Spray formation mechanism of diverging-tapered-hole GDI injector and its potentials for GDI engine applications

Abstract

The gasoline-direct-injection injector adopting the diverging-tapered-hole nozzle has appeared in the market recently, which has shown the improved spray atomization and lower engine particulate emissions compared to conventional straight-hole nozzles. However, the near-nozzle spray formation mechanism associated with this atomization potential of the diverging-tapered-hole nozzle has not been thoroughly clarified due to the difficulties in the near-field flow observation. The current study compares the in- and near-nozzle flow characteristics of the straight-hole and diverging-tapered-hole GDI nozzles using X-ray phase-contrast and absorption imaging techniques to unravel engaged mechanisms and discuss the potentials of the diverging-tapered-hole nozzle for GDI engine applications. The analyses focus on the in- and near-nozzle flow structure, and flow dynamics and stability outside the nozzle. The results showed that the diverging-tapered-hole nozzle coupled with proper hole length generated the radially expanding crescent-moon-like flow structure in the hole that promoted the spray atomization and dispersion outside the nozzle. The expansion of the hole cross-sectional area in the diverging-tapered-hole nozzle was appeared to attenuate the mutual interactions of fuel flows in the hole from various origins that formed rather stable sprays. These flow characteristics are discussed to be promising for the compact and robust spray generation for GDI engine applications.