The effect of the divergent-convergent GDI injector on inner flow and spray characteristics at high injection pressure

Abstract

ABSTRACT The effects of Divergent-Convergent (D-C) nozzle parameters on the inner flow and spray characteristics of GDI (Gasoline Direct Injection) injector were studied under the condition of high injection pressure of 40 MPa. Homogeneous Relaxation Model (HRM) was used to explore the GDI orifice inner cavitation flow and nozzle exit flow parameters. A one-way coupled spray model was adopted to study the GDI spray behaviors. From these results, the cavitation density in the orifice decreases with the increase of the medium diameter ratio Km, while the discharge coefficient and the orifice exit velocity increases with the increase of Km. Moreover, the nozzle exit average velocity increases with the increase of Xm, and the nozzle exit average velocity with the Km of 1.5 is about 14.1% larger than that of the cylindrical nozzle. While the changing of the Xm has no effect on the nozzle exit average velocity for the same median diameter ratio. Additionally, the turbulent kinetic energy at the nozzle exit decreases with the increase of Km, especially the turbulent kinetic energy for the D-C nozzle with Km of 1.5 is about 17.1% smaller than that of the cylindrical nozzle. In addition, the D-C nozzle with Xm of 0.5 held the smallest turbulent kinetic energy. Also, the Sauter Mean Diameter (SMD) decreases with the decrease of Km at the initial injection stage. However, the spray SMD increases with the decrease of Km, and the SMD decreases with the increase of Xm at the late injection stage. Furthermore, the SMD of D-C nozzle is smaller than that of the cylindrical nozzle at the late injection stage.