Breakup mode of continuous-type liquid-liquid pintle injector

A pintle injector is necessary for the reuse of a launch vehicle. Significant studies have been conducted on the breakup process in impinging or swirl type injectors. However, the breakup process in liquid-liquid pintle injectors from injection to the atomization of liquid films has rarely been investigated. Therefore, in this study, the breakup mode and process quantified characteristics of the pintle injector were investigated. The backlight imaging technique was applied to capture the spontaneous phenomenon, and a longitudinal section view of the spray on the pintle injector was obtained using the 2P-SLIPI technique. The breakup modes were classified into three categories based on the spray shape (hollow cone, fishbone, and branch). The atomization process was investigated with high-speed and SLIPI images in chronological order. Schematics of the process were also prepared to understand the breakup mechanism. The dynamic characteristics, such as breakup frequency and peak amplitude, and static characteristic (breakup length) were investigated using the flow Weber number. Furthermore, the dynamic characteristics are dependent on the radial flow, and the static characteristics are influenced by the annular jet flow. This study will serve as a reference for the breakup mechanism and characteristics of a liquid-liquid pintle injector design.