Reduced mechanisms for NOx emissions from hydrocarbon diffusion flames

Reduced mechanisms are used to study the importance of various NOx production and consumption mechanisms in non-premised hydrocarbon-air flames. It is found that the prompt, thermal, and nitrous oxide mechanisms for NO production can each be important under conditions realistic for practical combustion devices. Further, the reburn process contributes significantly to NO consumption under certain conditions. In general, the prompt mechanism is the dominant production mechanism when the residence time is shortest and NOx emissions are correspondingly low; in these flames, radical concentrations are high and the flame temperatures are relatively low As the pressure or residence time increases, radical concentrations are reduced and flame temperatures rise; these changes lead to an increase in the importance of the thermal mechanism with respect to the prompt mechanism. Under these conditions, the reburn process is also important. Because of the pressure dependence of nitrous oxide concentrations, the nitrous oxide mechanism is a significant contributor only at high pressures.