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Oxygen sensors
> From quattro-owner@swiss.ans.net Fri Feb 24 13:19:36 1995
> Date: Fri, 24 Feb 1995 09:36:45 -0700
> To: quattro@swiss.ans.net
> From: bbell@csn.net (Bruce Bell)
>
> >Andrew, O2 (Oxygen) sensor senses the amount of oxygen in your exhaust
> >gases....
>
> 10 or so years ago I had a conversation with a Shell engineer about O2
> sensors. He claimed "O2" is a misnomer because they do not actually measure
> oxygen directly. Claim is some other by products of combustion are measured,
> cant remember which he said, perhaps hydrocarbons. Any one else know of
> this? I don't want to create confusion, but I am curious.
>
No, the oxygen sensor uses a special ceramic material which generates
a voltage up to one volt when oxygen is present. Contrary to what many
believe, the amount of O2 in the exhaust increases as the mixture
gets richer (lambda less than one), not as it gets leaner (lambda greater
than one). Lambda represents the excess-air ratio and is equal to
one when the mixture is stoichiometric.
The voltage output of the sensor is therefore low for lambda greater
then one (lean), and then increases rapidly when lambda decreases
from 1 to .995 or so, and then stays close to one volt for successively
richer mixtures.
Maybe the engineer meant that pollution is not measured directly. It
is true that pollution is lowest right where the O2 sensor voltage knee
is, at least when the exhaust is piped through a 3-way cat.
Older cars used exhaust reactors and a richer mixture to reduce
pollutants, but this method traded higher CO and HC in order to
lower NOx emissions. Also, specific fuel consumption was higher
than when tuned for the 3-way cat. I guess that's why pollution
controls got such a bad rap at first.
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John Greenstreet, Senior Engineer (jgreenst@motown.ge.com)
Martin Marietta Government Electronic Systems Moorestown NJ 08057
WPI Class of '75, Temple Class of '94
My new car history:
1975 1978 1982 1986 1989 1992 1995
VW -> Audi -> Audi -> Mercedes -> Mercedes -> Audi -> Mercedes
Scirocco Fox GTI 4000S 190E 2.3 190E 2.6 100CS S320
POSSLQ's* new car history:
1978 1981 1985 1988 1990 1993
Triumph -> Toyota -> Toyota -> VW -> Audi -> Audi
Spitfire Tercel Corolla Jetta GL 80 90S
*POSSLQ = Person of Opposite Sex Sharing Living Quarters
Note: All Audis and Mercedes above were sold to friends or family.
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