二甲醒掺混对氨高温着火延迟期的影响

Focusing on the problem that ammonia with low chemical reactivity has difficulty achieving reliable ignition and efficient combustion in engine applications, experimental and simulation studies were conducted in the paper to understand the effects of adding active additives, namely dimethyl ether(DME), on the ignition delay times of ammonia. Firstly, experimental measurements of stoichiometric ammonia/DME mixtures were conducted in a shock tube at temperatures of 1 079—1 667 K and with a pressure of 1 MPa to reveal that DME addition can shorten the ignition delay times. Secondly, predictions of the literature chemical kinetic models on the ignition delay times of ammonia/DME mixtures were verified against the experimental results. Thirdly, chemical kinetics analyses, including reaction pathway analysis, sensitivity analysis, and free-radical ROP analysis, were carried out to understand the influence of DME addition on the ignition delay times of ammonia using the Dai model. Experimental results indicate that the addition of DME remarkably promotes the ignition delay of ammonia nonlinearly at high temperatures, revealing that only a small amount of DME addition can reduce the ignition delay times in practical applications. Chemical kinetic analysis reveals that the addition of 5% DME has a limited effect on the reaction pathway of ammonia and the two fuels compete for free radicals during the ignition; DME addition can accelerate the production rate of the OH radical in the early stage of the ignition, thus significantly shortening the ignition delay times. The research can provide a reference for the ignition improvement and performance optimization of ammonia-fueled engines.