COMPARISON BETWEEN A CENTER-MOUNTED AND A SIDE-MOUNTED INJECTOR FOR GASOLINE APPLICATIONS: A COMPUTATIONAL STUDY

摘要

The differences between a center-mounted and a side-mounted injector for gasoline direct injection (GDI) applications are analyzed through computational fluid dynamics (CFD). The Engine Combustion Network's (ECN) axisymmetric 8-hole Spray G injector is compared to a 6-hole injector designed to be side-mounted in an engine. Nozzle-flow simulations are carried out with the commercial CFD software CONVERGE, injecting Euro 5 certification gasoline into a constant volume chamber. Low-load operating conditions are targeted, setting the injection pressure at 50 bar and the ambient pressure to be representative of very early pilot injections. The phase change is handled with the Homogeneous Relaxation Model (HRM), which is assessed and adapted to gasoline flash-boiling conditions. The simulation domains are generated leveraging real injector internal geometries obtained by micron-resolution X-ray tomographic measurements, which introduce manufacturing tolerances and surface roughness in the computational study Steady needle lift conditions are analyzed. The near-field fuel density distributions and plume morphologies are evaluated, validated and compared to X-ray radiography measurements. A computational best practice is defined and single plume characteristics and variability trends are highlighted as functions of the geometry of the orifices. The plume-plume interaction dynamics are identified and assessed, underlining differences from center- to side-mounted injectors at strong flashing conditions. The obtained numerical framework allows the identification of near-nozzle injection characteristics such as single plume direction,cone angle, spray initial velocity and spatial fuel density distribution. The presented results represent a unique dataset for the initialization of more-affordable Lagrangian spray models, which differentiate the behavior of side-mounted and center-mounted injectors.