Numerical Investigation of GDI Injector Nozzle Geometry on Spray Characteristics

摘要

The large eddy simulation (LES) with Volume of Fluid (VOF) interface tracking method in Ansys-FLUENT has been used to study the effects of nozzle hole geometrical parameters on gasoline direct injection (GDI) fuel injectors, namely the effect of inner hole length/diameter (L/D) ratio and counter-bore diameters on near field spray characteristics. Using iso-octane as a model fuel at the fuel injection pressure of 200 bar, the results showed that the L/D ratio variation of the inner hole has a more significant influence on the spray characteristics than the counter-bore diameter variation. Reducing the L/D ratio effectively increases the mass flow rate, velocity, spray angle and reduces the droplet size and breakup length. The increased spray angle results in wall impingements inside the counter-bore cavity, particularly for L/D=1 which can potentially lead to increased deposit accumulation inside fuel injectors. The influences of the counter-bore diameter become more obvious with decreased L/D ratio. For the lower L/D ratio, the sprays with large included angles are more vulnerable to the air entrained into the counter-bore cavity and the recirculation flow inside it. Increasing the counter-bore diameter has an overall adverse effect on the spray characteristics as the spray exits the counter-bore. Flow rates and spray angles decrease and droplet sizes are increased with increased counter-bore diameters for any given L/D ratio. The positive recirculation inside the small diameter counter-bores improves the mass flow rate from the inner hole. Inside the counter-bore cavity and further downstream from it, large interconnected ligaments are present which undergo deformation and secondary breakup.