基于背压的柴油机喷嘴内部空穴流动试验研究

Experimental Research of Cavitating Flow in Diesel Fuel Injector Nozzle under Different Back Pressures

在自行搭建的比例放大透明喷嘴内部流动可视化试验台上,采用高速数码摄像和长工作距离显微成像技术,研究了不同背压条件下喷嘴喷孔内部单相流及空穴两相流的流动特性。研究结果表明:喷油压力一定时,背压逐渐升高会使喷孔内的空穴分布区域逐渐减小,直至消失,流动也由空穴两相流转变为单相流;较高的背压会增加空穴初生的难度,空穴初生对喷孔前后压差要求也更高,同时喷孔出口的燃油平均速度也更高;相同压差下,较高的背压对单相流阶段造成的流动损失较大,对空穴两相流阶段造成的损失则较小。

A flow visualization experiment system with a transparent scaled-up injector nozzle was set- up and flow characteristics of both single-phase flow and two-phase cavitating flow in the nozzle under differ- ent back pressures were studied with a high speed video camera coupled with a long-distance microscope. The experimental results show that when injection pressure reaches certain level, cavitation area in nozzle shrinks and even disappears with the gradual increase of back pressure, and the flow changes from two-phase cavitat- ing flow to single-phase flow. Under higher back pressure, cavitation in the nozzle is harder to generate, the pressure difference for generating cavitation is larger and the mean fuel velocity at the nozzle outlet is also larger. Under the same pressure difference, higher back pressure causes larger flow loss in a single-phase flow than in two-phase cavitating flow.