Mike Wills wrote:
At 09:17 AM 5/12/99 -0700, you wrote:
They could be fooling themselves as a lot of fuel injection systems that
see the O2 sensors fail, default to an open loop system and don't use
the sensors. Sometimes the only indication is a slight increase
in fuel consumption. Another possibilty, and this is the case with
my Ford EFI, is the EFI CPU only uses the sensors at medium and low
power. At aircraft power levels it does not use the O2 sensors
at all.
Unless you have the source code for the software in the engine computer
or a software flow chart it is difficult to tell what is really
going on.
It is a fact that leaded gasoline destroys O2 sensors eventually.
Since Tracy programmed his own computer and has some eperience
with O2 sensors and has burned both 100LL and no lead auto fuel
he tells us, as I recall, that the sensor will recover somewhat
if no lead auto fuel is burned after 100LL is burned.
Tracy?
Paul Lamar
Mike Wills wrote:
One of these guys was using a carburetor, the other an Airflow performance
mechanical fuel injection system. The O2 sensor is used just as Tracy uses
it, to drive a gauge to monitor mixture, not as an active component in an
EFI system. They both installed this as a supplement to EGT to aid in
leaning. Both claimed that they took detailed data on mixture, MP, and EGT
when the O2 sensors were installed to be able to determine when/if the
sensors failed. Both claim that the sensors still perform now exactly as
they did when installed. My only point is that based on their history and
considering the relatively low cost of replacement, I wouldnt be overly
concerned about burning 100LL as long as continued engine operation was not
dependant on the life of the O2 sensor.
Mike Wills
Maybe the EPA/CARB are lying about putting leaded gasoline in
our cars. :-) They say the lead kills the O2 sensors (and the cat).
Bosch says the same thing. We have a petroleum engineer on here that
has
some first hand experience with the subject.
Bob Falkiner are you there?
Here is one of Bob's old messages on the subject.
Paul Lamar
Quote:
You may be asking the wrong questions around lead tolerant O2 sensors.
What happens to the signal is that the range gets decreased. If you
have
an engine control strategy of counting the rich/lean cyle crossings,
then not
much of an issue, as it is simply a gain/amplifier type effect. If
however you are trying to get an analogue signial out of the sensor as
a continuous linear function of oxygen then you have a problem of sensor
output vs o2 level in the presence of anything (like lead) that changes
this over the lifetime of the sensor.
Bottom line is that you have to be careful how you ask the question
around
lead tolerance of oxygen sensors. There is obviously a lot of political
science around this one!
End of quote one.
Here is another one.
Quote:
Ethyl Corp and DuPont did a lot of research in the 70's on lead tolerant
catalysts, effects on oxygen sensors, lead traps etc looking for
alternatives to total unleaded gasoline. Much of this work is in the
SAE
liturature, and all of this work predates the now standard 3-way
catalyst
technology which uses the rich/lean "digital noise" type strategies that
were more or less universally adopted by the OEM's. This fit the classic
voltage/concentration curve shape that is defined by the basic Nernst
equation for electrodes (which is what an oxygen sensor is) . Most
people
are familiar with pH acid/base shaped curves where in a titration (like
going from lean to rich) you have a very slow change in voltage in the
initial stages, a very rapid change near equivalence, and a gradual
change
after equivalence.... a classic "S" shaped curve between two almost
horizontal lines.
Electronically if you amplify this, you get a square wave, and get rid
of
calibration problems. This in a nutshell has been the basic strategy of
engine control up until now with the advent of lean burn engines that
need
a more analogue control on the lean side.
bottom line... if you take an existing heated O2 sensor, it is probably
a
lot more tolerant of lead than the brochures imply if the amplitude is
sufficiently amplified to create a square wave rich/lean output. You
are
doing research at this point, but it would be fairly easy to veryify in
an
aircraft, since you have an absolute control of air/fuel ratio at any
time
with the mixture control.
On levels, i (going from memory) think that avgas 100LL has about 500
mg/l
max lead (Pb) vs 13 mg/l in USA unleaded gasoline. The industry average
is
probably in the 300 mg/L range, as Avgas100ll formulation is designed to
reduce Pb from previous 1000+ levels. This is well below even the old
leaded car gas levels, and there is still a lot of activity trying to
get
it lower without compromising octane Performance Number (Supercharged
rich
rating).
hope this helps.
End of quote.
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