AFR Gasoline - E10 Wide Band 02 sensor tuning using Lambda

[EagleMark]

The term Stoichiometric ratio describes the chemically correct air-fuel ratio necessary to achieve complete combustion of the fuel. It is represented by the Greek letter, lambda.

The exhaust gas oxygen sensor is also called the lambda sensor, since it can be used to maintain the air-fuel ratio at lambda equal to 1, within very close limits. It can be installed in the exhaust manifold, where it measures the percentage of oxygen in the exhaust gases.

1.00 is Stoich
.99 is rich
1.01 is lean
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First a couple of misconceptions. Narrow band O2 sensors do not adjust to 14.7 AFR and Catalytic convertors do not work best at 14.7 AFR. The narrow band O2 sensor adjusts to Stoichiometric of fuel and Cats work best at Stoich.

The 14.7 AFR was correct, but it is calculated at Stoich.
Stoich = Lambda
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Stoich for gas is 14.7 AFR. Stoich for Ethanol is ~9.00AFR. That means that Stoich for E10 would be (14.7 x 0.90) + (9.00 x 0.10) = 14.13AFR.

Now the confusion on tuning by AFR instead of Lambda. WOT for 12.78 AFR or 0.87 lambda (0.87 = x / 14.7 AFR so x= 12.78AFR) at WOT. That's for gasoline, not E10. E10 requires lower AFR as seen in the example above. For E10, it would be 12.2AFR (14.1 x 0.87 = 12.2).

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A Wide-Band is not an AFR gauge. It is a Lambda gauge.

Most Wide Band controllers calculate AFR based of Lambda to give user a number he wants to see...

E10 Stoich is 14.1 -- Lambda for E10 = 1.0
E0 Stoich is 14.7 -- Lambda for E0 = 1.0
Notice Lambda is always 1.0 when adjusted by narrow band O2 sensor?

I typical Wide-Band Gauge is programmed to display 14.7 at 1.0 Lambda. So AFR is not accurate with E10 fuel, at cruise or at WOT PE!

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Found this post from Greg Banish and found it interesting.

To work effectively with Ethanol blends, you really need to switch to units of Lambda to avoid confusion. (lambda = AFR/stoichAFR)

Almost any hydrocarbon fuel makes peak torque somewhere near lambda=0.9. For pure gasoline this is an actual AFR of (14.68)*(0.9)=13.2 AFR. With e10, it would be calculated based on lambda with a different stoich point: (14.13)*(0.9)=12.7 AFR. Both mixtures, although numerically different, look the same to the combustion process.

e10 isn't a huge difference, but e85 get much more significant: (9.85 stoich)*(0.9)=8.9 AFR, which still looks the same as 13.2 with gasoline as far as the combustion process is concerned.

Wideband sensors also don't know what %ethanol blend you're burning. The UEGO (wideband) sensor just measures oxygen percent and delivers a lambda number. The cheaper widebands just multiply this measured lambda by 14.6 to give inexperienced users a number they're used to seeing in magazines. Don't tune to AFRs (instead of lambda) using ethanol blends, it will only mislead you.
__________________
Greg Banish
Calibrated Success, Inc.

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=4399&stc=1&d=1364793887

[91ss]

Stoich for gas is 14.7 AFR. Stoich for Ethanol is ~9.00AFR. That means that Stoich for E10 would be (14.7 x 0.90) + (9.00 x 0.10) = 14.13AFR.

Now the confusion on tuning by AFR instead of Lambda. WOT for 12.78 AFR or 0.87 lambda (0.87 = x / 14.7 AFR so x= 12.78AFR) at WOT. That's for gasoline, not E10. E10 requires lower AFR as seen in the example above. For E10, it would be 12.2AFR (14.1 x 0.87 = 12.2).

Just to add some. This is all true. But, while ACTUAL AFR is not correct for say E10, you can still use AFR, if you're comfortable in AFR.

If the WB displays 12.78, the ACTUAL AFR will be 12.2. So you don't really have to switch to Lambda. And then, just like tuning for most power, fastest acceleration, you're going to have to find the best AFR regardless. E10 may not perform best with a lambda of .78 anyway. It may like .79, it may like .77 for your combo.

The problem arises if the guy is trying to get the WB to read 12.2 because he thinks he has E10. Which may not be exactly that either.

[RobertISaar]

little adjustment to the comment about the cat:

the cat works best NEAR stoich.... ideally, you would run the engine at stoich, then every once in a while(by this, i mean a pretty short term) send it slightly lean, since the cat NEEDS free oxygen to do some of it's work. alternatively, you could jump pump AIR directly to the cat at all times(until it gets too hot), that will keep your O2 sensor happy(and accurate) while keeping the cat supplied with the components it needs to catalyze the exhaust gasses.

the compromise to this is the path most automakers took and send the engine slightly rich and slightly lean alternatively using the narrowband for feedback. it's not a perfect system, but it does work pretty well.

[daleulan]

little adjustment to the comment about the cat:

the cat works best NEAR stoich.... ideally, you would run the engine at stoich, then every once in a while(by this, i mean a pretty short term) send it slightly lean, since the cat NEEDS free oxygen to do some of it's work. alternatively, you could jump pump AIR directly to the cat at all times(until it gets too hot), that will keep your O2 sensor happy(and accurate) while keeping the cat supplied with the components it needs to catalyze the exhaust gasses.

the compromise to this is the path most automakers took and send the engine slightly rich and slightly lean alternatively using the narrowband for feedback. it's not a perfect system, but it does work pretty well.

