the mix for gasoline.

Then it seems that the systems for the Buick's replace about 25% of the fuel with meth if 3/4 gas should be about 11.5:1, and 25% of the mix is right at 6.5:1, so should 10.5:1 be about right?

Math says so, but all I have read says about mid 11's??? I have not noticed a different WOT AFR target for gasoline vs gasoline with meth.

 

[86gn]

I have seen in a few posts that 1 point richer should be a good starting point.

HTH

 

[Razor]

Depends how much fuel your replacing. The more fuel you replace with methanol, the lower the target. Typically its one point richer as a starting point. There was a video here of a 291 V6 that made over 1k HP.. on 91 octane. It was run at 10:1 AFR. The tuning guidelines need to be rewritten a little.

You use the hypothetical 25% replacement.. how do you know you need 25%? Why not 15%.. then if so, it impacts the target less.

You tune to make maximum power using the WB sensor you have as a reference. You lean it out as the power increases. One the power does not increase, you back it down. Easy. Not all WB sensor read the same AFR. Cant tell you how many Dyno's i've been to and seen the in car WB not read what the tailpipe WB sensor reads.

HTH

 

[Blown&Injected]

That makes sense.

Got my kit Monday - Razor, WOW, that pump is about the size of the starter motor on my Explorer!

 

[callmeebryan]

If you are reading off a WB.... then your AFR will read the same on regular gasoline as opposed to running methanol injection, if the same total amount of fuel is being injected. So if your total fuel usage at WOT is 300lbs/hr of gasoline... and your methanol pump is set to pump out say... 60lbs/hr of methanol, then you'll want to tune your total gasoline usage for around 240lbs/hr at WOT.... and so on.

Your WB is only reading the amount of oxygen that is coming through the exhaust. It doesnt care what kind of fuel you are running. In the end its just reading lambda, and AFR is a function of lambda.

 

[RmvBfrFlght]

If you are reading off a WB.... then your AFR will read the same on regular gasoline as opposed to running methanol injection, if the same total amount of fuel is being injected. So if your total fuel usage at WOT is 300lbs/hr of gasoline... and your methanol pump is set to pump out say... 60lbs/hr of methanol, then you'll want to tune your total gasoline usage for around 240lbs/hr at WOT.... and so on.

Your WB is only reading the amount of oxygen that is coming through the exhaust. It doesnt care what kind of fuel you are running. In the end its just reading lambda, and AFR is a function of lambda.

This isn't true. When rich of stoich there isn't any oxygen for the WB to read. And, a WB unit needs to be set up differently for different fuels. Has to do with the H & O to C concentration of the fuel. (looking for my notes on this. . .)

Here they are, can't find the ratios for methanol, however for gasoline they are:

H/C is 1.85
O/C is 0.00

For ethanol they are:

H/C is 3.00
O/C is 0.50

This has the affect of having a WB unit set up for gasoline (via O&H to C ratios) as reporting a richer then correct AFR for alcohols. The only WB units I've seen that has the ability to set these ratios, along with the % of O2 in the atmosphere was a lab grade NGK box (MO-1000) and the Horiba Mexa 110. I am sure that others will, but none of the hobby ones do.

RmvBfrFlght


{edit: found the ratios for methyl alcohol, (in the Horiba manual of course):

H/C is 4.00
O/C is 1.00

end edit}

 

[callmeebryan]

This isn't true. When rich of stoich there isn't any oxygen for the WB to read. And, a WB unit needs to be set up differently for different fuels. Has to do with the H & O to C concentration of the fuel. (looking for my notes on this. . .)

Here they are, can't find the ratios for methanol, however for gasoline they are:

H/C is 1.85
O/C is 0.00

For ethanol they are:

H/C is 3.00
O/C is 0.50

This has the affect of having a WB unit set up for gasoline (via O&H to C ratios) as reporting a richer then correct AFR for alcohols. The only WB units I've seen that has the ability to set these ratios, along with the % of O2 in the atmosphere was a lab grade NGK box (MO-1000) and the Horiba Mexa 110. I am sure that others will, but none of the hobby ones do.

RmvBfrFlght


{edit: found the ratios for methyl alcohol, (in the Horiba manual of course):

H/C is 4.00
O/C is 1.00

end edit}

Not when you read in lambda....

AFR changes.... lambda doesnt change... which is why its better to tune by lambda... but everyone isnt familiar with the lambda ratios and manufacturers have to appeal to the mass market .

BoostCreeps.com View topic - Methanol AFR Tuning

Your ratios are obvious.....

methanol = CH3-OH --> 4 hydrogens, 1 carbon, 1 oxygen
ethanol = CH3-CH2-OH --> 6 Hydrogens, 2 carbons, 1 oxygen

Some interesting stuff i want to add from my organic chem manual....

           Energy Content   Heat of Vaporisation   Oxygen Content    
              Nett MJ/kg          MJ/kg                   wt%
Methanol        19.95             1.154                  49.9
Ethanol         26.68             0.913                  34.7
Gasoline       42 - 44            0.297                   0.0

Gasoline is simply a bunch of alkanes mixed together... not bonded together, and has no oxygens bonded to it... or else it would be an ether, ester, or alcohol . A general rule of thumb for all alkanes is (C_n H_n+2).

 

[RmvBfrFlght]

Not when you read in lambda....

AFR changes.... lambda doesnt change... which is why its better to tune by lambda... but everyone isnt familiar with the lambda ratios and manufacturers have to appeal to the mass market .

BoostCreeps.com View topic - Methanol AFR Tuning

Your ratios are obvious.....

methanol = CH3-OH --> 4 hydrogens, 1 carbon, 1 oxygen
ethanol = CH3-CH2-OH --> 6 Hydrogens, 2 carbons, 1 oxygen

Some interesting stuff i want to add from my organic chem manual....

           Energy Content   Heat of Vaporisation   Oxygen Content    
              Nett MJ/kg          MJ/kg                   wt%
Methanol        19.95             1.154                  49.9
Ethanol         26.68             0.913                  34.7
Gasoline       42 - 44            0.297                   0.0

Gasoline is simply a bunch of alkanes mixed together... not bonded together, and has no oxygens bonded to it... or else it would be an ether, ester, or alcohol . A general rule of thumb for all alkanes is (C_n H_n+2).

You just changed from everything you said in your original post.

The fact remains that when rich of stoich there is no free O2 in the exhaust. The WB sensor reacts to the H & C content of the exhaust. Because of this a WB unit setup for gasoline will not report the correct AFR, Lambda or FAR for a fuel with alcohol in it.

To word it another way, a WB O2 sensor has a different calibration curve dependent upon the H/C and O/C ratios of the fuel being used. It does not matter if the AFR is reported in lambda or not. It is the calibration of the sensor that is different.

This is why folks are finding that as they add more and more methanol they need a richer then expected AFR. By expected it is for the ratio of meth to gas, a simple calculation. A WB unit which has a calibration curve for gasoline will show a richer then true AFR or lambda . The reporting unit doesn't matter. What matters is the calibration curve of the sensor which is either built into the controller, or is user set up in the controller.

RmvBfrFlght