Effects of Recess on the Self-Pulsation Characteristics of Liquid-Centered Swirl Coaxial Injectors

Abstract

The self-pulsation characteristics of liquid-centered swirl coaxial injectors have been investigated using a Photron Fastcam SA-1.1 camera and a PULSE system (B&K Corp., 3650 type). The effects of both recess length and injection condition were analyzed and discussed. The flow pattern in the recess chamber of a liquid-centered swirl coaxial injector can be classified into three types, namely, outer, critical, and inner mixing flow. Once the critical flow approaches, self-pulsation is about to occur. When self-pulsation occurs, the spray oscillates with a Christmas tree shape. The Christmas-tree-like spray periodically produces droplet clusters, making horizontal spray width and mass flux oscillate periodically. Self-pulsation is the strongest when the flow is around the critical mixing flow. Both variations of recess length and injection condition can change the flow pattern in the recess chamber. When the flow pattern moves away from the critical mixing flow, self-pulsation is suppressed. All the frequency behaviors of self-pulsation indicate that self-pulsation is strongly related to Kelvin–Helmholtz instability. A possible mechanism of self-pulsation is also presented. This mechanism interprets the experiments of the present study and the results of literature well.