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

The formation/destruction mechanisms of nitric oxides (No-x) in CH4/H-2 jet flames in a hot coflow are systematically investigated by numerical modeling. All calculations use the Eddy Dissipation Concept (EDC) model coupled with GRI-Mech 2.11. The modeling is validated by the measurements of Daily et al. [Proc. Combust. Inst. 29 (2002) 1147-1154]. Dependences of the NOx formation/destruction routes on Y*O-2, T*(cof) and Y*(H2), are examined, where Y*O-2, T*(cof) and Y*(H2) are the coflow oxygen concentration and temperature, and the hydrogen fraction in the fuel mixture, respectively. The following is obtained. For Y*O-2 <= 3% at T*(cof) = 1300 K and Y*(H2) = 12%, the N2O-intermediate, prompt and NNH routes are the first (approximate to 50%), second (30%) and third (20%) contributors to the total NO emission; asY*O-2 is increased, the contributions of the three routes all decrease whereas that of the thermal route becomes significant. For Yo*2 = 3% and YH*2 = 12%, the N2O-intermediate route dominates the NO formation (about 90%) at T*(cof) < 1000 K; as T*(cof) is increased from 1000 K, the importance of either the prompt, NNH, or thermal routes is enhanced. For Y*O-2 = 3% and T*(cof) = 1300 K, as Y*(H2) 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 Y*O-2, T*(cof) and Y*(H2), or altogether is found to strengthen the importance of NO2 to the total NOx emission and the NO-reburning. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.