Gas entrainment characteristics of diesel spray during end of injection transient

This paper reports the effect of injection parameters such as nozzle hole diameter and injection duration on gas entrainment of diesel sprays during the end of injection transient. The entrained gas flow fields of transient diesel sprays were measured using particle image velocimetry incorporated with the laser-induced fluorescence technique. To investigate the effect of injection parameters, two nozzles with different hole diameters and two injection modes (a quasi-steady injection with long injection duration and a transient injection with short injection duration) were applied. In all test cases, in order to compensate for the decreased mass inside the spray caused by the decrease in fuel supply, gas entrainment during the end of injection transient increased compared to that of the quasi-steady state. In the case of the nozzle with a larger hole diameter, the steeper decrease in fuel mass flow rate during the end of injection transient resulted in a higher rate of entrained gas flow compared to that of the nozzle with the smaller nozzle hole diameter. However, this increasing rate of gas flow rate appears similar regardless of applied injection modes, a quasi-steady injection with long injection duration and a transient injection with short injection duration, supposedly due to the similar decreasing rate of fuel mass flow during the end of injection transient. The decrease in mass inside the spray (mass disturbance) propagated from the nozzle tip region to downstream with time. This propagation speed of mass disturbance inside the spray was affected by the penetrating rate of the spray during injection, and increased through the nozzle with a larger hole diameter and quasi-steady injection with longer injection duration.