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# AFR for different ethanol blend

### Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

Since pump 93 contains roughly 10% ethanol content and AFR for pure gasoline is 14.7, is the actual AFR slightly richer than 14.7 even though the gauge says 14.7 because of added ethanol content?

We know pure gasoline is 14.7 and E85 is 9.8, is there a way or formula to calculate AFR for any blend like E30?

I understand using Lambda is the best way to tune multiple fuels and aiming for the same gauge displayed AFR will get the right results, but just curious how to get the correct AFR for each blend on paper.

I tried to calculate by adding the two fuels by percentage for E85: (0.85x9.8)+(0.15x14.7)=10.5 which is leaner than 9.8 so it must be wrong.

Lambda 1 is always stoichiometric ratio for any fuel, is there a scientific scale for WOT operation with different blend or is the difference so small that we can ignore and just use common Lambda values for all fuels?

Sorry if everything above is explained in future courses, I just started with the basic course and this has been bugging me.

What is wrong with 10.5 being leaner than 9.8?

The calculation method is wrong- not the "10.5 being leaner than 9.8" part.

What makes you think that calculation is wrong?

The method- not calculation itself. For E85 it should be 9.8 instead of 10.5- since the calculation is right, my method must be wrong.

Stoich for 100 percent pure ethanol is 9.8. Stoich for gasoline is 14.7. Stoich for 85 percent ethanol and 15 percent gasoline will be 10.5... I don't see anything wrong in this calculation...

Hmmmm…. Isn’t E85 9.7 and pure ethanol is 9? You’re confusing me, if I’m wrong I apologize for the confusion.

Sorry. I made mistake. Indeed it is 9, 14.7 and 9.8 for E85 mix. But I still don't get it what made you confused...

By my method of calculation I got 10.5 for E85 whereas in reality it’s 9.7, and I still don’t know how to get value for E30.

Take 85 percent times 9 for ethanol

Take 15 percent times 14.7 for gasoline

Add it together and you'll get 9.8 for E85.

Now take 30 percent times 9 for ethanol

Take 70 percent times 14.7 for gasoline

Add it up and you'll get 12.99 for E30

I see where I did wrong… thanks.

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