Experimental investigations on acoustic-velocity-flame dynamic characteristics of a stratified burner

To reveal the influence of interaction between pilot and main flames on flow and thermo-acoustic instability characteristics, high-frequency measurement devices such as high-frequency particle image velocimetry, high-speed camera, pressure sensors, and photomultiplier tube were applied to study the acoustic-velocity-flame dynamic characteristics of the stratified burner under ambient temperature and pressure. Results show that the pilot swirling flow significantly influences the acoustic-velocity-flame dynamic characteristics of the stratified burner. When the pilot and main stage are operated with a swirling air jet and swirling flame, the main recirculation zone disappears, the thermo-acoustic instability is strengthened and the frequency of thermo-acoustic instability is locked with the large-scale vortex shedding frequency. When the pilot stage is converted into a swirling flame, the main recirculation zone reappears downstream of the nozzle outlet, and the high temperature burned gas is rolled back to improve the combustion stability of the swirling flame. However, in this case, the interaction between the pilot and main flames makes the thermo-acoustic instability frequency not well consistent with large-scale vortex shedding frequency. The interaction between the main stage and pilot stage flames leads to the increase of the flame angle of the main stage. The heat release fluctuation at the flame interaction region is the most intense, and the large-scale vortex in the outer shear layer of the main stage also causes the flame to produce severe oscillation.