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General E85, lambda, and target air fuel ratios

Posted by GST with PSI, Feb 10, 2017

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  1. GST with PSI

    GST with PSI DSM Wiseman

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    I've got into the habit of helping others with tuning, and as a result, have received may questions via PM asking for various advice. One of the reoccurring questions that seems to get asked is about target air fuel ratios, and how they relate to what your wideband O2 ultimately sees.

    When you're first introduced to them, these concepts can be confusing at first. I'm hoping to help others understand these concepts, as they are critical to understanding and targeting proper air fuel ratios while tuning.

    I'm going to break this down in what I believe is a simple way for most people to understand. This is by no means an all inclusive guide to these principals, nor do I claim to know the in-depth operational principals and engineering behind these systems. However, for the average Joe tuning their own car, this explanation should satisfy the basic knowledge required to be successful.




    Wideband O2 Sensors:

    Let's start with the wideband O2. Nowadays, few people tune without one, and for good reason. A wideband O2 sensor is probably one of the best tools to allow the user to determine how their engine is operating. As the name suggests, a wideband O2 (WBO2) sensor simply reacts to changing oxygen levels in the exhaust. The nuts and bolts operation of a wideband O2 can get fairly complex, but for the sake of this discussion, I'm going to keep this at a very basic level. If you would like to understand the details regarding WBO2 operation, you can do some searching on Google, or reference the links below:
    http://www.innovatemotorsports.com/resources/news3.php

    http://tayloredge.com/reference/Science/oxygensensor3.pdf

    https://www.turbobygarrett.com/turbobygarrett/airfuel_ratio_tuning_rich_vs_lean

    Now, there are some features of a WBO2 that set it apart for the typically narrow band sensors, but again, for simplicity's sake, just know that most WBO2 sensors very accurately determine air fuel ratio (AFR) by measuring oxygen in the exhaust stream (and as a result, unburned fuel as well). Depending on the ratio of oxygen and fuel detected in the exhaust stream, the O2 sensor outputs a voltage reading, which is then interpreted by some type of gauge or human readable system output (for example, ECMlink).




    Air Fuel Ratios:

    OK, so your WBO2 will tell you your air fuel ratio (AFR). So, what is AFR, and why does it matter? As the name implies, AFR is simply the ratio of air to fuel. We'll divide AFRs into 3 states:

    -Rich

    -Stoichiometric

    -Lean

    Given these 3 states, we'll start by talking about stoichiometric, since it's key to understanding the other 2 states.




    Stoichiometric:

    Stoichiometric air-fuel ratio is where the major byproducts of combustion (emissions) are at their combined lowest point. This means for a given fuel, you have the correct amount of air and fuel to produce a chemically complete combustion event. Put simply, if you burn all the air and fuel mix without too much of either left over (which in turn reduces emissions such as CO, NOx, etc.), your oxygen sensor will read stoichiometric. This air fuel mix that is chemically balanced is always referred to as stoichiometric, or stoich for short.

    Now, each fuel has its own stoichiometric air-fuel ratio. Here are some examples of fuels and typical stoich ratios for each:

    C16: 14.8:1
    Pump gas: 14.7:1
    Diesel: 14.6:1
    Q16: 13.6:1
    E85: 9.8:1
    Methanol: 6.4:1

    Given the known stoich value of a specific fuel, we can go back to our 3 states (rich, stoichiometric, lean)
    and determine which condition exists:

    Anything over stoich = lean

    Stoich = stoich (obviously)

    Anything under stoich = rich

    So, if we were tuning on pump gas (stoich is 14.7:1), a value of 9:0:1 would be rich. A value of 16.0:1 would be lean.




    Lambda:

    So, W T F is lambda? Lambda is another way of measuring air fuel ratio, and like stoichiometric, indicates AFR based on a standard reference point. So, let's break it down again into 3 states:


    -Rich

    -Lambda

    -Lean

    Now, here's where things can get confusing. The lambda value at the stoichiometric air fuel ratio for ANY fuel is always equal to a value of 1.00. The easiest way to understand this is to remember what the stoichiometric AFR actually is. Again, stoichiometric means for a given fuel, you have the correct amount of air and fuel to produce a chemically complete combustion event. So, no matter if you've got E85 or pump gas in the cylinder burning; if the ratio was such that all of the air and fuel were used up in the combustion process, your WBO2 will read stoich, or a value of 1.00 lambda. So once again, going back to our 3 states (rich, lambda, lean):

    Anything over lambda = lean

    Lambda (1.00) = stoich

    Anything under lambda = rich




    Lambda vs Stoichiometric:

    I like to think of lambda and stoichiometric ratios as two scales which essentially mean the same thing. In a nutshell, they both indicate AFRs. However, lambda is more universal in the sense that it's a constant regardless of the fuel being used. Meaning, if you're using your WBO2 and determine .80 is the optimal target AFR to make power for your application, you will be targeting a .80 AFR regardless of the fuel being used.

