聚甲氧基二甲醚-甲醇混合燃料的燃烧与排放特性研究

将甲醇按体积比0、10%、20%、30%分别掺混到聚甲氧基二甲醚(polyoxymethylene dimethyl ethers,PODE)中制备出PODE-甲醇混合燃料,并依次标记为M0、M10、M20和M30,在一台高压共轨发动机上研究了最大转矩转速不同负荷下混合燃料的缸内燃烧过程和排放性能。结果表明:在PODE中添加甲醇后,各负荷下缸内压力降低,滞燃期逐渐延长,放热始点推迟。低负荷和中负荷时甲醇体积比的增加会使放热率峰值先增加后减小,而高负荷下放热率峰值却逐渐升高。甲醇体积比较低时,各负荷下燃烧持续期缩短;当甲醇体积比为30%时,中低负荷下燃烧持续期延长,各负荷下燃烧重心(CA50)推迟。掺烧甲醇可以降低NO_x浓度,M30较M0降低幅度为28.1%;而随甲醇体积比的增加,各负荷下HC和CO排放量均呈上升趋势,烟度则先减小后增大。甲醇的低温氧化使混合燃料的甲醛排放量上升,同时NO_2排放量及NO_2占NO_x比例随甲醇体积比的升高而增加,与纯PODE相比,低负荷下M30的NO_2排放量和NO_2占NO_x比例增幅分别为65%和107%。

Investigation on Combustion and Emission Characteristics of Polyoxymethylene Dimethyl Ethers-Methanol Blends

According to the volume fraction of 0, 10%, 20% and 30%, methanol was blended into polyoxymethylene dimethyl ethers (PODE) to prepare the PODE-methanol blends and marked as M0, M10, M20 and M30, respectively. The combustion and emission performance of a high pressure common rail diesel engine under different load at maximum torque speed was studied. Results show that when methanol is added into PODE, the in-cylinder pressure decreases and the ignition delay period is gradually prolonged. With the increase of methanol ratio at light and medium loads, the peak value of heat release rate increases first and then decreases, while at heavy load, the peak value of heat release rate increases gradually. When methanol ratio is low, the combustion duration is shortened under various loads. When the methanol ratio reaches 30%, the combustion duration is extended under light and medium loads, and the heat release center (CA50) is delayed under various loads. With the increase of methanol ratio, the emission of NOx decrease at each load while the emission of HC and CO increase, and the smoke emission decrease first and then increase. Formaldehyde emission increase gradually due to the low temperature oxidation of methanol. At the same time, the NO2 emission and NO2/NOx ratio increase with the increase of methanol ratio. Compared with pure PODE, the increase of NO2 emission and NO2/NOx ratio of M30 under light load are 65% and 107%, respectively.