Large Eddy Simulation of GDI Single-Hole Flow and Near-Field Spray

The improvement of spray atomization and penetration characteristics of GDI multi-hole injector sprays is a major component of the engine combustion developments, in order to achieve the fuel economy and emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to achieve optimum multiobjective spray characteristics. The Volume-of-Fluid Large-Eddy-Simulation (VOF-LES) of the injector internal flow and spray break-up processes offers a computational capability to aid development of a fundamental knowledge of the liquid jet breakup process. It is a unique simulation method capable of simultaneous analysis of the injector nozzle internal flow and the near-field jet breakup process. Hence it provides a powerful toll to investigate the influence of nozzle design parameters on the spray geometric and atomization features and, consequently, reduces reliance on hardware trial-and-tests for multi-objective spray optimizations. This publication reports investigations of a single, axisymmetric nozzle-hole, pertinent to GDi multi-hole injector nozzle geometry, with the aid of the current state-of-the-art VOF-LES method. The focus of the study is the influence of nozzle degsign and geometric features on the plume structure and its primary break-up process. Specifically, the influence of nozzle length-to-diameter ratio ( l/d), counter-bore, and nozzle tapered geometry on the jet primary breakup are studied. Analysis of alternative nozzle geometries reveal the influence of marked influence of nozzle shape and l/d ratio on the nozzle flow structure, hydraulic efficiency and the jet breakup characteristics. There is marked influence of flow separation and hydraulic flip in the nozzle hole for amplification of the Kelvin-Helmholtz instabilities and the jet breakup length.