Droplet Size Control in Gas-Liquid Pintle Injectors

Due to their suitable characteristics for throttleable rocket engines, interest in pintle injectors has been recently re-newed. Many studies have focused on the correlation between spraying conditions and spray or combustion characteristics for pintle injector. However, there is no previous study on the correlation between spray and combustion characteristics due to the di ffi culties in controlling each spray characteristic individually. This research presents a solution to this problem. For the control group, a 400 N gas-liquid pintle injector for liquid oxygen and gas methane is designed and its spray characteristics are measured through cold- fl ow tests. In sequence, a ‘ reverse injection ’ idea and its design are proposed to increase spray angle while maintaining the droplet size, which is represented by the Sauter mean diameter. In addition, in the design proposed, the reverse injection e ff ect is intensi fi ed as the throttling level increases, decreasing the di ff erence of spray angle between throttling levels. In a cold- fl ow test, air and water were used under an atmospheric condition for gas-liquid fl ow simulant. The spray angle and droplet size were measured using the shadow method. The ‘ reverse injection ’ feature proposed functioned properly, increasing the spray angle of the injector while maintaining the droplet size.