However the previous study focused on only the flow in the discharge hole under the steady flow condition. Therefore the main objectives of the present study are as follows:
(1) To clarify the effects of the flows in the sac chamber and the discharge hole on the spray behaviors during the opening and closing processes of the needle vale.
(2) To characterize the internal flows of various types of D.I. Diesel nozzles and their issued spray behaviors.
In order to achieve these objectives, high-speed video observation of the flows in the sac chamber and the discharge hole was made using ten times scale up and transparent model nozzles, which were based on the geometries of hole type D.I. Diesel nozzles. High-speed video observation was also made of the sprays issued from the model nozzles.
2. EXPERIMENTAL APPARATUS AND PROCEDURES
2.1 Injection System and High-Speed Video Observation
Figure 2 shows a schematic diagram of the experimental apparatus. Water instead of a Diesel fuel was used as the injection liquid. In the beginning of the experiment, the needle valve was pressed down by the lever. After the injection pressure was adjusted, the needle valve lever was released and the injection initiated. The injection pressure was set at 0.2 MPa. The vertical cross sectional area in the sac chamber including the nozzle axis was illuminated from the bottom side of the sac chamber by a light sheet with 1 mm thickness from an Ar+ laser. Aluminum oxides under the 325 meshes were used as flow tracers. Sequential images of the flow pattern in the light sheet plane of the sac chamber were taken by a high-speed video camera during the needle valve opening process. Sequential images of the issued spray and the cavitation in the sac chamber and the discharge hole during the needle valve opening and closing processes were taken by the high-speed video camera and the diffusion light illumination without mixing the flow tracers into the injection water.
2.2 Model Nozzles
Five kinds of transparent acrylic model nozzles, such as Standard (STD) Model I, STD Model II, STD Model III, Mini Sac Model and Valve Cover Orifice (VCO) Model were used in this study. Typical results of the STD Model I, III, the Mini Sac Model and the VCO Model are described in this paper.
Figure 3 shows the configurations of the model nozzles. Each nozzle has two discharge holes with an injection angle of 157 degrees. The diameter and length of each hole is dh = 2 mm and Ih = 8 mm, respectively. For all model nozzles, the needle valve has a conical tip with an angle of 60 degrees.
Fig.4 Variations of Cross Sectional Areas of Flow Passages in Model Nozzle with Needle Lift
