Effects of injection pressure on atomization and the mechanism of plume interference suppression in flash boiling sprays

Flash boiling spray is a promising atomization technique for producing finer droplets at relatively low fuel injection pressures (Pf), and has the potential to replace the widely adopted high-pressure injection technology in combustion systems. However, the extent to which flash boiling can serve as a substitute for high-pressure injection is still unclear. Furthermore, previous studies have reported that plume interference induced by flash boiling can be suppressed by increasing Pf, yet the underlying mechanisms remain to be elucidated. In this study, numerical simulations were integrated with advanced experimental techniques, including structured laser illumination planar imaging–laser-induced exciplex fluorescence/Mie scattering (SLIPI-LIEF/Mie) and particle image velocimetry (PIV), to quantitatively characterize both in-nozzle flow and external spray behaviors. Compared to a Pf of 14 MPa and fuel temperature (Tf) of 25 °C, a Pf of 0.5 MPa combined with a Tf of 101 °C not only produces similar droplet sizes, but also results in a more uniform droplet size distribution. Increasing Pf raises the fluid velocity, thereby reducing its residence time inside the nozzle and decreasing the difference between the fluid's saturated vapor pressure and its static pressure, which characterizes the degree of superheating. As a result, a lower vapor volume fraction (α) is observed at nozzle exit. Furthermore, higher Pf enhances fluid momentum, which provides greater resistance to vapor-induced disturbances. These two factors collectively suppress plume expansion and interference under elevated Pf conditions.