二甲基醚(DME)燃烧特性研究

摘要

作者在定容燃烧弹上用火焰直接成像法研究二甲基醚(DME)燃烧过程，研究了DME的滞燃期和火焰传播特性以及不同环境温度和压力对燃烧过程的影响。研究结果表明，DME的滞燃期比柴油短，燃烧室内的温度和压力升高时，滞燃期缩短；DME的着火位置靠近喷嘴一侧，柴油与DME的体积相同时，DME的燃烧持续期比柴油短；DME的燃烧火焰亮度比柴油小，表明DME的燃烧温度比柴油低。燃烧后期，燃用DME时，喷嘴有明显的泄漏现象。此外，作者在单缸直喷式柴油机上进行了燃用DME的燃烧特性试验研究，研究结果表明，DME的预混合燃烧放热率比柴油低，缸内最大爆发压力和最大压力升高率比柴油低。由于喷油持续期延长，DME的燃烧持续期比柴油长，在上止点后80° CA出现一个较大的放热峰值。%In this paper,the effects of the ambient temperature and pressure on the DME ignition and combustion processes were investigated.The results show that the ignition delay of DME is shorter than that of diesel fuel.With increasing in the ambient temperature and pressure,the ignition delay of DME becomes shorter.However,when the ambient temperature is above 973 K,there are little influences of ambient temperature and pressure on the ignition delay.The ignition position of DME is close to the nozzle,and with increasing in the ambient temperature and pressure,this position is closer to the nozzle.When the fuel delivery amounts of DME and diesel in volume are the same,the combustion duration of DME is shorter than that of diesel fuel,and the flame temperature of DME is lower than that of diesel.At the end of combustion,it was found that there was a weak light near the nozzle,it indicates that the nozzle had leakage at high temperature environment.It may be a reason that HC and CO emissions with DME are higher than those of diesel operation.In addition,the combustion characteristics of DME in a single-cylinder D.I diesel engine are also investigated.The results show that the rate of pressure rise and peak pressure in cylinder mere much lower for the DME.This will achieve lower engine noise for the DME than for the diesel.The heat release analysis results show that the maximum rate of heat release in the initial,premixed combustion phase for the DME is smaller than for the diesel,and after the initial phase,the rate of heat release is greater for the DME than the diesel.A peak value of the rate of heat release at 80° CA ATDC can also be observed,this is most likely due to the longer injection duration or secondary injection for the engine operating on DME.