Effect of orifice inlet roundness on internal flow and external spray characteristics in enlarged nozzle with single-passage

Abstract

This study aims to analyze the cavitating flow inside the nozzle and the spray characteristics near the nozzle tip according to the needle positions and orifice inlet roundness through experimental analysis. To simulate the needle movement during fuel injection by the injector, six needle positions were used. The upper and lower positions of the needle were assumed to be the positions where the needle was fully opened and just before being fully closed. The length-to-width ratio of the nozzle was 2.0, and the nozzle was made in two dimensions for convenience of visualization. The inside of the nozzle was visualized by the shadow graphic visualization technique, and the image was acquired using a high-speed camera. The cavitating flow inside the nozzle and the spray characteristics near the nozzle tip were analyzed using the self-developed image processing code. The experimental results show that cavitating flow characteristics such as cavitation length and cavitation width and external flow characteristics such as spray angle were influenced by the shape of the orifice inlet and needle positions. In addition, when the cavitating flow became the hydraulic flip, the phenomenon in which the spray angle was bent like a bow was examined. This phenomenon occurred frequently as the volume fraction of hydraulic flip at the tip of the nozzle became larger than a certain level. In addition, when the cavitating flow became the hydraulic flip, the phenomenon in which the spray angle was bent like a bow was examined. In addition, we discussed the negative effects that occurring when the same phenomenon in an actual injector.