Equivalence Ratio from Wideband?
 

I have an AEM wideband with lambda vs. voltage shown in this table...

Attachment 114994

Can I use this lambda to calculate equivalence ratio even though the stoichiometric ratio of my fuel is less than that of gasoline? I'm assuming a stoich AFR of 14.17 for gas with some ethanol content. The equation for EQR is...

WB_EQR = 1 / WB_lambda

But can I use the lambda that comes from the lambda vs. voltage curve in Table 3?

Then to calculate the correction factor I'm using this equation...

BEN = GM.EQUIVRATIO * WB_lambda

The issue I'm having is that my cruise AFR is around 14.9 despite the BEN factor being basically 1.0. I'm using the AFR vs. voltage curve also shown above. Is this correct?

Follow up question/thoughts...

Is it correct to assume that lambda outputted from the wideband is independent of fuel type. As in, if the wideband is outputting a lambda of 1.0 when burning gasoline then it's at stoich AFR of 14.7, and if the wideband is outputting a lambda of 1.0 when burning E85 then it's at stoich AFR of 9.7?

I'm thinking the AFR vs. voltage curve shown in the table is for gasoline only. I would need to modify the curve for my lower stoich value of 14.17.

Long story short, I think the BEN's are correct but I'm not calculating the correct AFR.

Anyone agree?

A wideband does not know the difference between fuels. An oxygen sensor reads oxygen in the exhaust system. Straight ethanol mixed at a perfect ratio is 1.00 lambda, and gasoline mixed at a perfect ratio is 1.00. You would need to change the ratio when programming the wideband to changw the output displayed in AFR to match your fuel.

Log in lambda, and multiply by the lamdba ratio to adjust your map. So if your lambda is 1.05, and you multiply that cell by 1.05 the fuel should come out perfect. I usually do this a few times to get it perfect while smothing the cells so the map doesnt have any abrupt spikes.

Thanks! I think my expression for AFR is incorrect then. I'll just calculate AFR from lamdba instead of from the wideband voltage.

AFR has pretty much followed the old gas at 14.68. Most people just leave their sensor at that even though they are running e10 as they are more familiar with those numbers. E10 is about 14.17 actual AFR.

I changed it so WB_AFR = WB_lambda * stoich AFR. Now it's reading what it should be. Thanks for the clear explanation.