a/f ratio with LPG

[SRavet at bangate.compaq.com]

Darrell Norquay <dnorquay at awinc.com> Wrote:
| what happens.  By the way, O2 sensors do read oxygen content, at least in
| that they are proportional to the difference between the exhaust O2
| concentration and the ambient air.  They are unaffected by concentrations 
of
| other gases, and generate a voltage by pumping O2 across an 
electrochemical
| cell.

This is a post that Dale Ulan sent in about a year and a half ago about O2 
sensors, in which the EPA published a paper that said O2 sensors don't 
actually measure oxygen until they reach 900 degrees.  Dale didn't have the 
SAE paper number at the time.  If anyone else recognizes this reference, 
could you please post the article number?  I'd like to add this one to the 
EFI reference.  Are you still here, Dale?

------------ begin
That's what everybody thought, too...
About 3 or 4 years ago, a few people from the EPA wrote an SAE
paper on the subject of oxygen sensors. My copy of the paper
is at school, so I can't quote the names or give you the SAE
paper number. But I can summarize it, because I was suprised, too.

The EPA was going to do a study of oxygen sensor aging and break-in
periods, and quantify how this affects exhaust emissions. They
built a test setup with a heater (which would heat up the sensor and
the gas it was exposed to), and a valving system that would allow them
to purge the test system with nitrogen gas, and then give samples
of other gasses.

What they found surprised them... The most obvious test is to see what
temperature was required for the sensor to sense oxygen. So they
cranked up the O2 flow, and started heating. The O2 sensor started to
respond at about 800 or 900 degrees C. No exhaust system operates that
under normal road-load conditions.

At this point, they decided that their study should concentrate on this
lack of O2 sensor activity. What they discovered was that the O2 sensor
would respond to carbon monoxide and hydrogen. At normal operating
temperatures, they concluded that the O2 sensor is not capable of
sensing oxygen at all. Few people seem to have read this paper, though,
so most people out there think that the oxygen sensor actually senses
oxygen in a vehicle. It *can* sense oxygen, but it'll have to be
glowing pretty bright to do it.

I would suggest going to your local technical library and finding
this SAE article. It will be in one of the annual article abstract
books, somewhere between 1989 and 1993, and may be present in either
the big thick SAE publication hardcovers, and/or in 'Sensors and
Actuators', an SAE special publication series.

I haven't seen any papers arguing against their conclusions,
but if there are, I'll hopefully eventually find them and read them.


-Dale

----------- end


Steve Ravet
sravet at bangate.compaq.com
Baby you're a genius when it comes to cooking up some chili sauce...