Most modern cats run with postcatalyst sensor feedback as well but with a switching sensor in the front. Depending on the formulation the catalyst may want to have a lean bias or a rich bias but when you add the postcatalyst sensor that can be adjusted automatically so as the catalyst and oxygen sensor ages the actual lambda that the catalyst sees does not change away from best conversion. I do my ECM software using lambda as a reference (it makes the math easy when the fuel composition changes), I end up calibrating the front O2 sensor for a target lambda (not voltage like the 1980's and 1990's GM software seems to use) and usually the target is actually slightly rich for better NOx conversion at the expense of CO - a typical target for me is about 0.988 to 0.998 lambda depending on the catalyst. The problem with a front-sensor system is that the front sensor has a tolerance of about 0.02 lambda with age (for a Bosch LSF4.2, anyways) and if you can keep tighter than that you can improve conversion efficiency a lot - I have seen NOx emissions on a ETC (european transient cycle) drop an order of magnitude (from 4 g/kWh to 0.4 g/kWh) just by turning on the postcatalyst sensor. The tolerance of that same oxygen sensor after the catalyst is about 0.0005 lambda. The front switching tends to store and release oxygen in the ceria and zirconia OSC components and after the reactions in the catalyst the exhaust gas is pretty empty of oxygen which makes the postcat O2 sensor very sensitive. A typical target for gasoline is a postcatalyst voltage of between 0.48 and 0.62 volts depending on the NOx requirement. When running with a UEGO most (but not all) catalysts want some dithering of air-fuel ratio; there do exist a few catalysts without much oxygen storage capabilities that want a perfectly stoichiometric mixture. A catalyst with a monster-sized oxygen storage capability is quite difficult to control due to time delays, there are ways of doing it but those are mostly trade secrets.

Another odd duck is the non-PGM catalysts (base metal cats) that use copper and other materials like that. The feedback algorithm is totally martian on those catalysts but they must be used with extremely low-sulphur fuels.

[daleulan]

I forgot to mention that most cats I have worked with want a dithering of about 0.02 to 0.08 lambda (peak-to-peak), mostly around 0.05 lambda. That dithering can be 'forced' like you would do on a UEGO or the result of the natural limit cycle on a switching sensor.

[EagleMark]

Another bigger issue is a lot of gauges can't be set to Lambda or if your using E fuel which most of us are unless your going out of your way for Non Ethanol or race fuel is:

1. Did you set Stoich or desired AFR in calibration to 14.13?
2. Did you set up the Wide Band Controller to 14.13?
3. Did you get the correct voltages for AD outputs to do conversion in data logger/adx files? Not needed if your run Serial WB to EFI Live V2...

If everything is set to 14.7 and your using fuel that is 14.1? Then your off by .6! You won't know it though because the Wide Band controller is not a wide band controller, it's a Lambda controller. It converts Lambda to AFR because that's what humans want to see. If your in Closed Loop the narrow band O2 sensor is adjusting to Stoich of fuel, Lambda/WB controller is reading stoich/lambda, so the only thing off is your INT/STFT and BLM/LTFT... if you want to get fuel trims close to 0? You have to set everything up right from AFR in bin/calibration and WB/Lambda controller. There's nothing like doing a tune in Open Loop via WB, then going Closed Loop and fuel trims are way off!

[streetperf]

EagleMark,

thanks for all information on E10 and a wide band. I'll have to do some adjusting on my 98 vortec 383. As you stated in one of the threads you don't know the amount of ethanol in your fuel each fill up. Also you don't know where the sweet spot is for your combination.
Again thanks for the info

[delcowizzid]

i tune all fuels with my wideband set as per petrol its just easier.as said above it converts lamda to a/f ratio so the displayed ratio should remain correct.

[RobertISaar]

as long as you understand that 14.7:1 on the controller/display doesn't necessarily mean 14.7:1 to the engine, it's not really a problem. could run straight ethanol and have target AFRs in the 9s in the calibration and 14.7:1 on the display will still mean you're running stoich.

i would prefer for instrumentation to match reality, whenever possible to do so.

[EagleMark]

Lambda is always accurate with any fuel. Bonus to using Lambda data in history tables is it is your multiplier!

[EagleMark]

2014 LT1 Direct Injection Corvette is first GM to come from factory with 14.1 AFR as Stoich!

[RobertISaar]

is there an article from GM or something along the lines? or just someone took apart a factory BIN to find it?

[EagleMark]

Factory bin.

[RobertISaar]

i see the thread now.

i think i need a better source of income so that i can bribe GM engineers for the calibration decode. :laugh:

[Caleditor]

GM has been using these RPO codes for years and a few more


FHO

Vehicle Fuel Gasoline E10



FHS

Vehicle Fuel - Gasoline E85





One thing to remember the PCM uses the O2 sensor as a tool. The PCM drive the O2 sensor voltage to a set parameter and the drives it back the other way. The PCM drives the O2's with the injectors. Try swapping the O2 leads from side to side and then think about it. You will find the engine will surge and the fuel trims will not be the same. If the O2 sensor is mounted too far away the PCM will get out of sync because of the added duration it takes for the PCM to see the target voltage