Experimental study on the macroscopic characteristics of air-assisted diesel spray

This study aims to examine the effects of ambient pressure and injection parameters on the macro-characteristics of air-assisted diesel spray. To illustrate the morphological variation of spray and the formation of vortex ring, the spray diffusion angle was defined. The results indicate that high ambient pressure hinders the radial and axial development of spray and delays the formation of vortex ring. As the ambient pressure increased from 1 bar to 2 bar, the formation of vortex ring was delayed by approximately 0.5 ms. Extending fuel injection duration reduced the spray penetration and increased the far- and near-field spray angles; however, the spray diffusion angle decreased. Increasing fuel injection pressure produces more small-sized droplets owing to enhanced droplet breakup, which decreased the spray penetration and facilitated the lateral diffusion of droplets. Increasing mixture injection duration did not affect the spray penetration; however, the variation of the diffusion angle was slowed down after the mixture injection ended. The insufficient fuel-air interval cannot adequately decelerate the injected fuel droplets, resulting in large penetration and weak lateral diffusion. And there was a critical interval between 1.0 ms - 3.0 ms in this study, after which the fuel droplets could be decelerated sufficiently.