[alfa] Re: Emissions and sensors

[alfa@xxxxxxxxx]

To kind of accentuate both Simon's and Dave's post about emissions....

Both of you get most of the answer, Dave almost gets the whole story about the
cycling.  The cycling is actually very intentional, besides the fact that the
sensor is so non-linear around stoich.

About 20-25 years ago, a young engineer that a lot of you actually know (not
me), noticed that when the a/f was cycled around stoch, the emissions went down
by a rather large amount.  The best theory I've heard is that the active sites
on a catalyst will hold onto a particular chemical, holding until its reactive
opposite comes alone (NOx/ O2 will wait for CO/ HC  or backwards depending on
the data you look at).  So the cycling continually fills and drains the
catalyst of emissions.  This really happens, just not 100% sure what the actual
chemistry is- up until I was working on the PZEV Focus, I was sure, but recent
data kind of questions the info...

Anyway, the amount of cycling actually will vary depending on the speed and load
of the engine, and whether you can feel it or not.  The computer adjusts the
cycling based on what the calibrator (me) finds as the most efficent and robust
settings are.

Ok, now the short answer- new catalysts should work fine, and the O2 sensor must
cycle to work properly as a system...

Eric Storhok
Ann Arbor, MI
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