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Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Fri Nov 03, 2017 3:49 pm
by Tuner
Easy reading from Klaus. This an excerpt from http://www.innovatemotorsports.com/resources/news3.php where the entire dissertation may be read. Some posting in this thread need to read the entire essay, so click the link Joe, and scroll down.
Klaus wrote:
WBO2 sensors combine a regular NBO2 sensor and what's called a pump cell in one package. The pump cell is kind of the opposite of a NBO2 sensor. It can pump oxygen ions in or out of the sensor cavity. An electrical current through the pump cell transports the oxygen ions. If the current flows in one direction, oxygen ions are transported from the outside air into the sensor, in the other direction oxygen ions are transported out of the sensor to the outside air. The magnitude of the current determines how many oxygen ions/second are transported, just like the electrical current through a fuel pump determines the fuel transport rate.

Both, the NBO2 part and the pump cell, are mounted in a very small measurement chamber open with an orifice to the exhaust gas. The pumping rate of the pump cell is very temperature dependent. Therefore the sensor head temperature must be tightly regulated through a built in heater. A WBO2 controller (like the LM-1) monitors and regulates the heater to keep it at a constant temperature. In a rich condition the WBO2 controller regulates the pump cell current such that just enough oxygen ions are pumped into the chamber to consume all oxidizable combustion products. This basically produces a stochiometric condition in the measurement chamber. In that condition the NBO2 sensor part produces 0.45V. In a lean condition the controller reverses the pump current so that all oxygen ions are pumped out of the measurement chamber and a stochiometric condition again exists there. The pump cell is strong enough to pump all oxygen out of the measurement chamber even if it was filled with free air.

The task of the WB controller is then to regulate the pump current such that there is never any oxygen nor oxidizable combustion products in the measurement chamber. The required pump current is then a measure for the Air/Fuel ratio.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Fri Nov 03, 2017 5:02 pm
by In-Tech
Hi Tuner,
I think we are on the same page as to how the wbo2 and nbo2 works. Thanks for that link though, it was a good refresher.

I passed on what I have seen and my method could be flawed, I also want to state that I am not talking large swings in AFR from the change in timing, just enough that the computer is making adjustments. I would like to explain in further detail some of my methods for excellent idle control (Not too much though ;) ) but I am in the hospital again and just had another surgery last night so my mind is a little slow. I would love to do some further testing later and if another method is learned or I learn what was flawing my method, all the better. Carry on :)

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Nov 07, 2017 11:01 am
by Tuner
Warp Speed, knowing you are busy on week ends nobody expected you to comment on this thread in the last few days, but can you offer some insight into why the WBO2 indicated A/F changes when ignition timing is changed? Also, as others mentioned above in this thread, the A/F numbers generated by the dyno air and fuel flow sensors change too. Curious indeed. Can you share your experience and your dyno generated information about this?

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Nov 07, 2017 11:48 am
by nickpohlaandp
Tuner wrote:
Tue Nov 07, 2017 11:01 am
Warp Speed, knowing you are busy on week ends nobody expected you to comment on this thread in the last few days, but can you offer some insight into why the WBO2 indicated A/F changes when ignition timing is changed? Also, as others mentioned above in this thread, the A/F numbers generated by the dyno air and fuel flow sensors change too. Curious indeed. Can you share your experience and your dyno generated information about this?
I'm not saying this as scientific fact as if I know for 100% sure and anyone who says otherwise is wrong, but my assumption would be that the AFR would change with timing depending on a few factors, such as whether you are advancing or retarding the timing, and the cam profile being used. Think of it. If you light the charge later in the combustion cycle, there is less time for a full burn. As I'm typing this I'm realizing that I've begun to confuse myself, but I'm sure I'm on to something here. If you light it off later and there is less time for a full burn, then theoretically there would be "air" left over in the charge as it evacuates into the exhaust, showing a leaner mixture, and I would assume the opposite would be the case if you had the timing advanced and lit it off sooner.

Now, someone with a more properly functioning brain, come in here and give us a good explanation, lol! :?

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Nov 07, 2017 12:22 pm
by John Wallace
More like the AFR stays the same, but the combustion efficiency changes.
The O2 is reading unburnt oxygen, which shows inefficient ignition/combustion?
(same ratio of air to fuel, just not all fuel burnt)


:?:

Use a 5 band sniffer at the tailpipe and see if it agrees with the O2?
(or whatever the sniffer things are called)
:)

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Nov 07, 2017 12:43 pm
by nickpohlaandp
John Wallace wrote:
Tue Nov 07, 2017 12:22 pm

Use a 5 band sniffer at the tailpipe and see if it agrees with the O2?
(or whatever the sniffer things are called)
:)
Buttplugs?



