Effect of Injection Pressures on Nozzle Internal Flow and Jet Breakup under Sub-cooled and Flash Test Conditions 2019-01-0286

Injection pressure paly a vital role in spray break-up and atomization. High spray injection pressure is adopted to optimize spray atomization in GDI system. At the same time, higher injection pressure also leads to engine wall wetting related emission problem. To solve this problem, researches trying to use flash boiling to dominate the spray atomization processes under lower injection test conditions. However, the effect of injection pressures on the spray atomization under flash boiling test conditions has not been adequately investigated yet. In this study, quantitative study of internal flow and near nozzle spray breakup were carried out based on a two-dimensional transparent nozzle via microscopic imaging. N-hexane was chosen as test fluid with different injection pressures. Fuel temperature varied from 63℃ to 138℃, which covered a wide range of superheated conditions. Ambient pressure was kept as 1 bar. With the experiments, the effect of injection pressures on nozzle internal flow and jet break-up is analyzed. As results, increasing injection pressures leads to better near nozzle spray break-up under sub-cooled test conditions. Under flash boiling test conditions, lower injection pressure enhances the growth of bubbles inside of the nozzle and the spray primary break-up near the nozzle. It can be inferred that although higher injection pressure can increase the spray velocity near nozzle, the primary break-up is dominated by flash boiling bubbles inside of the nozzle. The higher injection pressure leads to better secondary break-up. In practical injection system design, the optimal injection pressure can be chosen depends on spray break-up and other spray characteristics.