Dave Kautz writes:

 Back to Nitrogen oxides - I think that the combustion temperature is affected
 by many things. For example, my '72 controlled NOX emissions by turning off 
 the vacuum advance when the engine was warm. I read that richening up the 
 mixture a little will cool the combustion temp somewhat. What I'm getting
 at is that all these things are related:  you may not want to 
 dis-connect your EGR because your injection control unit is setting the
 mixture assuming that some of the molecules in the mixture don't have an
 oxygen to contribue to combustion. The spark may be timed with the same
 assumption. 

Combustion temperature is affected by mixture- the Bentley Bosch Fuel
Injection book has a lovely curve showing CO, NOx and unburned hydrocarbons
as a function of fuel/air mixture. A lean mixture runs hot, making NOx,
but combusts completely and has little CO and few unburned hydrocarbons.
A richer mixture runs cooler, makes less NOx, but has unburned hydrocarbons
and, of course, CO. A three-way catalyst will react unburned fuel and
CO to achieve complete combustion, provided oxygen is available, while
keeping cylinder combustion temperatures down, to control NOx.
	Air cooled engines need a richer mixture than water cooled, but
any emissions controlled motor will be run slightly rich anyway, to control
NOx.	
	BTW, I don't know what the 3 ways of a 3 way catalyst are, I just
know thats what they're called. They don't do diddly for NOx.

	Bill