Dynamic Flow Characteristic of the Liquid Swirl Injector

Liquid rocket engines are divided into three parts: feed system, injector, and combustion chamber. Among them, the injector is a device for injecting the propellant which is supplied from the feed system into the combustion chamber. Depending on the performance of the injector, atomization and mixing characteristics of the propellant are enhanced, and that can be leading to stable combustion, and the efficiency of the overall rocket engine can be improved. A study on injector dynamics has been carried out as a method to reduce combustion instability, and Bazarov established the theory on it. An indicator of this combustion instability characteristic is the injector transfer function, which can be expressed as the propellant flow rate at the injector outlet to the pressure applied to the injector. In the case of swirl injector, peaks may occur at specific frequencies as the propellant passes through the injector. When this phenomenon occurs, the atomization characteristics of the outside of injector as well as the inside of the injector may be different due to the flow perturbation. In this study, a pulsator was installed on the injector feed line to apply a constant pressure perturbation to the working fluid. To investigate the flow characteristic change with the condition, a liquid film thickness measuring device designed by Lefebvre was installed in the injector body. From this device, the injector response characteristics were found as the shape of injector transfer function and image processing was performed to investigate the external atomization characteristics. Generally, there are two kinds of injectors, open type and closed type, for liquid swirl injector. In this study, we focused on closed type swirl injector, and investigated atomization characteristics changes with the excitation, and conducted further studies to found the causes of peak in the swirl injector.