"May contain 10% Ethanol" - any way to know more in order to tune AFR?
 

Hello all

I am tuning with a wideband air fuel gauge which interprets Lambda into AFR but must be told what fuel you are burning in order to do so correctly. For instance there are settings for E85, Methanol, Diesel, etc.

Here in coastal CT every pump I am aware of says "may contain up to 10% ethanol". I am not asking if this is good or bad, I am asking if anyone knows with certainty that it typically DOES contain that 10%, and whether the content may differ by octane rating. There is a lot of fluffy internet posting and grousing about this but I am not able to find any information that feels trustworthy.

Alternatively:
I can (and have) set the gauge to read Lambda which eschews the issue of AFR as it is fuel independent. What I then need to educate myself on is what Lambda numbers correspond to good WOT, part throttle and lean cruise conditions.

I don't think it really matter the precise % added. all tat will do is skew the number you are looking for. if you choose regular petrol gas the stoich ration is 14.7:1 if you choose E85 is 9.73:1, but in each case lambda is 1. When you define the fuel type you are essentially choosing the scale for your displayed Air to fuel ratio. If you like thinking in terms of regular petrol gas with 14.7:1 for stoich and 12:1 for WOT. then just choose gas and tune by the numbers you know. in the end the tune should be good and AFR will be correct though not actually the displayed number.

This issue trips up a lot of people. Just set it to gas, and read it as if it were pure gas. Since the reading is lambda, but it converts the AFR to gas, you would consider a reading of 14.7 as stoichiometric, regardless of the fuel used or percent ethanol.

Wideband AFRs measure oxygen left after combustion so it doesn’t care about the fuel. You can interpret the numbers as if it were for pure gas for tuning and such. Although, in reality, the actual amount of fuel used is different than what the pure gas reading says. For example, while a 10% blend at stoich would show 14.7 in a gas scale, in actuality it is about 14.1 to 1.

0.85 lambda for boost/WOT, 1.0 part throttle / lean cruise should be uncontroversial and make good power.

With a real (programmable) EFI, knock detection and maybe a multi-fuel sensor with suitable trims, you can use higher lambdas on cruise if you felt inclined; 1.1, 1.15 isn't a problem for me.

It's actually quite easy to check the amount of ethanol in your gas, if you're curious ("up to 10%" isn't exactly specific - and the blend ratio as-delivered will vary between seasons, as ethanol runs poorly in winter). Folks with plastic fuel tanks (that react with ethanol and swell) are quite keen to know this...

Put some fuel in a measuring cylinder, add known quantity of water, it will settle to the bottom. Note position of the boundary line, shake thoroughly; ethanol will bond to the water (phase separation). Leave for 30 minutes, ethanol/water mix will separate out. Calculate how much ethanol was in the fuel from the new position of the boundary line.

E10 fuel is 14.1 Stoich.

Yes, you can make a difference adjusting your Lambda reference point by this number.