柴油机原型喷嘴内瞬态流动的特性试验

摘要

Cavitating flow in diesel injector nozzles affects the subsequent atomization behavior and spray characteristics which strongly affect diesel engine performance and emissions.Special attention was focused on the flow and spray characteristics in the real-size diesel injector nozzle based on the high pressure common rail experimental system with a high-speed digital camera and long working distance microscope.A comparative study at different pressures was conducted to analyze the evolution of cavitation inside diesel nozzle,and the experimental results show that increasing injection pressure leads to the earlier occurance of cavitation inception.The bubble "sucktion" from orifice exit at the end of injection and the bubble "discharge" at the next injection initial stage were observed.The "string cavitation" as a special cavitation phenomenon was also observed.And the occurrence of"string cavitation" has a strong correlation to the position of needle.Furthermore,the occurrence regularity of the string cavitation was also investigated.%柴油机喷嘴内的空化流动很大程度上影响燃油的雾化效果,继而影响整机的排放特性.笔者基于高速摄影技术和长工作距离显微成像技术,通过高压共轨试验系统研究原型喷嘴内的流动特性和喷雾特性.针对空化的发展进行了不同压力下的对比试验,结果表明:喷射压力越高,空化出现的时间越早,还存在喷油初期的气泡“释放”以及喷油末期的气泡“倒吸”现象;同时还观察到特殊的空化现象一线空化,并且发现线空化的出现与针阀的位置有很大关联,总结了两种不同形态的线空化发生规律.