Experimental and kinetic study on laminar flame speeds of ammonia/dimethyl ether/air under high temperature and elevated pressure

Laminar flame speeds of ammonia mixed with dimethyl ether (DME) under elevated pressure and high temperature at different equivalence ratios were measured. Several kinetic models (Dai model, DTU model, Shrestha model, Mei model, Zhang model and Han model) are compared and validated with experimental data. Models with best performance were combined together for NH₃/DME laminar flame speed validation and Dai-Zhang model was obtained. Simulations from Dai-Zhang model match well with experimental data. Pathway, sensitivity and key radicals’ mole fraction analysis were conducted to find out the deep kinetic insight on ammonia oxidation with and without DME addition. With DME addition, the oxidation of NH₂ radical is dominated by carbon-containing species, with roughly NH₂ 50% reacting via NH₂ + CH₂O = NH₂ + CHO and NH₂ + CH₃ = CH₃NH₂. In NH₃/air flame, NH₂ and NH radicals’ recombination reactions are more dominant than that in NH₃/DME/air flame. Abstraction of NH₂ by OH and H radicals forming NH becomes more important while branching ratio of HNO formation decreases. The directly oxidization of NH yielding NO can be neglected. Thus, NO formation decreases remarkably and the laminar flame speed is lower than co-firing with DME. Comparison was also conducted in NH₃/DME/air, NH₃/DMM/ air and NH₃/syngas/air flames. S_L of NH₃/DME/air is slightly lower than NH₃ blended with DMM. S_L of syngas/NH₃/air flame is firstly lower and then higher than DME/NH₃/air. The position of cross point is around x_NH3=0.4.