eec egr scheme

[EGR NATIC]

>It seems to me that if you throw in more inert exhaust gas, and then
>don't compensate by putting in less fuel, the mix will be rich. If you
>ran the engine on pure oxygen (no nitrogen) and did not compensate by
>adding more fuel, the mix would be lean. What am I missing?
>

The air / fuel mixture is determined by the flow thru the MAF.  The EGR 
is ingested down stream.  The MAF doesn't see the EGR gasses so the 
mixture remains correct.  On all systems, the EGO (Closed Loop) corrects 
the mixture such that even if it did go "rich" it would only be loop 
settling time to correct it out.  

The EGR gasses are N2, CO2 and H2O with a smattering of other products 
(NOX, unburned HC, CO etc).  The primary effect of adding EGR is that 
these gases act as heat absorbers during compression and combustion - 
lowering the temperatures - thus lowering NOX and incidently, increasing 
the effective octane of the fuel.  They also, by absorbing heat, slow 
the combustion flame rate.

The addition of these inert gases effectively slows the burning rate as 
if a leaner mixture was used, while allowing the EGO to maintain the 
chemically correct mixture to make the cats happy.  It also allows the 
PART THROTTLE effective compression ratio to be significantly higher and 
thus increase the economy of the engine under light to moderate loads.  
Properly done, for all but an all out racing engine, EGR can make 
substantial improvements to the drivablity and economy of an engine.

Habeneros - not just for breakfast anymore!!
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