EGR Systems

[Mayhem_J30]

I love picking the techs brains...As with the PCV thread I'm determined to systematically learn about the motor systems.

Now as I understand the EGR system is supposed to divert exhaust back into the intake manifold when a stoich air/fuel mixture is obtained. Lets get to fact vs myth killing here. Is the EGR for environmentalists only or does it actually cool the combustion chamber? or does it actually do both? I can understand the enironment issue by reburning spent fuel, but the cooling process boggles me. Recirculating hot exhaust fumes back into the cylinders doesn't sound like a cooling method to me. It also seems that the exhaust would consequent in a loss of power as the oxygen is already burnt. If that's the case the air/fuel mixture would no longer be stoich...correct? In which case the EGR should close, right?

Back to the environment questions. The EGR on the VG only pulls exhaust (from what I can see) from a single exhaust manifold. Why not use both? Only using one leads me to believe the EGR system IS actually for cooling and not for environment issues. Otherwise both would have been used to effectively reduce emissions.

[Sopdadope]

Emissions-wise, EGR's sometimes backfire. Just look at GM's EGR's..

[Q45tech]

Think of exhaust gas as cool because it contains little oxygen but still takes up space in the incoming charge.

Tests have shown that 10% EGR plus 90% air reduces oxides of Nitrogen produced by 75% at cruise you don't need to be generarting much power just enough to keep the car at speed and AC turning.

The burning temperature of the flame is reduced because there is 10% x 23% or 2.3% less oxygen in the same volume of air in the cylinder at cruise this drops things by 300F.

Sure the EGR is probably warmer than the incoming charge but 10% probably only heats the plenum air by maybe 40F at cruise.......since EGR is cutoff on acceleration at most the power might be down for the first quater to half a second until the 10 times more volume gets to the plenum............this all takes place while the transmission is downshifting as the EGR is cut off when the throttle is pushed down by vacuum changes which occur long before your foot reaches the floor!