An Investigation on Droplet Size Distribution and Evaporation of Diesel Fuel Sprays at High Injection Pressure by Using Laser Diagnostic Technique 920090

A series of experimental studies on the diesel fuel spray characteristics were carried out in a constant volume bomb. The bomb was charged with nitrogen gas and equipped with quartz windows for using the laser diffraction instrument and with a reconstructed CUMMINS PT system for getting a single shot injection of fuel at an injection pressure as high as 130 MPa. A heater within the bomb enables the temperature of the charge to be increased to 800 K. A Malvern 2604C Particle Sizer based on Fraunhofer diffraction principle was used to measure the size distribution of the fuel droplets. The main results obtained in this paper show that the SMD (Sauter Mean Diameter is the diameter of a droplet whose ratio of volume to surface area is equal to that of the entire spray) of a spray at high injection pressure is much smaller than that at ordinary injection pressure and with the temperature rising, the smaller droplet fraction of the total decreases and the SMD increases. Although the ambient temperature reaches 800 K, there are still unevaporated droplets to be observed. When the spray jet impinges on the wall, the SMD of rebounded droplets is dependent on the space position. After the injection stopped, a spray tail which contains a large volume fraction of big drops was observed. It may be one of the imperfect combustion sources in spray flames and plays an important role on the combustion characteristics.