Detailed investigation of NO mechanism in non-premixed oxy-fuel jet flames with CH4/H2 fuel blends

This study systematically investigates the detailed mechanism of nitrogen oxides (NOx) in CH4 and CH4/H2 jet flames with O2/CO2 hot coflow. After comprehensive validation of the modeling by experiments of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147-1154]; the effects of CO2 replacement of N2, mass fraction of oxygen in the coflow (YO2), and mass fraction of hydrogen in the fuel jet (YH2) on NO formation and destruction are investigated in detail. For methane oxy-fuel combustion, the NNH route is found to control the NO formation at YO2 ≤ 3%, while both NNH and N2O-intermediate routes dominate the NO production at 3% < YO2 < 10%. When YO2 ≥ 10%, NO is obtained mainly from thermal mechanism. Moreover, in the oxy-combustion of methane and hydrogen fuel blends with YO2 = 3%, with hydrogen addition the contribution of the NNH and prompt routes increases, while that of the N2O-intermediate route decreases. Furthermore, the chemical effect of CO2 is significant in reducing NO in both oxy-combustion of methane with YO2 ≤ 3% and combustion of methane and hydrogen fuel blends with YH2 ≤ 10%.