喷嘴内燃油空化及影响因素的实验研究

柴油机燃油喷射雾化过程除受湍流和环境气体的空气动力学效应影响外,还与喷孔内空化有关,因此对喷孔内燃油空化和影响因素的研究有重要的意义。本文中设计了透明喷孔代替原柴油机喷油器的喷孔,采用高速数码相机和高放大倍数、高分辩率的长距离显微成像技术和纳秒级闪光灯作为相机曝光光源,获得了较高分辩率和清晰度的实验图像。对柴油机喷孔内燃油空化产生、发展和分布状态进行显微观测,直观展现喷孔内燃油空化及影响规律,获得了燃油空化过程的直观认识。结果表明,柴油机喷孔内空化流动情况比较复杂,影响因素较多,其中喷孔几何结构对喷嘴内空化过程影响最显著,喷孔内空化首先出现在压力室针阀附近,随后空化区域向喷孔出口处扩散、延伸,对于渐缩喷孔,空化形成受到抑制,而渐扩喷孔则有利于空化形成;减小喷孔直径,不利于空化形成。环境压力对空化起到抑制的作用,环境压力增大,也不利于空化形成。此外还对喷孔内空化强度进行量化描述,通过空化强度对实验获得的图像进行量化分析。

Experimental Research on Nozzle Fuel Cavitation and the Influencing Factors

Atomization of diesel engine fuel injection is not only influenced by the turbulence and aerodynamic force effect of ambient gas,but also related to the cavitation in the nozzle.Therefor,it is of great importance to study the fuel cavitation in the nozzle and the influencing factors.A transparent nozzle is designed to replace the original injector of the diesel engine.With a nanosecond level flash lamp as the exposure light source,the high speed digital camera and the high-magnification,high-resolution long-distance micro imaging technology,the experimental images with high resolution and clarity are obtained.The generation,development and distribution of fuel cavitation in the nozzle of diesel engine are observed.The fuel cavitation in the nozzle and its influence law are visually presented and a direct understanding of the process of fuel cavitation is obtained.The results show that the cavitation flow in the nozzle is complex and has many influencing factors,among which the geometry of the nozzle has the most significant influence on the cavitation process.The cavitation in the nozzle first appears near the needle valve of the pressure chamber,and then the cavitation area spreads and extends to the outlet of the nozzle.For the gradually shrinking nozzle,the cavitation formation is inhibited,while the gradually expanding nozzle is conducive to the cavitation formation.Reducing the diameter of the nozzle is not conducive to cavitation.The environment pressure has inhibiting effect on cavitation and the increase of environmental pressure is not conducive to the formation of cavitation.In addition,the cavitation intensity in the nozzle is described quantitatively,and the image obtained from the experiment is analyzed quantitatively through the cavitation intensity.