Factors affecting NO x formation from nitrogen-containing fuels

Abstract

Data from a turbulent diffusion flame burner indicate that the summation of fixed-nitrogen species (NO + HCN + NH i ) is a significant measure of a flame's emission potential. Raising the flame temperature by preheating of the inlet air causes a reduction in the summation of fixed-nitrogen species in rich flames. This reduction occurs over only a narrow range of equivalence ratios and only for flame conditions with low concentrations of unburned hydrocarbons at burner exhaust. Therefore, the fuel and air must be intensely mixed at the entrance of the burner. Flames resulting in soot formation heavy enough to turn the flame bright yellow yield high concentrations of unburned hydrocarbons and HCN. For rich flames this results in a high summation of fixed-nitrogen species, because HCN is the dominant nitrogen containing species of these flames. The distribution of fixed-nitrogen species leaving the burner is independent of the form of the nitrogen in the fuel; the reduction of fixed-nitrogen species with increased air preheat occurs at fuel nitrogen concentrations as high as 5%.