Characteristic Analysis of High-Pressure Common-Rail Injector Nozzles

Abstract

This study investigates an SAC-type injector nozzle used in a diesel high-pressure common-rail fuel-injection system. The mixture multiphase-flow model, RNG k-ε turbulence model, and Schnerr–Sauer cavitation model were employed to compare the internal flow characteristics of circular and elliptical nozzle orifices under different operating and geometric parameters. The results show that, as the inlet pressure increased from 110 to 170 MPa, the outlet velocity and mass flow rate of the elliptical orifice reached 495.80 m/s and 27.28 g/s, respectively, while the outlet vapor volume fraction increased to 0.161. As the outlet back pressure increased from 5 to 20 MPa, the outlet vapor volume fraction of the elliptical orifice was 41.32–46.49% lower than that of the circular orifice, whereas its mass flow rate was 4.84–23.54% higher. The geometric-parameter analysis indicated that superior internal flow performance was obtained at a nozzle-orifice angle of 75° and an inlet rounding radius of 0.03 mm. The converging elliptical orifice increased the outlet velocity and mass flow rate by 18.3% and 23.29%, respectively. These results demonstrate that the converging elliptical orifice can effectively mitigate flow separation and cavitation while improving outlet-flow uniformity and fuel-delivery performance.