Dynamic Characteristic Analysis of a Gas–Liquid Swirl Injector Using Planar Laser Imaging

Abstract

The oscillation of the mass flow rate of the input propellant in liquid rocket engines may induce a periodic heat energy release within the combustion chamber, resulting in operational instability. Since propellant components are discharged from the injector head, the injectors can play a role as a source of oscillation in the dynamic system of a liquid rocket engine. Prior studies confirmed that if the liquid spray and gas flow intersect by using gas-centered dual-swirl injector with tangential inlet in the gas flow path, droplets are generated with periodicity (fracture frequency). In this study, the characteristics and mechanisms of this periodicity were analyzed using longitudinal cross-section spray images. Since the multiple scattering signal that inhibits clarity is non-modulated components, it can be removed by using two modulated images with a phase difference of 180 deg (two-phase structured laser illumination planar imaging technique). And the dynamic characteristics of the gas–liquid spray were analyzed by applying the fast Fourier transform method. It was confirmed by this method that the fracture frequency was related to the impinging velocity of gas and hydrodynamic feature of liquid film. That is, it can be said that fracture frequency of the liquid film is dependent on the liquid Weber number and gas Weber number as the entrainment effect and impact force by gas flow are applied to the liquid film.