[AltecBX]

These are technical facts of the fuel we use:
Fuel .......................... AFR
Gas stoich ................. 14.7
Gas max power rich .... 12.5
Gas max power lean .... 13.23
E85 stoich .................. 9.765
E85 max power rich ..... 6.975
E85 max power lean .... 8.4687
E100 stoich ................. 9.0078
E100 max power rich .... 6.429
E100 max power lean ... 7.8

Based on these numbers I came up with a simple calculation on the amount of E85 we should be blending to make full power. We run max power when running 14.7 on gasoline. On E85 the lamba is lowered to 9.765. This is the reason we can raise the boost since the vol of fuel needed is decreased.

Now what I did was take gas 14.7 & E85 9.675 and divide the two = 1.505376344
Then I divided E85 9.675 into the number above (1.505376344) & got = 6.48675
Now 6.48675 * 1.505376344 = E85 stoich (9.765)
Then I subtracted gas 14.7 - e85 9.765 = 4.935
I then divided that sum (4.935) into (1.505376344) & got = 3.27825
Now 9.765 + 4.935 = 14.7 (lamba 1) max power
These leads me to believe that we should be using 64.9% E85 with a mixtures of 32.8% of gas. We then can add the additional percentage of gas since there is 10% of ethanol in our gas.

65% of E85 / 35% of Gas for max power

Of course you need the proper hardware to achieve the flow of fuel (LPFP) & a tune to change ECU. And yes you can run higher percentage of e85 as it has a higher cooling effect on the intake charge

Open for discussion.

[VNeBLOB42]

Nice write up!

So based on 16 gallon tank, per your percentages that'll be 10 gallons of E85 pump and 6 gallons of premium? Which is a maximum of E57.

[AltecBX]

Originally Posted by VNeBLOB42

Nice write up!

So based on 16 gallon tank, per your percentages that'll be 10 gallons of E85 pump and 6 gallons of premium? Which is a maximum of E57.

Thanks.
Well we have a 16.6 gal tank on our 3 series (E9x) platform including the reserve. So the percentage will be 10.80 gal of E85 and 5.80 gal of gas.

[BMWM.D.]

I'm trying to follow your logic here.....

14.7:1 is stoich for pure gasoline, but it isn't where engines usually make max power. Stoich for E85 is much richer -- which means MORE fuel is needed to maintain a similar lambda reading. This is the reason I tune my C6 using lambda instead of AFR. Lambda=lambda=lambda, regardless of what fuel you are running. Forced induction engines usually make best power at ~.80 lambda or so.

With that aside, I'm not sure what the stoich AFR of ethanol or gasoline has to do with making max power. I'd say the more E85 you can support with a given fuel system, the more power potential you have. More octane + better cooling = the ability to run more timing/boost on a given combination.

[BEAR-AvHistory]

Does a base of 91 or 93 octane fuel for the gas side make a difference in the mix %?

[V8bait]

Originally Posted by BMWM.D.

I'm trying to follow your logic here.....

14.7:1 is stoich for pure gasoline, but it isn't where engines usually make max power. Stoich for E85 is much richer -- which means MORE fuel is needed to maintain a similar lambda reading. This is the reason I tune my C6 using lambda instead of AFR. Lambda=lambda=lambda, regardless of what fuel you are running. Forced induction engines usually make best power at ~.80 lambda or so.

With that aside, I'm not sure what the stoich AFR of ethanol or gasoline has to do with making max power. I'd say the more E85 you can support with a given fuel system, the more power potential you have. More octane + better cooling = the ability to run more timing/boost on a given combination.

+1

Whatever logic he used, was based on some underlying misconceptions.

[09BMW335i]

So, if i am follow this correctly my AFR should be around 6-7 with 10 gallons 93 and 6 gallons E85 i will be about 98 octane and that is the best place and most power? Or am i completely wrong?

