[Diy_efi] WBO2 and AFR

[gary]

I, Gary, do not claim to be an expert (as previously mentioned) as
I am not, nor do I consider my answers infallible.  Likewise, I do
not have a major interest in how my knowledge (or lack thereof),
of this topic is judged by others on this list.  I do however, have
an interest in the accuracy of the info posted on this list.  I also
have no problem recognizing the advanced engineering training
and experience of a Bruce B.  One can be in awe of the accuracy
of the knowledge obtained through the experiments/tests that
were conducted by the likes of a Haywood, Glasman, or a Taylor,
that have also stood the test of time.  In the context of this topic/
discussion, I have no issue with putting Bruce in the company,
of the likes of the above men.

Having stated the above, I still need to state the following.  Regard
less of the minor ?? differences of the various sources of WBO2 info,
in regards to influences (or lack thereof) of gases, or other factors
that affect the ultimate accuracy of the data the sensor sends to the
meter/controller, that although important, need to be put into proper
perspective.  By how much, would these 'influences' affect the
accuracy?

Not attempting to put a figure on it, but if we are concerned about a
couple of tenths (from say 12.5:1 to 12.8:1) we should be tuning on a
chassis dyno.  Personally, I'm more concerned about the consistency
from cylinder to cylinder.  The deviation can easily vary over a full
point (say from 13.0:1 to 14.0:1), depending on combination of the
components of the induction or any given engine design.  People,
this is more common than you may realize.  Therefore, I'm more
concerned, that if one bank (if using 2 sensors @ engine) is reading
12.7:1 collectively, is there one particular cylinder that is 13.7:1. To
do WB sensor testing/tuning with a respectable degree of precision,
it becomes necessary AFAIC, to incorporate a WB sensor in each
cylinder, as per competent pro race teams do.  How many go to
this much trouble/effort?  How many 'so called' tuning shops, don't
understand this?  Apparently, some on this list, be they professional
tuners and/or authors, do not.

GAS


----- Original Message ----- 
From: "Bruce A Bowling" <bbowling at earthlink.net>
To: <diy_efi at diy-efi.org>
Sent: Thursday, July 07, 2005 8:57 AM
Subject: RE: [Diy_efi] WBO2 and AFR

> The point of this is that if you use Lambda to tune then the fuel
> composition is of no consequence. But if the meter is reading in
> AFR units, then it is assuming a fuel composition and you had
> better be running this exact composition, or the meter needs to
> allow you to adjust the conversion by specifying direct H/C or
> O/C values to get the AFR values in whack based on the fuel
> really being burned.....
>
> But here is the wrinkle - this only works for recalibrating the stoich
> point. Move off of stoich the whole wideband curve moves based
> on fuel composition, both lean and rich directions. A lot of this info
> is on the PWC web site - look in particular the Brettschneider
> equation and the fact that the WB sensor is sensitive to not only
> excess oxygen (on the lean side) but also to CO and H2 (and also
> unburnt HC) on the rich side. So to do this right one needs the
> sensor sensitivities to O2, CO, H2, and HC of a particular sensor
> (obtained from flowbench data, verified by gas analyzer) and then
> use the chemical balance equation to determine lambda (in essense
> a reverse Brettschneider). The rich side is the interesting case, in
> that there are multiple solutions (lambda is dependent on CO and
> H2 and HC)  so one has to use tricks like invoking the water-gas
> equilibrium, which now requires the knowledge of the exhaust gas
> temperature at the sensor head (or at least a good guess). Note
> that the LA-3 meter (and the PWC when I finally get time to finish
> it) use this method, you have to specify H/C, O/C and water-gas
> equilibrium temperature, as well as calibration factors. Not mentioned
> is correction for pump current offset, a big effect right near stoich....