    If you consider how the lambda scale somewhat standardizes tuning, you wonder why lambda isn't used more often. Well, the answer is traditionally, most WBO2 sensor displays are calibrated to readout on a standard pump gas scale. Meaning, regardless of the fuel being used, at stoich/lambda, the gauge displays 14.7. Now, remember, stoich and lambda both just mean we got a chemically complete combustion event. Your wideband O2 sensor in the exhaust pipe doesn't care what fuel is being burned, it only cares how much oxygen is left over.

    So, let's say you decided to swap from pump gas to E85 one weekend. Let's also say your idle is dialed in great, and you're hitting a target AFR of 9.8:1 on E85. Since the O2 sensor simply reads the amount of oxygen in the exhaust stream, it's going to see a nice clean burn at 9.8:1 (stoich of E85), thereby producing a voltage that corresponds to stoich/lambda. The problem now comes when you're sitting in the drivers seat looking at your AFR gauge which is receiving that voltage reading. Remember, we have a gauge that's calibrated to read AFR on a pump gas scale. That means at stoich/lambda, the gauge will ALWAYS say 14.7:1, regardless of fuel. And, it also means your car that's now idling on E85 at 9.8:1 will actually read 14.7:1 on your gauge, since BOTH values are equal to stoich/lambda...So, now you know why you get guys using pump gas AFRs for different fuels, and why the lambda scale makes more sense when comparing fuels.

    The one important thing to keep in mind when referencing lambda is differences between various WBO2 setups. For example, if you're using an Innovate MTX-L, the lambda scale and gauge readout will always be the same regardless of the fuel used. However, if you switch to say, an AEM UEGO, the lambda scale and gauge readout will probably be slightly different than that of the Innovate MTX-L, as each manufacturer calibrates how their WBO2s interpret the voltages and data being received from the oxygen sensor, controllers, and other system hardware differently.

    Bottom line, if your gauge is calibrated to read lambda, stoich/lambda is always 1.00, and any value over or under is either lean or rich (respectively) regardless of the fuel used. There are formulas to figure out gauge conversions, lambda and various other things. I'm not going to cover them here, but they are easily found on the interwebs via a quick search of the function you're trying to perform. There are also some good examples here: http://www.dsmtuners.com/threads/what-is-lambda.228595/#post-50379068




    Wrapping Up:

    Again, I've tried to simplify the principals here to make sense to the vast majority of readers. Some of these principals can be explained much more in depth, but I've tried to present the fundamentals in order to appeal to the average dude, such as myself.

    For you visual learners, here's a great video that breaks these principals down as I've tried to outline above:
     
    Last edited: Feb 10, 2017

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  2. miliman13

    miliman13 Proven Member

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    I am the one who "knocks".... or Pm's LOL.
    I wanted to add since it was my curiosity and need for help that, in part lead to GST creating this thread.

    So if i have this correct.. this is how it goes.
    Lambda is the yield in calculation. [Actual/ theoretical]

    Gas stoichiometry 14.7/14.7 = 1 Wot 11.5/14.7= 0.78

    Ethanol stoichiometry 9.8/9.8 = 1 Wot 7.6/9.8 = 0.78

    So my self on a AEM eugo WB i can change the face plate and see Lambda units instead of AFR since its intended to be used with Pump gas.

    So GST, when you tune for 12.x:1 on WOT with E-85. those as in terms of " GAS " and not actual Ethanol ratios.
    Is this correct?

    Here is a good reference.. Cant believe its taken me so long to make sense of the sheet that came with my AEM so many yrs ago.

    http://www.schnitzracing.com/manuals/AEMWBK.pdf

    E85G.jpg

    93g.jpg It makes sense , comparing these two gauges the locations are equal to the Lambda scale.
     
    Last edited: Feb 10, 2017

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  3. miliman13

    miliman13 Proven Member

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    I also understand why you can lean out more with E85. Since its 85% ethanol Vs 10% ethanol (Gas)
    And proportionally the octane in gas is 91-93 Vs E85 being 100.
    The octane being the resistance to pre-detinaton or spontaneous combustion.
    And because its distilled it burns colder thus allowing more advance in timing = "mo fun"

    For gas i get that 11AFR at Wot is utilized to keep heat down.
    And any leaner is not good. Even though OEM is 9ishAFR

    So how does this collateral with ethanol.
    is 12AFR on gas scale the leanest you want before things get to hot?

    And at what point does e85 go from friend to foe. ?
     