[Mangler]

Guys the AFR readings with E85 are the same. Do you think we would have made it this far with people running 11's and 12s AFR? The wbo2 is scaling the reading with the additional fuel.

[V8bait]

AFR is a calculated value from lambda.

O2 sensor does not know how much gas has been injected into the engine. O2 sensor does not know how much air was drawn into the engine. It only knows if the small sample it tastes is rich or lean, as measured from a stoichiometric ideal ratio of oxygen to fuel (aka lambda of 1)

I'll give you a quick example. The car reads the O2 sensors in lambda. When you are idling, lambda is 1. The DME will report this as 14.7 since it thinks you have gasoline. If you are running 100% E85, the lambda is still 1, and it's still reported as 14.7 since it thinks it's gasoline, but the ACTUAL afr is 9.7:1 based on the increase in fuel required to keep lambda equal to 1.

[Ænema]

Originally Posted by V8bait

AFR is a calculated value from lambda.

O2 sensor does not know how much gas has been injected into the engine. O2 sensor does not know how much air was drawn into the engine. It only knows if the small sample it tastes is rich or lean, as measured from a stoichiometric ideal ratio of oxygen to fuel (aka lambda of 1)

I'll give you a quick example. The car reads the O2 sensors in lambda. When you are idling, lambda is 1. The DME will report this as 14.7 since it thinks you have gasoline. If you are running 100% E85, the lambda is still 1, and it's still reported as 14.7 since it thinks it's gasoline, but the ACTUAL afr is 9.7:1 based on the increase in fuel required to keep lambda equal to 1.

This guy needs to post more often...

[mrbillytalent]

I'm learning so much. Please don't stop. I had he same question with e85 afr's and what the logs show.

[AltecBX]

@V8bait Thanks for your input.

That's why I said it's open for discussion.

[V8bait]

I stole this from a cobalt forum with a quick search for you guys to mull over. Same as Altec posted but with some lambda's!


It's really not important what the reported AFR is, but to get the "true" AFR you would have to first convert the reported AFR to lambda, and then account for the ethanol concentration in the fuel, which can vary a lot from fill to fill.

As long as you are around a reported gasoline AFR of 12.5-13.2, your lambda is .85 to .9, which according to that chart puts you a little leaner than E85 peak power, but that's ok because you're not really on E85, you're on like E50. And ethanol doesn't react as poorly to lean mixes as gasoline anyway.

I post occasionally, waiting on a reply from VRSF. Seems like the drama has died down some here, we'll see.

[ksalih]

these are the posts that bring out the engineers, math majors and chemists.. I like when e90post has some worth while discussions from ppl who aren't here to troll. nice work OP

[akotten]

You really need to do some testing to find Least Rich Best Torque (LBT) for your given setup. With ethanol, it might be around 0.8 lambda, but with gasoline, it will be closer to 0.88 or so. Also, try not to get confused with the equivalence ratio either, which is 1/lambda.

Lambda:
X.X > 1 = Lean
X.X < 1 = Rich

Good fuel data here: http://ethanolpro.tripod.com/id213.html

[Mangler]

Originally Posted by V8bait

AFR is a calculated value from lambda.

O2 sensor does not know how much gas has been injected into the engine. O2 sensor does not know how much air was drawn into the engine. It only knows if the small sample it tastes is rich or lean, as measured from a stoichiometric ideal ratio of oxygen to fuel (aka lambda of 1)

I'll give you a quick example. The car reads the O2 sensors in lambda. When you are idling, lambda is 1. The DME will report this as 14.7 since it thinks you have gasoline. If you are running 100% E85, the lambda is still 1, and it's still reported as 14.7 since it thinks it's gasoline, but the ACTUAL afr is 9.7:1 based on the increase in fuel required to keep lambda equal to 1.

That's what I said but without all the needed reference information. I guess I need to elaborate more. Ha

T

[Dave W.]

Good stuff, just remember that the main flaw in the first post is that the OP assumed best power was made at stoich.

