Effect of transient needle lifts on the internal flow and nozzle exit characteristics for elliptical gasoline direct injection nozzle

Abstract

This research presents the first systematic investigation into the impact of needle valve lift on cavitation flow within the nozzle orifice and outlet flow parameters of Gasoline Direct Injection (GDI) elliptical injectors, utilizing both experimental and numerical methods. The findings reveal that, in comparison to circular injectors, elliptical injectors display distinct asymmetric cavitation patterns under varying needle valve lifts, exhibiting overall lower cavitation intensity and reduced sensitivity to lift variations. A reduction in needle valve lift results in a significant increase in Turbulent Kinetic Energy (TKE) within the nozzle orifice, an effect particularly pronounced in circular injectors. In contrast, elliptical injectors generally demonstrate lower turbulent kinetic energy, mitigating the adverse effects of turbulent disturbance on flow and thereby enhancing overall flow performance. Consequently, under comparable operating conditions, elliptical injectors show markedly higher mass flow rates and discharge coefficients than their circular counterparts. Furthermore, due to their asymmetrical structure, elliptical injectors generate stronger vortex flow at the nozzle outlet, with vorticity magnitude substantially exceeding that of circular injectors. An increase in needle valve lift further amplifies vorticity magnitude, particularly in elliptical injectors. The high vorticity magnitude observed suggests the potential for elliptical injectors to further improve atomization quality, potentially leading to enhanced engine combustion and emission performance.