Abstract: To understand the stability characteristics of the kerosene swirl injector when gas injected into the feed-line in the pre-burner of staged combustion LOX/kerosene rocket engine, the stability characteristics of open-end swirl injectors with gas injection are investigated experimentally in the atmospheric environment. A gas injection apparatus is designed to inject air into the feed-line of injectors. The two-phase flow processes in the feed-line and the spray processes of the injectors are captured by a high-speed camera. The unsteadiness of the spray processes is evaluated by the image intensity analysis method. It is found that the processes and stability of sprays are significantly changed when the gas injected in the feed-line. The film breakup length and the spray angle decrease and the sprays become unsteady with the Klystron effect. The unsteadiness of the spray is large when the size of bubbles in the feed-line is large and the diameter of tangential orifices of the injectors is small. As the gas-to-liquid ratio increases, the dominant oscillating frequency reduces. The size of the bubbles and the two-phase flow pattern have a significant impact on sprays of swirl injectors different from that of common effervescent atomizers. The frequency of sprays oscillating is about 1-3 Hz when the annular flow pattern is exhibited, showing intermittent flow-stopping. The sprays oscillating and the Klystron effect may induce the periodical block of bubbles to tangential orifices.

Key words: open-end swirl injector, bubble, two-phase flow pattern, spray, stability, Klystron effect