@altecBX How did you determine a ratio of 65/35 E85 to gas? Can you show your work?

[V8bait]

Originally Posted by Mangler

That's what I said but without all the needed reference information. I guess I need to elaborate more. Ha

T

I actually wrote that because I misread your post, had a quote in there too lol. I thought you were saying gas and E85 had the same AFR heh. I reread it and fixed it pretty quick though, no worries

Originally Posted by Dave W.

Good stuff, just remember that the main flaw in the first post is that the OP assumed best power was made at stoich.

@altecBX How did you determine a ratio of 65/35 E85 to gas? Can you show your work?

He was also flawed in the thought that you can up boost because less fuel is needed (he was confusing a lower afr to mean less fuel, in fact it means more fuel, if he wrote it out with some numbers he would understand). You can up the boost because the knock threshold is increased (higher octane, more latent heat, greater volume, etc etc). It was actually sort of confusing reading his post, because he knows you need upgraded fuel pumps (IE more volume), so I think he had just gotten a bit ahead of himself. No big deal, hopefully he has a little better visualization of what's going on now, and he's open to conversation about it is always nice

[N8N]

If you are going for max power, the more ethanol you can use the better. The only limiting factor is the flow rate of the fueling system.

[AltecBX]

Originally Posted by Dave W.

Good stuff, just remember that the main flaw in the first post is that the OP assumed best power was made at stoich.

@altecBX How did you determine a ratio of 65/35 E85 to gas? Can you show your work?

I described my steps in the first post.

Originally Posted by V8bait

I actually wrote that because I misread your post, had a quote in there too lol. I thought you were saying gas and E85 had the same AFR heh. I reread it and fixed it pretty quick though, no worries

He was also flawed in the thought that you can up boost because less fuel is needed (he was confusing a lower afr to mean less fuel, in fact it means more fuel, if he wrote it out with some numbers he would understand). You can up the boost because the knock threshold is increased (higher octane, more latent heat, greater volume, etc etc). It was actually sort of confusing reading his post, because he knows you need upgraded fuel pumps (IE more volume), so I think he had just gotten a bit ahead of himself. No big deal, hopefully he has a little better visualization of what's going on now, and he's open to conversation about it is always nice

Yes, what I meant to say was you can raise your boost because of the higher octane. Thanks for clarifying that up.

So let me get this straight.
To calculate lamba on Gas we divide our lean, rich, or stoich to get lamba (lean 12.5/14.7=0.850, rich 13.23/14.7=0.900, stoich 14.7/14.7=1)
And to get AFR on E85 we multiply (lean 0.867*9.765=8.466, rich 0.714*9.765=6.972, stoich 1*9.765=9.765)

Then what I have to find out is at what lamba are we making the best power to figure out how much E85 we need in our engine which I believe are running 10.2:1 compression ratio

[V8bait]

The math is strong with you, most people understand the concept but you get the mathematical relationship too. Anyway, yes you can do that, but I think you will find that the more e85 you can get, the better. It has to do with energy content of the fuel vs volume, and with ethanol, since you are also bringing oxygen, you can run richer than gasoline (the lambda readings). This means more relative fuel (adjusting for energy content volumes) will combust and find oxygen, meaning more energy can ultimately be released. Methanol has more power than ethanol, due to requiring even more volume than ethanol, meaning more oxygen, and more relative energy for that volume burned. Nitromethane (been using that example a lot lately) is the same idea, with two oxygen versus one in alcohols, for crazy power.

Gasoline has them beat on flame speed though.

[Joshboody]

This topic is prob over my head, but have a question...

supposedly rich mixture produces more energy (assuming perfect homogeneous mixture of course). BUT if stoich is using all the reactants how is this possible? Are there additional (or different) reactions? I do believe combustion is 2 stages and potentially a richer mixture allows more of the initial reaction which produces greater energy. Am I on the right track?