Direct numerical simulation of near nozzle diesel jet evolution with full temporal-spatial turbulence inlet profile

Fuel atomization which begins with turbulence perturbation has a significant influence on engine performance. The effect of turbulence on near nozzle field characteristics under various liquid-gas density ratios is performed in present models. First, using three-dimensional DNS (3-D Direct Numerical Simulation) method, a time-varying single-phase fully developed turbulent pipe flow is generated to store time-varying outlet velocity databases which are then mapped as the two-phase jet inlet velocities. After that, the characteristics of near nozzle diesel jet evolution are studied by solving the two-phase turbulent flows and tracking the two-phase interfaces based on DNS and VOF (Volume of Fluid) methods. It shows that with fully developed turbulent inject velocities, the topology of the jet evolves gradually from violent wavy surface, ligaments, to droplet parcels with different dimensions and shapes, which are considered more realistic and different from uniform/sinusoidal perturbation inject velocities, especially in the near nozzle field. Jets surface distortion, stretched and sheared interface are captured. Three different separation processes in different downstream positions are detected. In the initial stage of the jet, long and narrow ligaments act as primary breakup. In the later stage, the whole breakup process evolves more disorderly and more intensively, so that flat and curly ligaments are observed. Also, higher gas densities and narrower nozzle sizes can accelerate the jet break-up process. Furthermore, the present work is reasonably compared with experimental and numerical modeling results. (C) 2017 Elsevier Ltd. All rights reserved.