Morphology analysis on the effect of injection pressure on jet trajectory deviation of multi-jet sprays

Abstract

Fuel spray behaviors play an important role in mixture formation, efficiency and emission of internal combustion engines. In this study, the effect of injection pressure on spray jet trajectory was investigated by using an asymmetric five-hole GDI injector. With schlieren imaging method, the ethanol spray development was captured under superheat degrees from 0.46 to 9.48, and the ambient pressure was fixed at 101.3 kPa. For the non-flash-boiling cases, the jet trajectory gradually deviated inward in the far field with the increase of injection pressure. For the flash boiling cases, the jet trajectory near the nozzle exit deviated outward under the relatively low injection pressures and deviated inwards with the increase of injection pressure. The outward deviation under relatively low injection pressure was attributed to the non-uniform vapor formation inside the nozzle orifice. The disappearance of near-field deviation under flash boiling conditions under high injection pressures could be attributed to the reduced time for nucleation and bubble growth inside the nozzle. Additionally, under both non-flash-boiling and flash-boiling conditions, the far-field deviation under high injection pressures could be attributed to the increased jet speed and the stronger jet-to-jet interaction. Compared with non-flash-boiling cases, the far field deviation under flash boiling conditions were more intense because of the enhanced atomization and it is believed that the smaller droplets were more inclined to move inwards. The remarkable effect of injection pressure on jet interaction of flash boiling sprays shows the potential of flexible jet targeting control at different engine loads.