Routes of formation and destruction of nitrogen oxides in CH4/H2 jet flames in a hot coflow

For YO2∗≤3% at Tcof∗=1300K and YH2∗=12%, the N2O-intermediate, prompt and NNH routes are the first (≈50%), second (30%) and third (20%) contributors to the total NO emission; as YO2∗ is increased, the contributions of the three routes all decrease whereas that of the thermal route becomes significant. For YO2∗=3% and YH2∗=12%, the N2O-intermediate route dominates the NO formation (about 90%) at Tcof∗<1000K; as Tcof∗ is increased from 1000 K, the importance of either the prompt, NNH, or thermal routes is enhanced. For YO2∗=3% and Tcof∗=1300K, as YH2∗ is elevated, the contribution of the NNH route to the total NO production increases while those of the N2O-intermediate and prompt routes decrease. Also, in general, the reduction of YO2∗, Tcof∗ or YH2∗, or altogether is found to strengthen the importance of NO2 to the total NOx emission and the NO-reburning.