O2 sensor?

Blueskies wrote:
Saw this posted to the Lycoming group, and it sounds like a pretty good idea. Anybody heard of it?

"A friend flying an IO-360 powered Glasair installed an oxygen sensor
system that has an panel mounted indicator light to show when balanced
combustion is reached. He simply adjusts mixture until the light comes
on and knows he has complete combustion (his theory is that EGT is
really just a good guess). He has had very good results from this
system in terms of fuel economy and performance.

I believe he purchased the system from Wag a few years ago. As I
recall it was for experimentals only. They do not currently list such
a system in their catalog. I have not found one at ACS&S or Chief either."




Ok.. here's how it was explained to me, including stuff in the past few
days.. I am not speaking authoritatively, only repeating from a collage
of sources i've come across in the past 3 years.

The oxygen sensor is automotive. The indicator is automotive. You will
not find it in aviation catalogs. Go to your local auto parts store or
to a speed shop, or an online auto parts place like Summit Racing. They
sell sensors, indicators, and combination units.

A one wire sensor is a narrow band sensor and has a very narrow
detection range. It has a steep curve that corresponds to a range that
is immediately around stoichiometric air/fuel ratio (which corresponds
with peak EGT). The sensor only senses properly when its heated to at
least 800 degrees, so engine has to be operating for a bit to achieve
this. The bandwidth of the sensor may be inclusive of "best power" which
is slightly rich of peak. It is NOT inclusive of the optimal lean of
peak point, and this indication will be off scale - low.

A 3 wire sensor incorporates a heating element, to allow greater
responsiveness during initial starting and warmup. This is not necessary
for a mixture monitor observed by the pilot, but finds use in emissions
control for closed loop EFI's.

A 5 wire sensor incorporates a nonconsumable oxgyen generator of some
type, in addition to the heating elemet. I do not know how its
generated, but a mixture monitor or EFI that is able to offset the
oxygen reading with the oxygen generation value can be used as a wide
band oxygen sensor and can give a wide range of air fuel mixture
indications. This can reportedly be used to indicate optimum mixture for
lean of peak ops.

An EGT being used in a closed loop EFI situation must respond nearly
instantaneously.. in milliseconds. Being used in leaded fuel will
quickly render the sensor unuseable in this setting, for this cause.
However, even when the sensor degrades to perhaps 1/2 a second lag time,
this is still quicker than you can adjust the mixture manually, so even
in a leaded fuel situation, you can get a lot of life out of an oxygen
sensor.

One of the folks in the Rotary engine crowd has reported getting 85
hours out of an ordinary 1 wire oxy sensor with nothin but 100ll.
Running auto gas can sometimes undo the lead fouling to the point the
sensor remains viable over its normal service life.

1 wire oxy sensors are cheap as far as aviation prices go. Changing it
every 50 hours with your oil filter wouldnt be out of reason.

In my opinion the problem that would emerge here is the fairly common
circumstance of 4 different cylinders operating semi independently.
Until or unless you get them balanced (Gami?) so that they peak and/or
stumble together, an oxygen sensor on one pipe will indicate that one
pipe. If its after a collector it will present an average, and you could
still have a cylinder in the "danger zone". Under 75% power this likely
isnt going to be a problem. You can use it to find ideal mixture, then
manually lean from there.