Effects of Grooved Pintle Tip Applied to a Gas–Liquid Pintle Injector

Pintle injector is well-known for its high performance in overall thrust level of throttling. This feature is attributed to its ability to control propellant injection area, in which one propellant is injected radially and the other propellant is injected to annular direction. However, despite to this capability to regulate injection area, the momentum of radial flow in low throttling level is usually not sufficient to obtain appropriate spray characteristics, which include spray angle and droplet size. As a solution of this problem, a grooved pintle tip is proposed in this work. This grooved tip has several grooves on the upper side of pintle tip where radial flow is formed, and it blocks the injection area at different ratio depending on the throttling level. Cold flow tests using normal and grooved pintle tip with changing mass flow rate and annular orifice area were conducted, and the spray characteristics of pintle injector with these two types of pintle tips were compared. When grooved pintle tip was applied, spray angle of pintle injector was larger than that of the normal pintle tip case. Also, the droplet size was smaller than when a normal pintle tip was used. Therefore, the grooved pintle tip may contribute to preventing spray characteristics of pintle injector from deteriorating combustion characteristics in low throttling level, while maintaining the spray characteristics as in the case of normal pintle tip at middle and high throttling levels.