From: PWeber@swri.edu
Date: Fri, 19 Mar 99 11:34:56 CST
Reply-To: <PWeber@swri.edu>
Subject: RE: SP rules on catalytic converters (Very Long, but informative)
I kept telling myself I wouldn't get involved in this discussion but the level
of misinformation has pushed me over the edge.
>>A well maintained, tuned, and well designed motor, will run very very clean.
Compared to a what. A catalyst equipped car? Not even close. Granted a
well-tuned engine will have lower emissions than a poorly-tuned engine, but
that is a given. What we are talking about is what comes out the tailpipe.
As an example, (pulled from an actual vehicle test run on a chassis dynamometer
over the Federal Test Procedure (FTP) for emissions, NOT a guess or what I
think is true, or what I heard from someone else), a well tuned, 1997 4.6L
engine which meets the California TLEV regulations (Transistional Low Emissions
Vehicle, which isn't very low or difficult to achieve on most modern port fuel
injected vehicles, even trucks) puts out (at idle, warmed up engine) 2,500
ppmC (parts per millon carbon) HC (hydrocarbon), 6,000 ppm CO, and 90 ppm NOx.
HC emissions are mainly a function of crevice volume, CO is the result of
incomplete combustion (from wall quenching), and NOx is a function of engine
load (which is why it is so low at idle). The usual aftermarket engine
modifications are not going to significantly change the engine-out emissions
while operating in closed-loop, period. If the vehicle was not equipped with a
catalyst, this is the level of emissions which would come out and be measured
at the tailpipe.
Measuring the emissions after the catalyst for the same vehicle at idle, same
test, same point in time (exhaust gas temperature = 450°C, catalyst bed
temperature = 600°C) resulted in 6 ppmC HC, 0 ppm CO, and 9 ppm NOx (note
10,000 ppm = 1%). That is a 99.7% percent reduction in HC, a 100% reduction in
CO, and a 90% reduction in NOx for the catalyst equipped vehicle. Anyone who
believes that a well running non-catalyst equipped car can be made to run
almost as clean as a well-runing catalyst equipped vehicle is just plain wrong
and uninformed.
>>My NOX numbers were higher than normal, but within spec. With a cat, I
tested darn near 0 cross the board.
To certify a modern day vehicle you need to have almost 100% catalyst
conversion efficiency at idle and low load conditions. The only time emissions
are high on a modern day vehicle is at cold-start (rich engine operation and
cold catalyst) and WOT (drops out of closed-loop and runs rich to protect the
engine and catalyst components). A side note, severe WOT enrichment is going
away with the adoption of the SFTP regulations/test cycle (100% phase-in by
2002).
>>The Supra Mailing list has a -very- large population of users who
pass EPA sniff tests under all sorts of testing procedures (from state to
state).
EPA tests? There are people who have actually run the EPA FTP emissions test
for smog tests with their personal vehicles? I don't think so, the FTP is a 40
minute test that requires a 12-36 hour vehicle soak prior to starting the
engine. I believe you are speaking about the MUCH less involved idle or IM-240
tests (run on a dyno). The FTP is the test cycle the manufacturer's must run
to certify a vehicle and is much more reprensetative of actual driving than any
of the quick tests.
>>The most common cause of failure is a bad O2 sensor, and plugged up EGR
systems. (assuming the motor is in good shape..etc)
This is true IF your vehicle is equipped with a catalyst.
>>Convertors only work in a relatively narrow temperature rance. They don't
work well cold, and don't work well when too hot. They are for cars that are
NOT maintained well, do NOT run well, or are inherently bad designs and dont
burn as clean as they could.
Wrong, wrong, wrong, wrong. Typical automotive catalysts of this
generation (NOT the pellet catalysts of the '70's) operate quite well
in the 350-1000°C catalyst bed temperature range. If you get your
catalyst over 1000°C you most likely have a misfiring cylinder.
They do not perform well when cold, however newer palladium technology
catalysts have light-off temperatures (defined as 50% conversion
efficiency) at temperatures as low as 250°C ( and this is in an
aged condition). A catalyst does not work well when engine-out
air-fuel ratio deviates significantly from stoichiometry (about
14.5-14.7 for non-oxygenated gasolines). If a car doesn't run well,
putting a catalyst on it will have minimal effect on reducing the
tailpipe emissions.
Please point-out an inherently bad engine design (from the last 15 years).
Every engine I know of built in this timeframe used in a passenger car sold in
the US combusts completely at least 97% of the fuel brought into the cylinder
(again assumes a well-tuned engine operating in closed-loop) at idle to
moderate load conditions.
If you are passing an IM-240 type test with a vehicle that does not have
catalysts, it is probably a pre-91 or pre-86 vehicle (these years were steps in
emission regulations), or the operators do not know how to run/calibrate their
equipment properly.
Phil Weber
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