Single-Hole Asymmetric GDI Injector: Influence of the Drill Angle and the Counter-Bore under Flash-Boiling and Non-Flash-Boiling Conditions

Sac-type nozzles, which are often used in gasoline direct injection (DI), induce asymmetry to the spray. The drill angle, that is, the angle between the axis of the nozzle and the axis of the injector, is one of the key causes of the asymmetric flow. Despite its significance, the influence of the drill angle on spray is poorly understood. In the current work, a parametric study has been carried out using single-hole sac-type nozzles by varying the drill angle. The drill angle was varied from a value of 0° to 45° in steps of 15°. Apart from the geometric variation, the ambient pressure and the fuel temperature were varied to achieve flash-boiling and non-flash-boiling spray conditions. Simulations were carried out using an in-house computational fluid dynamics (CFD) solver that accounts for thermodynamic non-equilibrium coupled with a liquid-gas interface-area-density transport model to account for primary atomization of the fuel. The spray angle was calculated on the basis of a threshold analysis applied to the liquid-gas interface-area-density. The results indicate that the drill angle has a significant influence on the near-nozzle spray, where larger drill angles cause wider sprays.

An analogy between a stepped-hole nozzle and a convergent-divergent nozzle was speculated in recent experimental and computational studies. Therefore, to further the understanding of this proposed analogy, the current study also explored the influence of the counter-bore on the ensuing spray. An analysis of the pressure field and the static pressure drop along the axis of the nozzle shows that the counter-bore acts like an expansion chamber, thereby causing flash-boiling sprays to behave like underexpanded supersonic jets and non-flash-boiling sprays to behave like overexpanded jets. However, a further investigation of this hypothesis is necessary before its potential use as a design tool.