Effect of hole-to-hole angle in the behaviors of shock cells and fuel redistribution under flash boiling conditions

The flash-boiling jets could produce shock cells in the near-nozzle region and cause shock-to-shock interactions, inducing collapse for multi-jet sprays. However, the effect of hole-to-hole angle (HHA) on the shock-to-shock interactions and the consequent fuel distribution has not been well understood. Herein, two twin-hole injectors with different HHAs were used to study the shock-to-shock interactions over a wide range of liquid temperature (Tliquid) and ambient pressure (Pamb). Both increasing Tliquid and decreasing Pamb could enlarge the individual shock cells, leading to the shock-to-shock interactions and the occurrence of inter-jet jets. Further analysis showed that the spray morphology was mainly determined by the structure of interacted shock cells comprised of primary and secondary cells. By utilizing the occurrence of inter-jet jets as the evidence of the occurrence of shock-to-shock interactions under the conditions where the shock cells cannot be optically observed, it was demonstrated that the shock-to-shock interactions can occur under engine-like conditions. A reduced HAA caused shock-to-shock interactions and the occurrence of inter-jet jets under relatively lower Tliquid and higher Pamb. It was also found that the reduction in HHA caused the significant change in the structure of interacted shock cells, and thus influenced the spray field and fuel distribution (i.e., spray collapse). Finally, the essentials of the limits of superheat level in correlating the flash-boiling spray behaviors were illustrated.