For those running E85...AFR question
03-09-2009, 08:40 AM
#4
I found this on another forum. It's helped me get full understanding to finish my e85 tune.
"Understanding Air/Fuel ratios
This article assumes you already understand the concept of the air/fuel ratio (AFR), but if not, familiarize yourself by visiting this Wikipedia link. You may have already read that E85 has a different stoichometric air fuel ratio than gasoline's 14.7. The stoich AFR for E85 (at 85% Ethanol) is 9.76. The stoich value represents an ideal perfect burn of the fuel usually used at part throttle conditions. Full throttle conditions require a richer mixture than stoich to prevent the dreaded detonation, or pinging.
However most AFR gauges you can purchase to display a numerical value of the AFR, are showing you values for gasoline. This is where it can get tricky, and it's important to understand how this ratio works on both gasoline and ethanol-based fuel.
All AFR's regardless of fuel type work off of a common number called Lambda. A value of 1.0 in Lambda represents the stoich for any fuel. Gasoline is Lambda 1.0 at stoich. E85 is Lambda 1.0 at stoich.
If you already have a standard gasoline AFR meter hooked to a wideband O2 sensor, you can still use the displayed gasoline AFRs in determining your engine's true AFR. For example, if your gasoline meter is showing 14.7, then we know this is Lamda of 1.0. The equivelent on the E85 side is around 9.7. Therefore you can conclude that the 14.7 you see on the gauge is a true AFR of 9.7. This allows you to effectively use existing gasoline AFR components or software to tune an E85 Mustang without buying special equipment. Simply use the same target AFRs on your gasoline gauge that you normally targeted for gasolline. "
"Understanding Air/Fuel ratios
This article assumes you already understand the concept of the air/fuel ratio (AFR), but if not, familiarize yourself by visiting this Wikipedia link. You may have already read that E85 has a different stoichometric air fuel ratio than gasoline's 14.7. The stoich AFR for E85 (at 85% Ethanol) is 9.76. The stoich value represents an ideal perfect burn of the fuel usually used at part throttle conditions. Full throttle conditions require a richer mixture than stoich to prevent the dreaded detonation, or pinging.
However most AFR gauges you can purchase to display a numerical value of the AFR, are showing you values for gasoline. This is where it can get tricky, and it's important to understand how this ratio works on both gasoline and ethanol-based fuel.
All AFR's regardless of fuel type work off of a common number called Lambda. A value of 1.0 in Lambda represents the stoich for any fuel. Gasoline is Lambda 1.0 at stoich. E85 is Lambda 1.0 at stoich.
If you already have a standard gasoline AFR meter hooked to a wideband O2 sensor, you can still use the displayed gasoline AFRs in determining your engine's true AFR. For example, if your gasoline meter is showing 14.7, then we know this is Lamda of 1.0. The equivelent on the E85 side is around 9.7. Therefore you can conclude that the 14.7 you see on the gauge is a true AFR of 9.7. This allows you to effectively use existing gasoline AFR components or software to tune an E85 Mustang without buying special equipment. Simply use the same target AFRs on your gasoline gauge that you normally targeted for gasolline. "
