Development of in-cylinder spray targeting, plume penetration and atomization of the gasoline direct-injection (GDi) multi-hole injector is a critical component of combustion developments, especially in the context of the engine downsizing and turbo-charging trend that has been adopted in order to achieve the European target CO2, US CAFE, and concomitant stringent emissions standards. Significant R&D efforts are directed towards the optimization of injector nozzle designs in order to improve spray characteristics. Development of accurate predictive models is desired to understand the impact of nozzle design parameters as well as the underlying physical fluid dynamic mechanisms resulting in the injector spray characteristics.
This publication reports Large Eddy Simulation (LES) analyses of GDi single-hole skew-angled nozzles, with β=30° skew (bend) angle and different nozzle geometries. The objective is to extend previous works to include the effect of nozzle-hole length over diameter ratio (l/d) and fuel injection pressure on spray skew angle, spray plume cone angle and primary breakup length. The authors provide an LES analyses of a single hole nozzle representative of the a purpose-designed GDi multi-hole injector seat. The simulations are confirmed by comparison with the spray near-field breakup structure obtained through optical shadowgraphy and phase-contrast X-ray imaging techniques.
The jet morphology indicates turbulent structures and primary atomization in the immediate vicinity of the nozzle exit. Nozzle l/d reduction produced a notable increase of plume cone angle and spray trajectory deviation (from geometric nozzle axis). The analyses provide insight into the fluid flow within the nozzle generating the observed spray plume changes. Overall, the comparison of LES and spray imaging data shows good predictive model capability with respect to jet breakup morphology, plume trajectory and plume angle.