二甲醚/乙烷混合气低温着火延迟特性

Ignition delay characteristics of DME/C2H6 mixtures at low temperatures

为了研究二甲醚/乙烷混合气在低温下的着火延迟特性,在快速压缩机实验台架上测量了二甲醚/乙烷混合气在上止点温度627~912 K,上止点压力16~30 bar,当量比0.5~1和乙烷掺混比0~70%条件下的着火延迟期.同时,基于CHEMKIN-PRO软件进行了同等工况条件下的模拟计算.实验与模拟结果表明:二甲醚/乙烷混合气总着火延迟期呈现明显的负温度系数(NTC)现象,且在较低的上止点压力下NTC现象更加明显.上止点压力和当量比的增加使得第一阶段和总着火延迟期均呈现缩短趋势,尤其在NTC区间.乙烷的添加显著抑制了着火,混合气的第一阶段和总着火延迟期显著延长.化学动力学分析表明,乙烷竞争主要由二甲醚低温着火过程主导产生的OH自由基进而抑制二甲醚的低温氧化,而自身的着火过程得到促进甚至呈现两阶段特性.但是随着乙烷掺混比的增加,整体混合气的低温着火过程仍受到抑制,放热率和活性自由基累积量降低,因此着火延迟期延长.

To investigate the ignition delay characteristics of dimethyl ether(DME)/ethane(C2H6) mixtures at low temperatures, the ignition delays were measured at compressed temperatures of 627~912 K, compressed pressures of 16~30 bar,equivalence ratios of 0.5~1 and C2H6 blending ratios of 0~70 % based on a rapid compression machine(RCM). Meanwhile, the simulation was conducted at the same conditions as those in experiments using CHEMKIN-PRO software. Both experimental and simulation results show that the total ignition delay exhibits obvious negative temperature coefficient(NTC) behavior, especially at lower compressed pressures. Increasing compressed pressure and equivalence ratio lead to decrease the first-stage and total ignition delays, especially at NTC region. C2H6 addition inhibits the ignition process significantly, thus prolongs the first-stage and total ignition delays. Chemistry kinetics analysis indicates that C2H6 competes for OH radicals predominately produced by the DME’s low-temperature oxidation, thus the ignition process of DME is delayed while the ignition process of itself is promoted and even presents evident two-stage characteristic. With the increase of C2H6 blending ratio, the ignition process of whole mixtures is inhibited, the accumulation of heat release rate and active free radicals is decreased and the ignition delays are prolonged.