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  4. bastarddsm

    bastarddsm Proven Member

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    The words "burns cooler" do not apply. The gas temperature in the cylinder are a function of AIT, and the amount of energy released (HP). The flame temp of ethanol might be different than that of gasoline, but that really isn't relevant here. E85 lowers EGT and combustion temps because it lowers AIT.

    Remember also, a wideband is a bit like trying to tell how much beer you drank last night by the color of your piss the next day. No matter what anyone says, a wide-band is not perfect, nor should it be the end all be all tool for tuning.
     

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  5. lasthope05

    lasthope05 Proven Member

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    Correct. You need one of these if you doing any kind of "real" tuning.

    https://www.amazon.com/gp/aw/d/B005...=UTF8&qid=1486818721&sr=8-2&keywords=otoscope
     
  6. Vegas smith

    Vegas smith Proven Member

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  7. lasthope05

    lasthope05 Proven Member

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    Yes. The magnification and light allows you to look down into the plugs easily.
     
  8. GST with PSI

    GST with PSI DSM Wiseman

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    Correct. This is AFR as it would be seen on a display calibrated for your typical pump gasoline.




    12.0:1 is simply the baseline I use when I start dialing in cars tuned on E85. There is no generic magic number that will keep you safe or make you the most power. Every setup is different, and is subject to different fueling requirements. Personally, I've always found 12.0:1 on E85 (pump gas scale) gives you plenty of cushion to play with the tune, while making good power overall. But here again, each application is different, and the tune (to include AFR) needs to be specifically tailored to the individual setup.

    This is exactly where @bastarddsm and @lasthope05 are exactly right in saying the WBO2 is not the end all be all for tuning. You need to take a holistic approach to tuning a car, and use as many methods to collect and interpret performance data as possible. Then using that data, make the appropriate adjustments to the tune and setup to optimize performance. Figuring out the best AFR is part of that process, and a WBO2 is simply a tool that helps you do it.
     

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  9. miliman13

    miliman13 Proven Member

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  10. miliman13

    miliman13 Proven Member

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    Do you mean as Air and fuel mix it lowers the temp.
    I can get that since alcohol is great for heat transfer.
     

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  11. Kapok6

    Kapok6 Proven Member

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    I can verify 12.0 does NOT work for all e85 cars. Lulz
     
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  12. miliman13

    miliman13 Proven Member

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    Care to elaborate?
     

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  13. Lester B

    Lester B Proven Member

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    I have an aem wb also. I just changed the knob in back to read lambda. Didn't change the face plate. And works perfect now.
     

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  14. Kapok6

    Kapok6 Proven Member

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    Sure. My current motor is 10.5:1 with GSC S2's and a DSM82 HTA and it doesn't like any leaner than 9.5ish around peak torque and no leaner than low 10's after peak torque or it knocks. Those afr values are on a gas scale.

    11.5-12 was good on my older lower compression motor with less aggressive cams. No-go on this motor.
     
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  15. miliman13

    miliman13 Proven Member

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    To which setting?
    8755.JPG 855.JPG

    P1 : is X=Y
    The only Lambda appearing one is P4, But the volts are more of a Narrow band.
    I believe in on P1.
     

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  16. GST with PSI

    GST with PSI DSM Wiseman

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    I wouldn't say most E85 is E70. Most of the fuels I've tested were E85 or better. Even the winter blends here are around E80.

    Here again, there's no magical number for ethanol content. Each application will have different requirements regarding fuel grades, and to add to that, each grade of fuel can vary greatly depending on the quality. You could get E85 out of a dirty old storage tank from a blender pump and it be complete sh**. Alternatively, you could get high quality E50 from the station next door and make better power without knock. The only real way I've found for the average guy like myself to gauge the fuel quality is:

    1) Test the ethanol content
    2) See how it performs in the car
    3) Inspect the injectors for goo
    4) Use stations with modern pumps that service a fair amount of E85 customers (this ensures the fuel is getting used and replenished, not sitting in a crusty ass tank for years on end.)

    From personal experience, I have not seen any difference in how my car performs on fuels with lower ethanol content (I'd say E60 and up, since I've never personally ran anything below that). The batch I dyno'd the car on was around E70. Reading I've done backs up my real world observations, but that only holds true for me. As I said before, each application is different, and each setup will have different requirements. I bet my ass if you tune @Kapok6's high compression motor on E85, then dump a tank of E50 in it, you'll probably see poor results, or potentially even damage something. Some cars that are running closer to the knife's edge can't afford a drop in octane even a few points. Being able to think through this kind stuff is what separates the guys making serious power from the ones blowing $hit up. I'm currently neither of these, which I'm fine with ;)
     

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  17. miliman13

    miliman13 Proven Member

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