Study on spray patterns of gas-centered swirl coaxial (GCSC) injectors in high pressure conditions

Recess ratio and momentum flux ratio are the key parameters in determining spray characteristics and mixing efficiency of the propellants in rocket injectors. In this study, effects of the recess ratio and momentum flux ratio on the spray patterns of gas-centered swirl coaxial (GCSC) injectors have been experimentally investigated through cold flow tests in a high pressure chamber, in which the liquid fuel and gaseous oxidizer are simulated by water and gaseous nitrogen, respectively. By elevating the chamber pressure, the cold flow test conditions are adjusted to match the ratios of momentum flux, density, and velocity between the gas and liquid flows to those of the actual hot-firing conditions. The results showed that the spray patterns change drastically from a wide hollow cone to a narrow solid cone as the gas to liquid momentum flux ratio increases. Also, the injector with the shorter recess needs a higher momentum flux ratio to have a similar spray pattern to that with the longer recess. Based on the measured spray contraction parameters, the critical momentum flux ratio, which determines the near-injector spray pattern as internal or external mixing, correlates with the recess ratio.