NOx and N2O in lean-premixed jet-stirred flames

This study examines NOx/N2O formation mechanisms that are relevant to lean-premixed combustion in practical high-intensity combustors. Both experiments and kinetic modelling are presented. The experimental system for examining high-intensity, lean-premixed combustion is a 1-atm jet-stirred reactor. The reactor burns CH4 and CO/H2 over a fuel-air equivalence range of 0.41 to 0.67, a reactor mean residence time of 1.7–7.4 ms, and measured reactor temperature of 1415 to 1845 K. The CO/H2 fuel is used to eliminate the effects of hydrocarbon attack on the nitrogen system. The NOx mole fraction (wet) measured for the CH4 experiments correlates well with measured temperature (K) and reactor mean residence time τ (s) as follows: XNOx = τ(1.28 × 104)exp(−27230/T). Because of the enhanced O-atom concentration, the NOx mole fraction for the CO/H2 combustion is about threefold higher than for the CH4 combustion. Furthermore, because the free radical behavior in the CO/H2 experiments is complex near blowout, a simple correlation is not available. For the CH4-air experiments, chemical reactor modeling indicates that the approximate percentages of NOx production by the nitrous oxide, Zeldovich, and prompt mechanisms vary from 65:25:10 at 1650 K to 35:50:15 at 1850 K. For the CO/H2-air experiments the nitrous oxide to Zeldovich contributions vary from 95:5 at 1500 K to 65:35 at 1725 K.