EGOR - how is he under PRESSURE?

garfield at pilgrimhouse.com garfield at pilgrimhouse.com
Wed Jun 3 05:30:41 GMT 1998


... actually, for that matter, the issue doesn't just concern EGOR, but
ANY/ALL them O2 meter boxes sold for them big huge bucks! Perhaps the
subject should read "NTK UEGO - how is it under PRESSURE?".

This all got started when Brock Fraser sent me a question/comment about
a report he'd read on these sensors being exhaust system pressure
sensitive, and what one engine mgmt. system had done to
compensate/calibrate for this dependency. He said he couldn't recall
this ever being discussed (actually it did come up very briefly during a
technoblurb on the basic technology, from one of our electrochemical
types on the list), and so what ensued after that was I went back and
dug out the NTK/SAE paper to see why I had dismissed this as a
non-issue, as well as why I presumed all the vendors of O2 meters using
the NTK sensors had also.

I'll try to summarize the traffic that has passed between Brock and I,
regarding EGOR and NTK stuff, and then if Brock wants to fill in any of
the Deere info he feels at liberty to discuss, you'll have as full a
picture as possible, and be as up-to-speed as anyone.

I looked up the quote in the paper on this, and sent him back the
following message and quote:

**** message extract begins ****

The SAE paper by NTK makes
mention of the pressure issues, lemme dig it out and remind myself of
why I didn't worry about it; dadadum dadadum, let's see, it says ... OK,
they're discussing the issue of both temperature and pressure
dependency, having just derived all them equations for both, and say:

[comments in brackets are mine-Gar]

"Although practical dependence is at the level shown in Fig. 10 & 11,
[figure 10 shows a 2% error per volt delta on the heater element, and a
3.6% error from a delta of 1.5psi in exhaust gas pressure] the diffusion
opening was made to be porous showing relatively small temperature
dependence and a little larger pressure dependence. It was decided by
considering that, when it is installed to a practical engine exhaust
pipe, the sensor output change due to exhaust pressure change can be
easily corrected by other information, for example, engine revolution
and intake manifold pressure, while the sensor element temperature
cannot be easily compensated. Furthermore, the parameters affecting
sensor output in the engine exhaust are not only temperature and
pressure, but also the dynamic pulsation and nonequilibrium of exhaust
gas. Therefore, we finally decided [on] the porous diffusion type which
showed less sensor output error for all engine operating conditions."
SAE #920234

[You gotta get that one; it's very well written and explains bloody
EVERYTHING, including some simplified EGOR entrails. Heh.]

I remember thinking, well on racing cars and airplane exhaust systems,
there'd better not be much more than a few tenths of an atmosphere of
back pressure at WOT, and it better not be varying even a tenth of that
much around that point, especially in regimes where the leaness/richness
of the mix is critical, otherwise we're in big trouble.

**** message extract ends ****

His (Brocks's) response might be summarized as "yes, that's OK, but what
about those meter vendors whose meters are being used to measure exhaust
gas O2 in stock auto's with dual cats and potentially more restrictive
exhaust systems".

Brock's own work is in whopping big diesel engines that probably don't
represent too well the kinds of levels and variation of pressure levels
found in ordinary automobiles, so neither of us really knows at this
point just how much of an issue this is. That's another reason for
needing to get this out to the group for discussion, cuz there likely
will be some who HAVE instrumented and can give us an idea on what kinda
exhaust backpressures can be expected in both stock and performance
engines/exhaust systems. Especially anyone real familiar with the design
of EGR systems would probably know, since I know at least SOME of those
systems were very sensitive to exhaust gas pressure levels.

Anyway, that's all we know about this at the moment. I imagine this will
create another Energizer Bunny Thread, but it's gotta be opened up for
discussion, so we can either worry or put the sucker to bed. But
whatever it means for EGOR, it ALSO means the same for the Horiba, NTK,
and ECM boxes, as well. Curious, no?

Gar




More information about the Diy_efi mailing list