柴油机模型喷孔内空化与空蚀特性试验研究

Experiment on Characteristics of Cavitation and Erosion in Diesel Engine Nozzle Orifice

在真实喷油器空蚀试验基础上,利用X射线CT扫描检测到了喷嘴内微量空蚀。为获得空化对空蚀的具体影响,搭建了可同时获得喷孔内空化区域和空蚀区域及形貌的可视化试验装置,采用高速摄影技术和电镜扫描(SEM)技术,针对一个矩形喷孔内空化流动和空蚀特性进行试验研究。结果表明:喷射压力越高,喷孔内空化发展越充分,并出现了单相流、不完全空化流、超空化流和水力回流4种不同流态;云空化脱落呈现出一定的循环周期性,且喷孔下游空蚀区与云空化脱落溃灭区非常吻合。结合壁面附近空化区与液相区交界处存在的空蚀现象,推理云空化脱落溃灭和冷凝溃灭是喷孔内空蚀形成的两大因素。

Based on the cavitation erosion test of a real injector,the micro cavitation erosion in the injector nozzle was detected by X-ray CT scanning.To obtain the specific influence of cavitation on erosion,special attention was made on the characteristics of cavitating flow and cavitation erosion in a simplified rectangle nozzle orifice based on a self-circulation visualization experimental setup that can obtain cavitation area,erosion area and morphology at the same time as well as with a high-speed digital camera and the scanning electronic microscopy technology(SEM).The results show that with the increase of injection pressure,cavitation grows more intensely,and four different flow states appear in succession:single-phase flow,incomplete cavitating flow,super-cavitating flow,and hydraulic flip.The cloud cavitation shedding shows a certain cyclic periodicity.The cavitation erosion region at the downstream of the nozzle orifice appears in the area of cloud cavitation shedding and collapsing,and the cavitation erosion phenomenon exists at the junction of cavitation and liquid phase.It can be reasoned from the results that the cloud cavitation shedding and collapsing as well as condensation collapsing are two main factors of cavitation erosion.