Date: Sat, 6 Dec 2003 20:50:08 -0500
Reply-To: Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: Wheres Waldo (EGR or no EGR)
In-Reply-To: <20031206222304.85462.qmail@web11306.mail.yahoo.com>
Content-type: text/plain; charset=us-ascii
A complete EGR system does not affect the fuel mixture. In a normally
running engine, there should almost no unburned fuel or excess oxygen.
In theory, exhaust gas is inert and that is the basis for EGR operation.
During normal operation, some exhaust gas is routed into the cylinders
to basically take up space. This has the effect of reducing the cylinder
charge and on a dynamic basis, lowering the effective compression ratio.
This reduces the peak flame temperatures which reduce the production of
NOx. The additional benefit is that it allows more advanced ignition
timing as it reduces detonation and lowers piston and head temps. The
EGR valve is closed at idle and full throttle. For the emissions point
of view, full throttle operation is a short term event. In addition,
full throttle enrichment also lowers that peak flame temp.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Jake Beaulieu
Sent: Saturday, December 06, 2003 5:23 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Wheres Waldo (EGR or no EGR)
Ahh, the old EGR discussion. When I acquired my 82 Westy the EGR filter
had rusted away so the PO simply plugged the pipe going to the EGR valve
and the hole on the crossover pipe with gobs of JB Weld. I spent a wad
of cash on a new EGR filter and crossover pipe to get this system up and
running again. Since I made this investment I have run into many other
folks who have bypassed their EGR to save cash and claim it makes no
difference. So here is my take on it.
The computer is programmed to expect the exaust gas to be injected into
the intake during heavy acceleration. The exaust gas contains
combustable hydrocarbons that weren't combusted the first time through
the combustion chamber. When this extra "fuel" is not present the
system is actually running lean. Not good.
Additionally, the exaust gas decreases the temperature of the combustion
chamber. This is going to protect your valves and decrease the
production of NOx. In summary, disableing the EGR system will result in
premature engine wear, less than optimal performance, and unquestionably
increased NOx emissions (i.e. ground level ozone and acid rain).
Maybe the valves are constructed to withstand the higher combustion
temperature. Maybe the amount of uncombusted fuel in the exaust stream
is negligable so the engine isn't running lean. I don't know. I spent
the cash rather than take the gamble. Anyone out there have some solid
answers?
Jake
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