Experimental and numerical study of laminar flame speeds of CH4/NH3 mixtures under oxy-fuel combustion

Abstract The laminar flame speeds of CH 4 /NH 3 mixtures during oxy-fuel combustion conditions were measured under variable NH 3 /CH 4 ratios (0.1–0.2), O 2 mole fractions (35%–40%), and CO 2 mole fractions (45%–65%) in a counterflow flame configuration (set at atmospheric pressure and unburnt mixture temperature (T u  = 300 K)). These experimental results were compared to the numerical results obtained through three detailed chemical kinetic mechanisms: the Okafor, Mendiara and HUST (Huazhong University of Science and Technology) mechanisms. The comparisons showed that the results obtained through the HUST Mechanism were in good agreement with the experimental results. The experimental results showed that the laminar flame speeds increased linearly with decreasing CO 2 or increasing O 2 concentrations under the conditions considered, while the slopes were irrelevant for the equivalence ratio. Nevertheless, the effects of NH 3 concentration depended on the equivalence ratio: the sensitivity and pathway analyses of NH 3 oxidation revealed that, among the N-containing reactions in the fuel-lean region, NO oxidation and reduction (NO + HO 2  = NO 2 +OH, NH 2 +NO = NNH + OH, NO 2 +H = NO + OH, and CH 3 +NO 2  = CH 3 O + NO) had the largest impact on the laminar flame speeds. In stoichiometric region, the NO reduction pathway (NH 2 +NO = N 2 +H 2 O, NH 2 +NO = NNH + OH, NH + NO = N 2 O + H, and NH + NO = N 2 +OH) greatly contributed to flame propagation. In fuel-rich region, N + NO = N 2 +O and N + OH = NO + H had the biggest impact over laminar flame speeds.