Effects of Liquid Film Instability on Spray Features of Liquid–Liquid Pintle Injectors

As one of the crucial structural parameters for the pintle injectors, the design of the skip distance ratio is still heavily empirical-dependent in engineering, and the intrinsic correlations between the skip distance ratio and spray characteristics of liquid–liquid pintle injectors are also unclear. Inspired by the observations that the instability of axial liquid film exerts significant influence on the downstream spray behaviors of a liquid–liquid pintle injector, the influence of the skip distance ratio on the instability of the axial liquid film and the subsequent spray characteristics of the pintle injector was experimentally investigated. The spray steadiness of the pintle injector was evaluated based on the instantaneous images using the proper orthogonal decomposition technique, and the effects of the skip distance ratio and the momentum ratio on the spray features were analyzed. Furthermore, a proactive strategy was proposed to adjust the liquid film instability by modifying the outer wall morphology of the pintle post, and the verification experiments were carried out based on three different wall morphologies. It was discovered that the rough wall enhances the axial liquid film instability and promotes the liquid sheet breakup and atomization of the pintle injector. These results provide new insights and valuable references for the optimization design of pintle injectors.