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

Abstract

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. SL of NH3/DME/air is slightly lower than NH3 blended with DMM. SL of syngas/NH3/air flame is firstly lower and then higher than DME/NH3/air. The position of cross point is around xNH3=0.4.