[RustyLugNut]

When you look at the graph on the first post, you notice the NOx spike just past the 16:1 AFR? That air to fuel ratio is your most economical mixture. It is the mixture that provides the most useful cylinder pressure for the least fuel burned. Why is that? It is because flame speed is still high and there is the additional "fuel" value of some of the nitrogen oxidizing! More power through pollution!

If nitrogen was not such a "lazy" reactant and required temperatures approaching 2300 deg C to oxidize, we would be able to use it as a fuel!

On the other hand, some of the builders of the first nuclear bomb had a fear that the fission explosion would set the atmosphere on fire. The nitrogen all oxidizing into NOx due to the temperature extremes caused by the nuclear fire. The physicists knew better and were not bothered, but lesser minds ran with the idea.