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It has been observed that intermittent injection leads to improved spray characteristics in terms of mixing and gas entrainment. Although some experimental work has been carried out in the past, the disintegration mechanisms that govern the breakup of intermittent jets remain unknown. In this paper we have carried out a systematic numerical analysis of the breakup of pulsated jets under different injection conditions. More specifically, the duty cycle (share of active injection during one cycle) is varied, while the total cycle time is kept constant. The advection of the liquid phase is handled through the Volume of Fluid approach and, in order to provide an accurate, yet computationally acceptable, resolution of the turbulent structures, the implicit Large Eddy Simulation has been adopted. The results show that the primary disintegration results from a combination of stretching, collision and aerodynamic interaction effects.

In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio. In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction.