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Old 11-26-2006, 01:30 PM   #1
PeteDucati
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Default Targe A/F ratio with pure methanol.

Out of curiosity, what's an appropriate air/fuel ratio (as read by a wide band) for a car running 93 octane and pure methanol? I hear numbers ranging from 11:1 all the way to 12.5:1 - I'm assuming the wideband would be calibrated for a gas engine (read a thread somewhere about recalibration needed for *true* a/f readings).

I don't want to "wash out" the cylinders.
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Old 11-26-2006, 02:53 PM   #2
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There is no appropriate a/f ratio. The ratio you choose to run should depend on many things. For what it's worth though, I've heard that you should be able to make more power with a reading(on a wbo2 sensor calibrated for petrol) of 12-13.5 to 1 then with a reading of richer then 12 to 1. This would mean that running a richer reading(then 12 to 1) should make the chance of cylinder wash higher, and not help performance.

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Old 11-26-2006, 04:34 PM   #3
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Thanks Hippy.. obviously the more methanol I inject the leaner I can safely run- correct?
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Old 11-26-2006, 04:55 PM   #4
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The meth will affect your a/f reading, if your wb is currently set to read for gasoline it will be hard to determine what a "safe" reading is.

If your WB is capable of showing you readings in lambda instead of A/F you can make things much easier on yourself and not have to worry about calculating the appropriate a/f based on how much meth your adding at that exact moment.

This is a writeup that a member on another board did when the topic of different wb's came up.


Quote:
You can't just plug in a wideband into the exhaust, power it up and get a voltage to compute to A/F. Much more complex. It requires a heater control circuit to hold the sensor head at a constant temperature so accuracy doesn't shift. A wideband O2 sensor also has what is essentially a narrowband sensor (Nernst cell) that can only accurately measure A/F at 14.7:1 (450mV). In order to figure out what the A/F is at other times there's also a pump cell that moves oxygen ions into and out of the Nernst cell. This requires a controller as well. How much oxygen that has to be added or removed to hold the Nernst cell at 14.7:1 (where it's accurately measuring) is then used to calculate Lambda.

Oh yeah, widebands don't measure A/F. They measure Lambda which you can think of as the optimal or near complete burn of fuel where all air (oxygen) gets used to burn all fuel, which happens to be optimal for emissions and combustion. That point is called stoichiometric or simply "stoich".

So a wideband can measure Lambda. Lambda of 1 is always equal to stoich, but stoich varies by the fuel type. Regular 100% gasoline has a stoich point of 14.7:1 while ethanol is around ~9:1. Most of the widebands measure Lambda and then compute the A/F using the stoich point of gasoline (14.7:1). If the wideband measures a Lambda of .85 it is equal to 85% of 14.7, which the wideband controller computes (.85 x 14.7) to give you a displayed A/F ratio of ~12.5:1.

Now most widebands are always preset to use the stoich of pure gas which is 14.7:1, but oxygenates added to fuel for emissions (such as ethanol) or injecting methanol in a water injection system will alter the proportion or ratio of fuel being burned in the combustion chamber. And remember that different fuels have a different stoich, so the average stoich of the overall air/fuel mixture being burnt can change (might be 14.5:1, 13.9:1, etc.).

Optimal emissions is a Lambda of 1 and optimal power is generally between .75-.85 depending on a lot of factors such as the efficiency of the engine and the parts attached to it. On pure gas .75-.85 Lambda equals about 11:1 to 12.5:1 (.75 x 14.7 and .85 x 14.7). That's what most people will tell you tune for. But if you live in an emission control state that has 5 or 10% ethanol in your gas at the pump it will alter the stoich. Let's say the stoich of your fuel is 14.3:1. That would make that .75-.85 optimal range compute to an A/F ratio of 10.75 to 12.15 (.75 x 14.3 and .85 x 14.3), so if you tuned for 12.5:1 because someone on pure gas said it was safe you would actually be running lean for your fuel. So you can't exactly compare A/F ratio's to someone else in another state that has a different blend. Remember almost all widebands compute A/F at a set 14.7:1 point and that might not be the actual stoich of the fuel you are running.

The Innovate widebands can display in Lambda so you can just tune off that and completely skip having to deal with A/F ratio. Say optimal power is a Lambda of .80 on your car. It wouldn't matter what fuel you burn or inject since the wideband is displaying Lambda directly with no calculations "assuming" the fuel type to give you an AFR. So above .80 Lambda is lean and lower is richer.

