Effect of Dimethyl Ether on Ignition Characteristics of Ammonia and Chemical Kinetics
The contribution of dimethyl ether(DME)to the ammonia(NH3)ignition delay time was investigated on a reflected shock wave equipment.The experiments were performed at a pressure of 0.14/1.00 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,respectively.The experimental results show that the addition of DME decreases the ignition delay time and promotes the reactivity of NH3.With DME blending,the effect of equivalence ratio on the NH3 ignition delay time is decreased,and with an increase in temperature and pressure,the effect of DME on promoting NH3 ignition is weakened.An updated mechanism was proposed to quantify DME-promoted NH3 ignition.The experimental data was validated with literature mechanisms,and the results were in line with the experimental trends under all condi-tions.Chemical kinetic analyses were performed to interpret the interactions between DME and NH3 for fuel igni-tion.Numerical analysis indicates that the promotion effect of DME is mainly due to the increase in the rate 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 are the key to the consumption of NH3 and the early initiation of the chain reaction.
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