egr
I think that the egr valve ( exhaust recirculating gass) valve is used to lower NOX. It is used in this manner by mixing the exhaust gass with the air,when the fuel is injected to burn not as much as heat is generated. Slower timing also reduce NOX. In gasoline engines the low compression engines have a built in egr in a way because the left over gasses from the last cycle delute the fresh charge depending on how much scavaging of the exhaust and valve overlap. I think that the cumbustion chamber design along with the shape of the piston also effect the temperture of the gasses as to be what is called quench and squelch. As to push the gasses to a small areas and not expose the compressed gasses to the a large surface to absorbes the heat and cause preignition in a gass engine. I read where rod ratio, also has some effect on this also, because a longer rod will park the piston a little longer at the top of the cylinder, thus making more torque, and picking up a little more heat and has a tenency to preignite. In power generation, we reduce the air to help reduce NOX along with boiler tuning. I hope that I have not strayed to far off of the subject. lol Jim I wish that I had spell check on this form