Study On Internal Flow And Spray Characteristics Of GDI Injector

The spray structure determines the fuel distribution and mixture formation, andthen has a direct impact on the combustion, so GDI injector is a major component ofthe GDI combustion system. Furthermore the spray is essentially affected by thecavitation phenomenon inside the nozzle holes. The phenomenon of cavitation mainlyhas a great impact on the velocity, mass flow, and turbulent kinetic energy distributionat the nozzle exit. The cavitation is the one of dominant factors causing primarybreakup, so the internal nozzle flow must be considered in the design of GDI engine.Theoretical and experimental studies have both proved that: high-pressure dieselinjection nozzle is easy to form cavitation. In recent years, some scholars find that GDImulti-hole injector will also have cavitation in the injection process. Compared todiesel nozzle, the study of the cavitation inside the GDI nozzle is still not enoughcurrently. As the nozzle flow is an unstable gas-liquid two-phase flow, and the nozzlestructure also impedes the experiments to observe the nozzle flow directly, so thesimulation become an important research method of internal flow.This paper using two-fluid method simulate the internal flow of GDI multi-holeinjector at the maximum needle lift, besides the results predict whether or not thecavitation would occur and discuss the uneven flow between the six nozzle holes. Thestudy on cavitation distribution inside nozzle with needle valve lift movement is alsoput on. At the same time, the data of the internal flow calculation with needlemovement is gained and will be used as a boundary condition for the subsequent spraycalculation. The data contains the values of the liquid velocities, densities and theturbulence quantities at nozzle’s outlet. During the spray simulation, the data isintroduced by using different initial breakup model and the effects of internal flow onspray characteristics are also been analyzed qualitatively.