Dynamic Characteristics of Open-Type Swirl Injector with Varying Geometry

Abstract

Combustion instabilities in a liquid rocket engine are generated by coupling between the heat release oscillations and the acoustic pressure oscillations in the combustion chamber. These instabilities from the combustion chamber can affect the injector and the feed line, which are in front of the combustion chamber. These oscillation transfers could influence the combustion instability in liquid rocket engines. A properly designed injector can be used to prevent these transfers and suppress combustion instability. For this reason, the dynamic characteristics of the injectors must be studied. Open-type swirl injectors were designed to investigate the dynamic characteristics through experimental study. The injectors were designed with replaceable parts to change the swirl chamber length, swirl chamber diameter, tangential entry number, and manifold diameter. A hydrodynamic mechanical pulsator that produces pressure oscillations in the feed line was installed in front of the manifold of the open-type swirl injector. The pressure in the manifold, the liquid film thickness, and the pressure at the exit of the open-type swirl injector were measured to understand the dynamic characteristics of the open-type swirl injector. As a result, the open-type swirl injector’s response characteristics to pressure fluctuation inputs with different geometries were obtained. The tendencies of the output parameters acquired in the study could be used to adjust the injector design to suppress combustion instability in liquid rocket engines.