Numerical study on the effects of eccentric nozzles on spray evolution using a hybrid method

Abstract

In this paper, a methodology is proposed to couple between the nozzle inner flow and external spray and atomization. A hybrid VOF-DPM model is developed to investigate the influence of different eccentricities (0, 0.5, 0.62, and 0.81) on the atomization characteristics of diesel engine nozzles. Large eddy simulations (LES) are performed to capture the nozzle inner flow and morphology of the breakup. The atomization performance is evaluated in terms of spray morphology, spray cone angle, penetration distance, and droplet size under high-pressure injection and non-evaporative conditions. The model is validated using the "Spray C" nozzle from the Engine Combustion Network (ECN), with simulation results showing good agreement with experimental findings. The research reveals that elliptical nozzles generally outperform circular ones in terms of discharge performance and atomization quality. The appropriate increase in eccentricity enhances atomization by promoting liquid breakup and reducing penetration distance. The primary breakup is strongly influenced by the turbulence shear stress inside the nozzle and the aerodynamic forces in the near field. Thus, the promoting atomization mechanism of the eccentric nozzle is that the eccentric structure intensifies pressure fluctuations and turbulent disturbances, thereby exacerbating the fracture of the liquid core and the stretching and breaking of the tip thin sheets during the primary breakup, peeling off more entrained droplets. The smaller and more uniformly distributed tiny droplets are then generated through secondary atomization.