By the way you can also change the fuel type programming on the Innovate widebands to correspond with the fuel you're running. That means if you were using pure ethanol (stoich of 9:1) you could tell the wideband to use that 9:1 instead of 14.7 to display the A/F ratio. So .80 Lambda would display as 7.2:1 if the Innovate was set up to use stoich of ethanol (.80 x 9) or as 11.7:1 if set up for the stoich of gasoline (.80 x 14.7). That's how all other widebands will work. The tricky part is when you start mixing ethanol and gas and don't know the exact stoich point. But why even bother trying to figure that out and then figuring out what your wideband should be displaying for a safe AFR when you can just use Lambda?


Back to your previous post, if you want to just take the voltage off a Bosch LSU4 stuck into the exhaust it isn't going to happen. But the wideband controller does usually output a wideband signal (0-5V scale) and most also offer a simulated narrowband output (0-1V, .45V switching point). And the scales for those common wideband controller output's are out there (and on the Innovate's you can alter that scale in the firmware to suite your needs), so you could take that 0-5V scale, create a circuit, and then output to a bar graph, your own numeric display, etc.

That should be enough info to get you started? I've got the longer version from another post saved somewhere.
The aem I'm using as well as a few others can display in lambda and when I get my WI installed over the winter I intend to switch mine over to read in lambda.
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Old 11-26-2006, 05:15 PM   #5
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So, how does someone (my tuner) properly "tune" for methanol injection if the wide band readings are bunk? Is it one of those deals where you set up timing to something conservative and start pulling fuel, check EGTs, and look at the dyno plots for gains?
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Old 11-26-2006, 06:53 PM   #6
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Quote:
Originally Posted by PeteDucati View Post
Thanks Hippy.. obviously the more methanol I inject the leaner I can safely run- correct?
It's more like the higher percent of meth to 93 octane petrol, the leaner you can run. This is cause running higher percents of meth to petrol will raise the octane more then running lower percents. At the same time, the less petrol you run, the more alc you can run without having a greater chance of cylinder wash/misfire and things of that sort. It's upto you to find the right mix for you. As a rule of thumb though, I inject the same amount or less liquid then the amount of petrol I remove. Ie- My air/liquid ratio with injection ends up being the same or leaner then it was b4 injection. Here are a few examples, but note that the air/liquid and air/fuel ratios will be the same since there's no water being injected....

Code:
air/petrol ratio           alc/petrol %         a/f reading     a/f ratio           octane equivilent...
11 to 1                     0%                         11               11                   93
12.5                        10%                        11.7(ish)       11.4                95.3
13                           15%                        11.5(ish)       11.3               96.55
13.5                         20%                        11.6(ish)       11.3               97.6
14                            25%                        11.8(ish)       11.2               98.75...
...                                                          ^edite
...                                                           values in "a/f reading" column are just hypothetical:)
...
No matter how rich the a/f ratio, % meth to petrol is what dictates how high the octane goes up. There's also a higher percent of meth to petrol with a given amount of meth when less petrol is used......

Quote:
Originally Posted by TurboGLH View Post
The meth will affect your a/f reading, if your wb is currently set to read for gasoline it will be hard to determine what a "safe" reading is.....
I don't agree with this, or with the quote you posted. The quote says that a wbo2 sensor measures lambda. They obviously can't and don't measure lambda, since there is no lambda in exhaust gasses, and they're not called lambda sensors. Wideband oxygen sensors are used to detect the oxygen content in the exhaust gasses. Lambda is the scale that is used to report the amount of oxygen content in a way that doesn't directly relate to a/f ratio, because people don't always use the same fuel. This doesn't mean that you need to see the lambda or recalibrate your wbo2 sensor just cause you're using a new fuel or mixing fuels. This is because of a few things. First would be that the reading a wbo2 unit gives will always relate to the same lambda. Ie- a reading of x on the unit will always be a lambda of y no matter what fuel is being used. At the same time, recalibrating the wbo2 unit for injection is not easy or even possible in most cases because it doesn't know the % meth/petrol at all times, and people don't run alc all the time. The wbo2 unit would actually have to measure the amount of petrol and meth to do this, and it obviously doesn't work like that. Course, this is all just my opinion......

peace

Last edited by hippy; 11-28-2006 at 02:42 AM.
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Old 11-28-2006, 01:10 AM   #7
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Quote:
Originally Posted by hippy View Post
It's more like the higher percent of meth to 93 octane petrol, the leaner you can run. This is cause running higher percents of meth to petrol will raise the octane more then running lower percents. At the same time, the less petrol you run, the more alc you can run without having a greater chance of cylinder wash/misfire and things of that sort. It's upto you to find the right mix for you. As a rule of thumb though, I inject the same amount or less liquid then the amount of petrol I remove. Ie- My air/liquid ratio with injection ends up being the same or leaner then it was b4 injection. Here are a few examples, but note that the air/liquid and air/fuel ratios will be the same since there's no water being injected....

