Effect of Rectangular Orifice Structure on Spray Oscillation of Liquid–Liquid Pintle Injector

The impingement between the liquid jet and the liquid film induces the spray oscillation of the liquid–liquid pintle injector, which is crucial for understanding the breakup processes and mechanisms. However, the effect of the rectangular orifice structure on oscillation characteristics remains unclear, and the orifice structure has a close linkage with the blocking factor, which is a key structural parameter for pintle injectors. The present study processed and analyzed the spray images of varying height-to-width ratios (HWRs). The breakup and atomization processes of the liquid jet impinging on the liquid film were not directly influenced by changing HWR, and the effect of HWR on the spray angle was limited. Alternatively, the oscillation characteristic parameters presented observable variations at different HWRs. When decreasing the HWR, both the maximum amplitude and the oscillation frequency decreased, but the location of the maximum amplitude, breakup length, and oscillation wavelength increased. At low HWR, the jet carried more liquid film, hindering the breakup and causing an increase in breakup length and wavelength. Meanwhile, part of the oscillation energy was dissipated along the spanwise direction, leading to a smaller amplitude. Furthermore, the fitting empirical equations of the breakup length and wavelength were derived from the experimental results.