E85 Stoichiometric and o2 readings

[dumbricer]

I have a 1992 Eagle Talon TSi AWD with a 2.3L stroker motor running a 61mm turbocharger.

I am running E85 for fuel. Boost pressure is at 25PSI.

The car seems to run the best at 11.5 to 11.8:1 air/fuel ratio's. Stoichiometric of E85 is 9.7:1 or somewhere right around there.

According to a couple of websites I visited max power is achieved between 6.7 and 8.4:1 a/f ratios.

My question is: Is my car running extremely lean on E85 or is the sensor I am using not properly reading the A/F of E85? It is 11.5 to 11.8 to one on both a Innovate PLX wideband and a 3000 dollar Dynojet wideband kit.

The car is making 525whp and 446wtrq at 25lbs, so obviously power is there. No knock anywhere, and it has extremely conservative timing. Car runs extremely well and pulls extremely smoothly.

Is it lean or would I have to use a different gauge to read the A/F.

 

[boatmotorgod]

An o2 sensor compares the o2 content left in the tailpipe after combustion. The meter you are using is correlated to gasoline hence the air/fuel ratio it is reporting is higher than you expect. It is reporting a rich condition (very little o2) after combustion, so I would say you are OK. Though you dont know what the exact A/F number is. You could use an EGT to find out what number to expect on the gasoline callibrated o2 sensor, and then use that to dial in your setup.

 

[patprimmer]

All you need to do is correctly interpret your meter.

Think of it as using a metric rule to measure a 4" long object. The object is the same whether you call it 100mm or 4"

Stoich is stoich. If the scale calls it 14.7, it is a petrol rule, but for E85, if I take your word for it, it is 9.7:1, so scale reading of 14.7 = 9.7, therefore with any fuel, a reading of 11.65 on your gauge is 26% richer than stoich, or about A:f of about 7.2:1.


Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[NCShane]

The E85 has an oxygen component, so to get correct A/F ratios you need to compensate for this excess oxygen in the exhaust. Most good A/F or lambda meters (Horiba, ECM, etc.) allow you to adjust the fuel characteristics in terms of H:C, O:C, and N:C ratios. This way you can configure the sensor system for use with any fuel blend. If the meter you're using is not adjustable then you will be better off tuning with the lambda value, as it will give you a much closer number than A/F. You will still be off by 0.02 to 0.03 in my experience, but much closer than you are now.

 

[patprimmer]

There is no free oxygen in alcohol. It is already reacted, and therefore not available for further reaction. That is why you have a different a:f ratio.

All oxygen sensors only measure lambda. The gauge converts the lambda to a:f ratio. All you need to do is change the scale on the gauge.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Lou Scannon]

I will elaborate on patprimmers statement...
The sensors infer lambda, by sensing the relative concentration of oxygen in the sensor cell compared with ambient air. The well known NGK wideband oxygen sensors, when operating rich of stoichimetric, actually measure how much oxygen needs to be pumped into the sensor cell, in order to get a local stoichiometric mixture. From this they infer what stoichiometric ratio is present in the feedgas (e.g. exhaust). A similar process occurs in reverse, when operating lean of stoichiometric.

 

[EfiOz]

For this reason we never refer to AFR numbers, only ever lambda.