Sorry, couldn't help myself

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Tue Nov 07, 2017 2:20 pm
by Tuner
John Wallace wrote:
Tue Nov 07, 2017 12:22 pm
More like the AFR stays the same, but the combustion efficiency changes.
The O2 is reading unburnt oxygen, which shows inefficient ignition/combustion?
(same ratio of air to fuel, just not all fuel burnt)
That does offer a reasonable explanation, but many other factors are in play.

For instance: Changing the timing changes the combustion chamber temperature, valves, piston crown, chamber walls, etc, and that heat affects volumetric efficiency. A hotter chamber will not induce as much mass per volume and vise versa. Given that the air velocity through the carb remains the same (relative to piston speed) for a given RPM, the A/F will remain the same although the air mass density is decreased by a hotter chamber, ergo the A/F would be richer. A conundrum exists in this seems not always to be the case, RCJ reports seeing the opposite.
RCJ wrote:
Thu Nov 02, 2017 12:45 pm
Advancing the timing will show leaner on a flow meter also.
An important variable is how much timing change is causing what influence, if the changes are large or small and how close to ideal timing and on which side of ideal, too much or too little.
:?:

Use a 5 band sniffer at the tailpipe and see if it agrees with the O2?
(or whatever the sniffer things are called)
:)
Yep. On the bucket list.

I'm not bashing WBO2s, in fact the opposite. I agree with Warp Speed, they are reliable and accurate, the most useful tool we have available for engine tuning, carb or EFI, as long as the users understand their idiosyncrasies and act accordingly.

It can only be a good thing to gain better understanding of the circumstances that cause a perception of inaccuracy. The tool is only telling us what it sees, we need to better understand why it sees what it sees. An obvious example is how a too-rich misfire causes lean readings. Other things, like this changing timing changes reported A/F, need deeper understanding.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 08, 2017 10:07 pm
by JodyB
Tuner wrote:
Thu Nov 02, 2017 5:14 pm
In-Tech wrote:
Thu Nov 02, 2017 3:41 pm
Another example is detonation occurring in a rich A/F, where there should be little or no free O2 to combine with N to make NOx, makes substantial NOx and causes WBO2 readings leaner than actual A/F, sometimes much leaner if the detonation is severe.
This!!! :) Seen this many times in heavily turbocharged engines around 11.5 afr. Engine datalogs show slight knock sensor activity, and wideband shows sawtooth pattern in afr corresponding to point of detonation on dyno pull. Great stuff!!!!!!! :)

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 08, 2017 10:16 pm
by JodyB
As a side note; with the dyno sample smoothing turned off, the engine experienced the same sawtooth "noise" in output, correlating to the datalogged knock sensor activity, and wideband afr noise:) Interesting stuff !!

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 08, 2017 10:30 pm
by JodyB
Yes. Wideband 02 sensors will lie to you, if you don't know what to expect. Always best to look at the in-cylinder combustion datalogs. (spark plugs)

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 08, 2017 11:23 pm
by andyf
I think it is like the story about the blind men describing an elephant. One described the trunk, one the tail, one a leg, one a tusk, etc.

Same thing with the wideband, the plugs, the 5 gas, etc. These sensors just know what they know and they do have any context or overview. The tuner has to piece the threads together. Just like my exchange with John on the wideband reading lean when a spark plug wire comes off. An EFI computer will add fuel in that situation since it doesn't know how to look for a missing plug wire. A human tuner should look for the missing wire before adding fuel. Sometimes that doesn't happen of course.........

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Wed Nov 08, 2017 11:45 pm
by JodyB
Agreed. Lots of raw numbers and trends/correlations looking for a good interpreter.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 09, 2017 11:26 am
by David Redszus
So just what happens to combustion when we change ignition advance timing?

If we advance ignition timing a few degrees, the flame speed is increased, the combustion pressure curve is shifted towards TDC, the chamber temperature goes up, the exhaust temperature goes down.

Retarding the ignition timing results in the combustion pressure curve shifting away from TDC, the flame speed is decreased, the chamber temperature goes down, the exhaust temperature goes up.

Changes in flame temperature will change the peak pressure location. Higher combustion temperatures will increase the NOx formation allowing less oxygen available for the oxidation of hydrocarbons and CO.

If we sample lambda fast enough we can see cycle to cycle variances, even with a steady ignition timing angle.
In-cylinder pressure also varies from cycle to cycle. While EGT response is much to slow to indicate temperature cyclic variances, we can derive temperatures from pressure values.

The point is that we have unstable combustion process that is trying to return to some middle value. Mixture changes in response to changing lambda values simply compound the measurement task. What we are always reading are some sort of averages produced by a range of parameter variables. When the range of variances is large enough we can measure their effects and sometimes even observe their effects on performance.

Re: Consistency between Air-Fuel #s on dyno & in-car wideband O2?

Posted: Thu Nov 09, 2017 7:25 pm
by BradH
Hello, it's the OP again. Glad the discussion continues, but I gotta admit you folks are now waaaay past my understanding where it's gone.

Not a complaint, just an admission / observation.