Spray-induced air motion in single and twin ultra-high injection diesel sprays

Abstract

The air motion generated by the dispersion of single and twin diesel sprays at ultra-high injection pressures is analyzed using computational fluid dynamics (CFD) modeling. Injection pressures up to 300MPa are used to generate the sprays in air at ambient densities of 15 and 30kg/m3 at 298K. To validate the models, a single spray injected into an initially quiescent constant volume chamber is simulated using the Eulerian–Lagrangian approach. Reynolds–Averaged Navier–Stokes equations, with the k–ɛ turbulence model, are solved using an Eulerian formulation for the continuous phase. The discrete droplet phase is treated using a Lagrangian formulation together with spray sub-models. Results are validated with published experimental data. Macroscopic and microscopic characteristics of the single sprays are studied. The CFD results are combined with empirical formulations to evaluate entrainment into a single spray under different injection and ambient conditions. Gas flow field vortex structures are identified based on the swirling strength parameter. In addition, the effects of incidence angle and separation distance of dual interacting sprays on parameters such as tip penetration and Sauter mean diameter (SMD) are investigated. In the case of twin sprays, to evaluate the expansion of the merged spray, a cone angle is defined and compared for different injection point separation distances and incidence angles. Finally, the spray-induced air motion characteristics of the twin sprays are discussed in terms of the vortical structures identified in the gas field.