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

• Published in: Energy (Oxford) 2019-05, Vol.175, p.250-258
• Main Authors: Liu, Shibo, Zou, Chun, Song, Yu, Cheng, Sizhe, Lin, Qianjin
• Format: Article
• Language: English
• Subjects: Ammonia; Carbon dioxide; Combustion; Counterflow; Equivalence ratio; Flame propagation; Flames; Fuel combustion; Laminar flame speed; Methane; NH3 oxidation; Nitrogen dioxide; Nitrous oxide; Organic chemistry; Oxidation; Oxy-fuel; Reduction; Sensitivity analysis
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2019.03.040

The laminar flame speeds of CH4/NH3 mixtures during oxy-fuel combustion conditions were measured under variable NH3/CH4 ratios (0.1–0.2), O2 mole fractions (35%–40%), and CO2 mole fractions (45%–65%) in a counterflow flame configuration (set at atmospheric pressure and unburnt mixture temperature (Tu = 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 CO2 or increasing O2 concentrations under the conditions considered, while the slopes were irrelevant for the equivalence ratio. Nevertheless, the effects of NH3 concentration depended on the equivalence ratio: the sensitivity and pathway analyses of NH3 oxidation revealed that, among the N-containing reactions in the fuel-lean region, NO oxidation and reduction (NO + HO2 = NO2+OH, NH2+NO = NNH + OH, NO2+H = NO + OH, and CH3+NO2 = CH3O + NO) had the largest impact on the laminar flame speeds. In stoichiometric region, the NO reduction pathway (NH2+NO = N2+H2O, NH2+NO = NNH + OH, NH + NO = N2O + H, and NH + NO = N2+OH) greatly contributed to flame propagation. In fuel-rich region, N + NO = N2+O and N + OH = NO + H had the biggest impact over laminar flame speeds. •The Su0 of CH4 with high concentration of NH3 in oxy-fuel combustion were measured.•The Su0 are linear dependent on O2 and CO2 concentrations.•The Su0 in fuel-lean reduce faster than that in fuel-rich due to the NH3 addition.•The oxidation and reduction of NO have the most impact on the Su0 in fuel-lean.•N + NO·N2+O and N + OH·NO + H are the most important reactions for Su0 in fuel-rich.