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
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