Unleaded->Ethanol % Blend Tables

[MWPau]

Hi all,

So ive got good E85 ve/afr/ignition/boost tables.
Ive also got good Unleaded ve/afr/ignition/boost tables.

Now the question is, what should the flex % blend tables look like?
At the moment they are linear from 0% ethanol to 85% ethanol, which is wrong.

Ive come across the below graph which shows octane vs ethanol.
Should the ve/afr/ignition/boost blend tables pretty much follow the same curve?



Thanks

[nathaninwa]

I'd leave that to the dyno myself. My dyno shop says you can be full timing and boost around e60 and can get more aggressive starting around e40

[elutionsdesign]

Certainly the curve your car will like will be closer to those than a straight line, the dyno knows for sure.

[MWPau]

the dyno knows for sure.

How?
For example, at 40% ethanol, what should be the target AFRs?

[Laminar]

Stoich will always be 1.00 lambda. It's likely that your wideband measure lambda and converts it to an AFR output based on whatever fuel it's configured for. The wideband is told it's measuring gasoline, so it measures a lambda of 1.00 and outputs an AFR value of 14.7. If the wideband begins measuring E85, it will still see lambda of 1.00 at stoich, so it will output an AFR value of 14.7 even though stoich for E85 is more like 9.7. It may be more useful to set the wideband to display lambda so that you always have a common reference point.

[MWPau]

Forgive me if i sound rude... thankyou, but yes, all that is clear. The relationship between AFR and lambda is not what im asking about.

Im asking how much the ratio of ethanol to petrol changes the target AFR/lambda and VE.

For example, i currently have this which is linear (and wrong):

now.PNG

Im guessing it should look something like this?

maybe.PNG

[Laminar]

Ha! I gotcha now.

[elutionsdesign]

AFR isn't a good example of a blend table because the optimum lambda (what is actually being measured) won't change much if at all between E85 and petrol. Same with VE IF you are using the flex fuel sensor to read content and using the default settings to compensate, you may not be doing it that way although most probably will. But, boost and timing will be or can be significantly different, certainly with higher octane you can run more boost pressure at a similar ignition advance OR run more timing at a similar boost pressure, either way you're making more power. If I'm doing this I would decide ahead of time what I want my boost pressure to be at the various % ethanol points, set that, then go back and MBT calibrate timing at those points on the dyno. It is a lot of work but that's what it takes.

I had some COBB tuning training last summer and they had some interesting stuff with a GTR/flex fuel sensor. They found for that car anything above E70 was the same and it appeared pretty linear from E0-E70. Pretty cool they found a way to get the flex fuel sensor signal into the factory ECU and use it.

[MWPau]

My AFR tables are different for 0% and 85% ethanol. I run a bit leaner on E85 in a few places.
Table 1 is 0%, Table 2 is 85%.

afrs.PNG

I dont use the flex multipliers, as IMHO they are not accurate enough.

flexset.PNG