二甲醚在低到中温的着火延迟特性

Ignition delay characteristics of dimethyl ether under low-to-medium temperature ranges

在上止点温度656～814 K,上止点压力1.2～3.5 MPa,当量比(φ)0.83～1.25实验条件下,利用快速压缩机(RCM)研究了上止点压力和燃料浓度对二甲醚着火延迟期的影响及二甲醚三阶段燃烧现象。利用CHEMKIN-PRO软件在更宽广温度范围内对混合气着火延迟进行了同等条件下的模拟计算及反应动力学分析。结果表明:随着上止点压力及燃料浓度的增加,第1阶段着火延迟期均略有缩短,总着火延迟期明显缩短;二甲醚总着火延迟期存在明显的负温度系数(NTC)现象,且在较低上止点压力和燃料浓度下NTC现象更加明显;在稀燃条件下(φ(28)0.83)二甲醚混合气出现低温放热和高温两阶段放热的三阶段放热现象,其高温第1阶段放热主要由CH_2O生成大量CO引起,高温第2阶段放热主要由生成燃烧最终产物CO_2和H_2O引起。

Effects of the compressed pressure and fuel concentration on ignition delay of DME mixture were investigated using a rapid compressor at compressed temperature of 656--814 K, compressed pressure of 1.2--3.5 MPa and equivalence ratio （φ） of 0.83--1.25. Kinetics model was built to predict the ignition delay and simulate the combustion process using CHEMKIN-PRO software, meanwhile, reaction kinetics analysis was conducted. The results show that with increasing compressed pressure and fuel concentration, the first-stage ignition delay decreases slightly, while a significant decrease in the total ignition delay is observed. The ignition delay of DME presents well known negative temperature coefficient （NTC） and which is noted to become more prominent at lower compressed pressure and fuel concentration. DME mixture presents three-stage heat release at lean-fuel （φ = 0.83 ） , which includes low-temperature heat release and a two-stage high temperature heat release. Kinetics analysis indicates that the first-stage high temperature heat release is mainly caused by the production of CO from CH20, and the reactions produce CO2 and H20 contribute to the second-stage high temperature heat release.