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e30 mix with 93oct

Understanding AFR

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i watch some videos in the ethanol module but i still don't understand how to tune blends, for example i been tuning mazdaspeeds with cobb, now customers want to do ethanol blends but there is no ethanol kits for mazdaspeed so usually people just go by the tank is 16 gallons and they wanna run e30 of e85 the fill tank with 11.8 93 oct and 4.2 of e85. cobb in mazda only have a injector phasing multiplier, injector scalar and specific fuel gravity. if i change those numbers for the percentage of e85 the afr will be the same ? stoich 14.8 and at wot 11.7 for example or it will be different, also i would love to tune with lambda but in cobb you cannot just change the fueling in lambda it changes temperatures, grams per seconds, etc. into another units that I'm not familiar with. the maf is already calibrated for 93 oct. i will need to calibrated again ? and if i do i can use the same maf error trick ? sorry if i misspell something my 1st language is not English thank you in advance and i hope you could help me out

You appear to have made a math' error with the fuel percentages, using nominal values...

4.2 gallons of E85 has

3.57 g of ethanol and

0.63 g of gasoline

If you add 11.8 g of gasoline you get a total of 12.43 g,

add the ethanol and you have a total volume of 16 g of which 3.57 g is ethanol, this is a percentage of 3.57/16 * 100 or 22.31% which is E22.31

It looks like you've figured it out as a ratio which would be 12.43:3.37 or 3.48:1, which may be interpreted as 1:0.287 and somehow mistaken as 28.7 being a percentage, which is certainly isn't?

The ratio of fuels for E85 to make E30 is as follows - note, I'm using a 10 gallon base of E85 as it's simpler, and you can multiply/divide the numbers easily from it.

10 gallons of E85 has

8.5 g of ethanol and

1.5 g of gasoline.

For E30 we have to add enough gasoline to make the percentage of ethanol 30%, which is so for the 8.5 gallons of ethanol we have a total of

8.5 * (0.7/0.3) = 19.83 g of gasoline, so take away the 1.5 g we already have, we need to add 18.33 g of gasoline for every 10 g of E85, for E30.

That's a little impractical, but if we use slightly more gasoline, 1.9 gallons for every gallon of E85, we get E29.3.

Least ways, that's what my (literal) back of an envelope figuring gives me.

While lambda is usually the preferred method of measuring the fuelling, you may not be quite as badly off as you think. ALL AFR readings are calculated from the lambda values and if you have a gauge, scale, or whatever in AFR it will read the equivalent for gasoline/petrol - ie, stoich' is lambda 1.0 and the AFR will show the AFR as that, 14.7:1 IF it's calibrated for gasoline/petrol, regardless of what it actually is - might really be 12.5:1 if that's stoich' for that particular fuel blend.

Gord thank you for the response. i would love to tune in lambda but. in cobb if i change the values for lambda i have to click the box that says " show standard units" that will change not only afr to lambda, it will change all the values like psi to bar, gram/s to kg/hr, Fahrenheit to Celsius ect. it does not let me just chage the units for fuel tables only so im trying to fing a way that i can get to tune that blend with afr values

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Sorry, thought I'd added this comment.

While it's not technically correct, you could treat the "AFR" as a relative value. Use it as a variable for tuning by changing the number as required on the dyno', or use the value that would work if it was still running petrol/gasoline for "road tuning" - say 12.5-13:1 for power/torque, transitioning through 13.2:1 for moderate load, and maybe 15-16:1 for light load and cruising?

NOTE, don't get confused or, more to the point make sure anyone else who may be using the gauge AFR knows that's it's rtreepresentative, not actual values.

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