Spray angle prediction model for a multi-slit type throttleable gas–liquid pintle injector

As a representative type of variable-area injectors, pintle injectors have been applied to various throttleable rocket engines. Spray angle is one important parameter among various spray characteristics of pintle injectors. Several prediction models for the spray angle of pintle injectors of various configurations have been investigated; however, the spray angle model for multi-slit type throttleable pintle injectors with adjustable radial flow injection area has not been sufficiently addressed. Therefore, in this study, a spray angle prediction model for a multi-slit type throttleable gas–liquid pintle injector that considers radial flow deflection and axial flow decay is proposed. With the axial flow velocities validated via numerical analysis, the radial flow angle and spray angle models are validated through cold flow experiments with a wide range of momentum ratios and throttling levels in the range of 20–100 %. The newly proposed spray angle model agreed well with the experimental results, indicating that the geometric parameters should be applied separately according to the radial flow opening, which depends on the throttling level when predicting the spray angle.