Ox sender actual function

[Mark Wilcutts]

On Wed, 25 Nov 1998, Greg Hermann wrote:

> > If anything, they were annoyed because
> >they had been told by the manufacturers "this sensor senses oxygen", and
> >they found in their misfire tests that it didn't, as many of us have been
> >told, and are understandably annoyed.
> 
> It does sense O2. The physics of it are "theory", yes. But pretty damn well
> confirmed theory, and over a far longer period of time than the period
> during which the price of making the cells got down low enough to make it
> practical to use them on vehicles. These cells have been used in the
> exhaust stream of large stationary boilers (to tune a/f ratio, and thus
> improve boiler efficiency )  for decades!! They work, and work as claimed.

If by "theory" you mean the Nernst equation, the EPA authors cite a GE
report that states that temperatures of 850 deg. C or more are needed for
a zirconia cell to operate strictly as an O2 sensor. Below that
temperature, the change in voltage due to oxygen alone was reported as
negligible. When reducing species are present, all bets are off as well.
I'll scan in page 6, which talks about the GE findings.

> (For us it means we can't build our
> >own AFR sensor!)
> 
> WANNA BET??? Stay tuned!!

Sorry, I misstated myself, what I should've said is that we can't use the
voltage output of a normal oxygen sensor to back out AFR.  Looking forward
to seeing your design... 

[rant about taxes and greenhouse gases deleted]

> >> <<However, very rich A/F ratios did not result in hIgh port sensor
> >> voltages when there was no ignition.>>
> >>
> >> No surprise here either.  No ignition means 20% oxygen, same as
> >> on the other side of the sensor - so no voltage produced.
> >> The sensor really measures 'lack of oxygen' in the exhaust.
> >
> >Ah, but where the surprise comes in is that at higher misfire rates, the
> >sensor indicates rich!
> 
> So either soot fouls the sensor, then burns off, or the high misfire rate
> cools it down out of its operating range--or both--where's the surprise in
> that????
Pls. see my reply to Orin Eman.

> >> <<These results indIcated that some physical property of the unburned
> >> air/fuel mlxtures, such as the relatively high  concentrations of
> >> hydrocarbons. or the absence of other types of reducing agents,
> >> such as hydrogen and carbon monoxide, inhibited the voltage generating
> >> capabilities of the sensors.  >>
> 
> Like I said above--the physical property in question is pretty likely
> sensor temperature. Did they document the temp of the sensor when it did go
> to a rich indication??

One would have to look at paper 980298 to see details on this.