Bill:
Wonderful. This is an area that was way too gray for me.
Thanks.
kelvin.
-----Original Message-----
From: REwald9535@aol.com [mailto:REwald9535@aol.com]
Sent: Saturday, November 28, 1998 7:19 PM
To: doddk@mossmotors.com; saidel@crab.rutgers.edu
Cc: mgs@autox.team.net
Subject: Re: some car mechanic help
Bill,
Kelvin got it mostly right but his description of EGR valve and what it
does
was not right.
EGR is a method of controlling oxides of Nitrogen. (NO, NO2,NO3 , etc.,
usually referred as NOX.)
First a little chemistry. When air goes through an engine about 79% of
what
is sucked through the intake is Nitrogen. If the temp in the cylinder
stays
below 2500 degrees F the Nitrogen goes out the same way it went into the
engine as N2. However if the temp in the cylinder goes above 2500
degrees F
then the two Nitrogen split apart and start grabbing oxygen atoms 1, 2,
3, 10
what ever they can find. These NOX molecules are not stable, and are
very
reactive.
These strange oxides of Nitrogen then go into the air and become part of
smog.
Oxides of Nitrogen are what cause the burning in the lungs and eyes on
smoggy
days. (the oxides combine with water and create Nitric acid, no wonder
your
eyes burn!). Needles to say this stuff is bad for you.
Now in the days when the air was clean and sex was dirty (early 60's),
nobody
talked about NOX because the mixtures were so rich the temp in the
cylinders
was always 2500 degrees F. Then 68 rolled around and the Feds. made the
auto
makers make their mixtures leaner. All of a sudden there was NOX coming
out
of the tailpipes of cars.
The automakers were faced with having to get rid of NOX, in the early
70's
there were three ways to do this:
1. Lower compression Less pressure, less temp (really bad for
performance)
2. Retard timing same effect as #1 (also not good
for
performance)
3. Put two to three percent by volume when needed into the cylinder to
lower
the peak temp. This is what EGR does. It allows the car maker to keep
some
performance in what would otherwise be a smog strangled engine.
(yeah!)
When does EGR work?
When the potential for high cylinder temps and pressures exists. During
idle
the pressure in the cylinder is very low, and EGR is not needed. In
fact EGR
at idle will cause a rough or possibly no idle condition.
During full throttle there is so much fuel going into the cylinder that
the
temp does not go above 2500 degrees F. EGR is designed to work at part
throttle cruise.
Sorry I went on for so long,
I hope this helps
Rick Ewald
67 B roadster
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