不同燃油温度喷嘴内部流动可视化试验

Visualization of Cavitating Flow in Diesel Nozzles at Different Fuel Temperatures

柴油机喷嘴内空穴流动对喷雾有着重要影响,而燃油物性又强烈影响着喷嘴内空穴流动,因而弄清不同燃油温度下的燃油物性对喷嘴内空穴流动影响有重要的意义.在自行搭建的透明喷嘴内空穴流动自循环可视化试验台上,采用高速数码摄影和长工作距离显微成像技术,获得了不同燃油温度下喷嘴内空穴流动图像及流动特性数据.结果表明:随着燃油温度升高,空穴初生压力减小;在同样边界条件下,燃油温度越高,其雷诺数越大.对流量系数与空穴数平方根线性关系进行了修正;试验观察到了迟滞现象,为对该现象进行分析,分别定义并获得了不同燃油温度下可视化临界空穴数与定量测量临界空穴数,并发现在不同燃油温度下可视化临界空穴数都大于定量测量临界空穴数.

Spray characteristics of diesel is influenced not only by the aerodynamic force,but also by the cavitating flow in diesel nozzles which is strongly affected by fuel physical properties. It plays a critical role in the study of the effects of fuel physical properties at different fuel temperatures on cavitating flow in diesel nozzles. A visualization system with a transparent scaled-up vertical injector nozzle tip was set up. A high resolution high-speed CCD camera equipped with a long distance microscope device was used to acquire the flow images at different fuel temperatures.Results show that the critical pressure of cavitation inception decreases as fuel temperature is increased. Under the same boundary condition,higher fuel temperature corresponds to larger Reynolds number. Moreover,the relationship between discharge coefficient and square root of cavititon number was amended. To analyze the hysteresis phenomenon of the experiments,the critical cavitation number at different temperatures was further classified into the visible one and quantitatively measured one. Analysis and calculation show that the visible critical cavitation number was always higher than the quantitatively measured cavitation number under the same temperature.