Stoich Calculator

[kritz]

Found this recently, fun with Excel.

https://www.google.com/url?sa=t&rct=...57155469,d.cWc

[atvfreek]

Here is some good info too as far as the tuning side of things

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.

[kritz]

I like this feature of it:

[nindoja]

@atvfreek; the numbers in this chart don't account for the variances in ethanol based on geographic location and season, so the specific gravity number is probably slightly off, right?

[kritz]

Need to get one of these soon.


Zeitronix ECA : SEMA Award Winning Ethanol Content Analyzer and Flex Fuel Sensor for E-85 and E-85/gasoline Blends

[atvfreek]

Originally Posted by nindoja @atvfreek; the numbers in this chart don't account for the variances in ethanol based on geographic location and season, so the specific gravity number is probably slightly off, right?

The specific gravity number won't be off. e10 is e10 and e15 is e15 etc. You just have to know what the ethanol content is and adjust that number in ATR as needed.

However small variances in ethanol content are only going to throw your LTFT/STFT off a touch. If it is beyond 10% off, then wot afr's will likely be off as well.

[nindoja]

Originally Posted by atvfreek The specific gravity number won't be off. e10 is e10 and e15 is e15 etc. You just have to know what the ethanol content is and adjust that number in ATR as needed. However small variances in ethanol content are only going to throw your LTFT/STFT off a touch. If it is beyond 10% off, then wot afr's will likely be off as well.

Good to know. Still trying to get a good grasp on e85. Off to do more reading.