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Choosing the correct afr

EFI Tuning Fundamentals

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What is the afr at 1.0lamda please?

I'm responding here mostly to verify my own understanding of this.

Lambda 1.0 is a representation of stoichiometric afr. That is the ratio at which the oxygen in the air is perfectly matched to the fuel to

Completely burn all of the fuel/air mixture. It is therefore dependent on the specific fuel in question.

Assuming pump gas. Stoichiometric mixture = 14.7:1 = lambda 1.0

Jguysr you're bang on.

Nick, as Jguysr said it is fuel specific. Here are some common fuel AFR/Lambda Stoichiometeric ratios

Pump gas 14.7:1 = lambda 1

Ethanol 9:1 = lambda 1

E85 9.75:1= lambda 1

Methanol 6.42:1 = lambda 1

Diesel 14.6:1= lambda 1

This does also depending on how you're reading lambda 1. Most wideband controllers will not know what fuel you're running on and will assume its pump gas so lambda 1 will always relate to 14.7:1 . For example if you had e85 and had it at lambda 1 the wideband would say 14:7/1:00 but the engine would actually be 9.75:1. Hope that doesn't confuse you :)

As Chris has in his post, different fuels have different stoichiometeric AFR values, however the Lambda stoichiometeric value will stay at 1, this is why I prefer to operate in Lambda rather than AFR, as it is a fairly fuel agnostic value, and can't be misleading if the sensor is incorrectly configured.

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