Techniques for analyzing swirl nozzles of direct-injection gasoline engines and application to tapered tip nozzle analysis

This paper describes the numerical and experimental approaches that were applied to study swirl nozzles that are widely used in direct-injection gasoline engines. As the numerical approach, the fuel and air flow inside a nozzle was first analyzed by using a two-phase flow analysis method employing a volume of fluid (VOF) model. Spray droplet formation was then analyzed with a discrete droplet model (DDM). As the experimental approach, particle image velocimetry (PIV) was used to measure the spray velocity distribution. These approaches were applied to test nozzles, having a tapered tip geometry at the nozzle exit. The spray shapes produced by the nozzles were skewed to the tapered side. Additionally, the cone angle of the spray on the skewed side did not change very much even under a condition of high ambient pressure. The analysis results suggest that the skewed spray shapes are influenced mainly by the spray cone angle and circumferential fuel mass distribution at the nozzle exit.