Quote:
Originally Posted by Skippy
Edit: I just remembered a bit about ignition timing. Later timing can decrease NOx at the expense of higher HC and CO. Have you checked the timing on the thing?
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Half-right half-wrong! Retarding spark advance reduces peak combustion temperature, which reduces engine-out NOx.
It also INCREASES EGT, which will keep the catalyst hotter making it more effective at oxidizing HC and CO.
Shorting the R16/1 resistor along with plugging the vacuum advance signal line yields signficantly retarded spark advance under loaded dyno emission test conditions.
The reduced rate of spark advance with revs with no contribution from the vacuum advance at moderate load creats a dramatic reduction in engine-out NOx, and the hotter catalyst promotes maximum oxidation of HC and CO.
If the O2 content is zero, the catalyst is hot enough to be working at peak effciency by using all the O2 exiting the cylinders and formed by the disassociation of NOx.
If O2 is more than 0.2 percent the catalyst is either degraded or not hot enough to maximize all potential reactions.
Duke