Effect of dimethyl ether on ignition characteristics of ammonia and chemical kinetics

The contribution of dimethyl ether(DME) to the ignition delay times(IDTs) of ammonia(NH3) was investigated behind reflected shock waves. The experiments were performed at a pressure of 0.14/1.0 MPa, temperature range of 1150-1950 K, equivalence ratio of 0.5/1.0/2.0, and NH3/DME mixing ratios of 100/0, 95/5, 90/10, and 70/30. It was observed that the addition of DME decreased the IDTs and promoted the reactivity of NH3. With the increase of DME, the effect of the equivalence ratio on the IDTs of NH3 decreased. Under higher temperature and pressure conditions, the promoting effect of DME on the ignition of NH3 was weakened. An updated mechanism is proposed to reveal the promoting effect of DME on the ignition of NH3. Mechanisms from the literature were compared against the measurements, and the updated kinetic mechanism was validated with experimental data. Good agreement between measurements and simulations were shown. Chemical kinetic analyses were performed to interpret the interactions between DME and NH3 during fuel ignition. The numerical analysis indicated that the promotion effect of DME is primarily due to an increase of the rate of production and concentration of the radical pool, especially the OH radical pool. The large number of OH radicals generated by the reaction HO2 + CH3 = OH + CH3O during the early oxidation of DME is key to the NH3 consumption and early initiation of the chain reaction.