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.