Effects of annulus width and post thickness on self-pulsation characteristics for Liquid-Centered Swirl Coaxial Injectors

Abstract

Based on the experimental and numerical methods, parametric studies on annulus width and post thickness of a liquid-centered swirl coaxial (LCSC) Injector were performed under atmospheric conditions to evaluate their effects on the internal flow dynamics, self-pulsation characteristics and atomization qualities. Filtered water and dried air were employed as simulant mediums. 2-D unsteady numerical simulations based on the swirl axi-symmetric model were conducted. The instantaneous self-pulsated spray images were captured with a back-lighting photography technique. By means of the Dantec Phase Doppler Anemometry (PDA) system, the atomization qualities including Sauter mean diameter (SMD), velocity of droplets and mass flow rate have been characterized. Results showed that annulus width and post thickness of inner injector together with the recess length have significant influences on self-pulsation. Violent liquid sheet pulsations are caused by the tremendous dynamic pressures imposed from the blocked annular gas stream. Whether self-pulsation occurs or not and self-pulsation intensity essentially depend on the relative magnitude of liquid film angle and recess angle. Increasing the annulus width and post thickness leads to an accompanying decay in self-pulsation. Furthermore, it was found that the mass flow rate distribution of self-pulsated spray is double-peaked while that of stable spray is single-peaked. SMD and velocity distributions of all droplets are more susceptible to the injection conditions rather than the geometrical parameters.