Quote:
Originally Posted by mwebb
somehow this subject keeps being reposted
somebody gets it in their mind that removing the EGR system helps the engine run better and somehow magically increases power output and improves fuel economy
all of that is pure blarney -
EGR does not function at idle or WOT - and does not affect maximum power output .
EGR does function at part load or cruise .
the Primary function of EGR is to add INert exhaust gases to combustion to reduce combustion temperature and by so doing
reduce the formation of the pollutant NOX
EGR improves fuel economy by reducing suction throttling loss and reducing engine compression and reducing engine displacement
BY DILUTING THE AIR FUEL MIXTURE IN THE COMBUSTION CHAMBER WITH INERT EXHAUST GASES
while it is active
deleting EGR is going to cause your system to pollute more and it will reduce FE , deleting EGR will have no affect on maximum power available.
and on a 1996 or newer car ;
doing anything to interfere with EGR function is "tampering " with the OBD2 system and a violation of federal law .
bottom line ;
if you do not know EGR theory ....
do not frak with your EGR unless you need to clean out the passages to IMPROVE / INCREASE EGR flow .
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Basically correct.
I respectfully disagree with the reduction of suction throttling losses and reduction of compression and displacement statement.
Does it reduce suction throttling losses?
Yes.
Does it reduce compression?
Actually it would increase compression by allowing more mixture into the cylinder to be compressed, but that is offset somewhat by the dilution of that mixture with a basically inert exhaust gas component.
Does it reduce displacement?
Not in the sense of mechanically reducing the physical components of compression, but in the fact that the intake charge would be at a higher temperature than it would be without EGR, and therefore less dense, then the effective compression is reduced slightly. On the other hand the volume of EGR admitted with the combustible air-fuel mixture increases the effective compression.
The reduction in peak combustion temperatures by about 300 degrees, dramatically reduces NOX, and allows significantly greater timing advance than what would be possible without EGR.
Recent experimentation points towards strategically using EGR to even greater extent, with some attempts to combine EGR with direct injection and very lean mixtures, to the point where engine throttling can be accomplished without restricting the incoming air and creating manifold vacuum.
Bottom line is if it makes no difference on your engine if it is working or not, it probably is not working properly. We used to check it by pushing the diaphragm from the bottom manually, and it would immediately make the engine stall at idle. Generally speaking EGR is applied at partial throttle positions, and the control of EGR supply has been evolving for 40 years to improve performance and economy. Some modern engines with the greater computation power accomplish EGR through cam timing, specifically the exhaust cam to leave more exhaust gas in the cylinder after combustion, which eliminates all the rest of the EGR system components altogether.
regards
Mech