Code:
air/petrol ratio           alc/petrol %         a/f reading     a/f ratio           octane equivilent...
11 to 1                     0%                         11               11                   93
12.5                        10%                        12.2(ish)       11.4                95.3
13                           15%                        12.5(ish)       11.3               96.55
13.5                         20%                        12.6(ish)       11.3               97.6
14                            25%                        12.8(ish)       11.2               98.75...
...
...
...
No matter how rich the a/f ratio, % meth to petrol is what dictates how high the octane goes up. There's also a higher percent of meth to petrol with a given amount of meth when less petrol is used......



I don't agree with this, or with the quote you posted. The quote says that a wbo2 sensor measures lambda. They obviously can't and don't measure lambda, since there is no lambda in exhaust gasses, and they're not called lambda sensors. Wideband oxygen sensors are used to detect the oxygen content in the exhaust gasses. Lambda is the scale that is used to report the amount of oxygen content in a way that doesn't directly relate to a/f ratio, because people don't always use the same fuel. This doesn't mean that you need to see the lambda or recalibrate your wbo2 sensor just cause you're using a new fuel or mixing fuels. This is because of a few things. First would be that the reading a wbo2 unit gives will always relate to the same lambda. Ie- a reading of x on the unit will always be a lambda of y no matter what fuel is being used. At the same time, recalibrating the wbo2 unit for injection is not easy or even possible in most cases because it doesn't know the % meth/petrol at all times, and people don't run alc all the time. The wbo2 unit would actually have to measure the amount of petrol and meth to do this, and it obviously doesn't work like that. Course, this is all just my opinion......

peace
Your answer is confusing to me, you obviously understand what lambda is and how it relates to each fuel type (ie the same no matter what the fuel) but you start out by saying that a wideband doesn't measure lambda, which it most certainly does. The controller does the conversion to a/f based on the fuel type. Most simply offer gas or straight lambda readings, but I believe that innovate offers conversions for different fuel types.

Instead instead of using your chart above to figure out the "correct" a/f ratio, try this. You determine what a/f you would want to run on gas alone (say 11.5) divide 14.7 by your goal of 11.5 and you get the appropriate lambda reading (0.78). Now simply tune to that, regardless of how much meth your adding vs gas. You can add more meth and less gas to control knock as needed, but you will always be able to look at your gauge and know your at the right zone a/f wise regardless of the mix your running.
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Old 11-28-2006, 02:06 AM   #8
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You can put water in a cup, and it's a cup of water. You can't put lambda in a cup, because lambda is the cup. Oxygen is the water. This is what I was trying to say. Lambda is a unit of measurement, not the thing which is being measured. It's like an inch, or a yard. "An inch or yard of what?" Exactly....

On the note of tuning to lambda, why figure out what lambda is? You're telling him to tune to a reading of 11.5, but in terms of lambda. Why not just tell him to tune to a reading of 11.5? It's like you think that converting the reading to lambda magically changes something. Shooting for a lambda of .78 isn't gonna make the a/f ratio any more "correct" then shooting for a reading of 11.5 because they're the same thing. It's like telling somone to put his brick onto a scale that shows a reading of kilos instead of pounds. The brick will most likely weigh the same on both scales<wink>.

The chart I put up above was not to show him the correct a/f ratio to run, since I don't think there is a correct a/f ratio to run. The chart was an effort to show the different mixes, resulting octane, and how to avoid running richer then without injection. If he ran 11.5 b4 injection, and tuned for that reading with meth, his a/f ratio would get richer. The more meth he used, the richer the a/f ratio would be......

peace

Last edited by hippy; 11-28-2006 at 02:44 AM.
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Old 12-07-2006, 12:07 AM   #9
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I know what you are saying but if you use AFR then there is an implied conversion from the output of the device (which is lamda) to an air to fuel mass ratio. Readings in lamda tell you how far from stoich you are regardless of fuel type. Leaving the conversion in the wideband device could be sufficient but why have it convert in the first place if there is no need? Plus if I see numbers in lamda then I know that it's the actual number not something else that may or may not have been recalibrated for a different fuel.
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Old 12-07-2006, 12:47 AM   #10
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So in conlcusion, if I am injecting 50% water 50% methanol to my car on 93 octane through a .9mm nozzle and a 1.0mm nozzle, what target AFR using a gasoline WB sensor should I shoot for? What would be your best guess?
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Old 12-07-2006, 09:02 AM   #11
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I'd try to stay at a reading of 12 to 1 or leaner.

peace
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Old 12-07-2006, 11:30 AM   #12
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Thanks
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