柴油机喷嘴内部流动可视化试验

Visualization Experiment of Cavitation Flow in Diesel Nozzles

柴油机喷雾特性除受空气动力作用影响外,更与喷嘴内空穴流动有关,因此弄清喷孔内空穴流动对研究喷雾特性有着至关重要的作用.在自行搭建的比例放大透明喷嘴内空穴流动可视化试验台上,采用高速数码摄影和长工作距离显微成像技术,获得了不同几何结构喷嘴内部空穴流动图像.试验结果表明,不同的几何结构对喷嘴内空穴流动有着强烈的影响,增大喷孔长度和减小喷孔与喷嘴轴线间夹角都能抑制喷孔内空化现象,而采用VCO类型喷嘴可使发生水力柱塞流的压力更高;试验还观察到了迟滞现象.

Spray characteristics of diesel is not only influence by the aerodynamic force, but also by the cavitation flow in the diesel nozzle. It plays a critical role to study the spray characteristics for understand- ing the detail cavitation flow in diesel nozzles. In this paper, a flow visualization experiment with a transparent scaled-up vertical injector nozzle tip was setup. A high speed CCD camera equipped with long distance microscope device was used to acquire the flow images with different geometries. Results show that the geometry has a strong impact on the cavitation flow of the inner nozzle. Cavitation phenomenon is suppressed by increasing the length of nozzle hole and decreasing the angle of nozzle axis. High hydraulic flip pressure is produced using VCO type nozzle. Increasing the pressure drop significantly intensifies the cavitation phenomenon. Hysteresis cavitation phenomenon was observed in the experiment.