GDi Skew-Angled Nozzle Flow and Near-Field Spray Analysis using Optical and X-Ray Imaging and VOF-LES Computational Fluid Dynamics 2013-01-0255

Improvement of spray atomization and penetration characteristics of the gasoline direct-injection (GDi ) multi-hole injector is a critical component of the GDi combustion developments, especially in the context of engine down-sizing and turbo-charging trend that is adopted in order to achieve the European target CO₂, US CAFE, and concomitant stringent emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to improve the GDi multi-hole spray characteristics.

This publication reports VOF-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 skew angle on the nozzle flow and spray primary breakup. VOF-LES simulations of a single nozzle-hole of a purpose-designed GDi multi-hole seat geometry, with three identical nozzle-holes per 120° seat segment, are performed. The simulations are complemented by comparison with the spray near-field breakup structure obtained through optical shadowgraphy and phase-contrast x-ray imaging techniques.

The spray shadographic and X-ray imaging data reveal the jet primary breakup in the immediate vicinity of the nozzle, representative of the "atomization regime." The jet morphology indicates the effect of injector valve-group hydraulic pressure oscillations. The VOF-LES simulations show fully-attached nozzle flow, and an "atomization regime" spray primary breakup in close agreement with the spray imaging data. The simulations highlight the effect of nozzle counter-bore on the jet primary atomization, through influence on the jet interface instability and, more notable, the physical interaction with the atomizing spray plume. Overall, the comparison of VOF-LES simulations with the spray imaging data shows good predictive capability with respect to the jet primary breakup, the plume macroscale features (trajectory, cone angle) and the observed effect of nozzle geometry.