Effects of skip distance on the spray characteristics of a pintle injector

Abstract

Pintle injectors have several unique features that allow high-performance thrust control of rocket engines; thus, it can be used in reusable space launch vehicles. Because the orifice area is directly controlled in the thrust adjustment process, several geometric parameters of pintle injectors must be considered in the design and analysis. However, the influence of the critical parameters on the injector performance has not been extensively investigated. The research object in this study was the skip distance, as well as the throttling level, which is a key geometric parameter for pintle injectors. It is related to the travel distance of annular flow along the pintle surface. The operating range of the skip distance was 0.25–1.91 and the throttling level based on the mass flow rate was operated in the range of 20–100%. Water and air were used as simulants under atmospheric conditions. In these conditions, the spray angle and droplet size were experimentally obtained, and the gas velocity distribution near the pintle surface was numerically analyzed. In this manner, the gas velocity distribution was determined in terms of the skip distance and throttling level, and the corresponding effects on the spray characteristics were analyzed. In addition, the variation trends of the normalized spray angle and droplet size with the skip distance and throttling level were obtained. Finally, an appropriate skip distance was proposed from a design perspective, considering the standard deviation in each throttling level. The results can help elucidate the influence of the skip distance and the throttling level on the spray characteristics, thereby facilitating the design of pintle injectors.