Combustion Instability Mode Transition in a Pilot Bluff-Body Stabilized Combustor

Abstract

The pilot flame’s effects on dynamic stability have been investigated in a pilot bluff-body stabilized combustor at atmospheric pressure. During the experiment, the pilot fuel proportion increased from 6 to 20% with an interval of 2%, while the total equivalence ratio remained unchanged. Simultaneous dynamic pressure and unsteady heat release rate measurement and analysis were used to identify and characterize combustion instability modes. Combustion dynamics were captured by a high-speed camera. High-speed images were further analyzed by using proper orthogonal decomposition. With the increase of pilot fuel proportion, the transition between combustion instability modes of 33 and 130 Hz was observed. Based on acoustic mode analysis, the 33 and 130 Hz modes corresponded to the first and second longitudinal acoustic mode, respectively. The results show that the pilot fuel proportion affects the local equivalence ratio distribution in the shear layer and the recirculation zone. As a result, it has significant effects on the dynamics of pilot and main flame interactions, which lead to different unsteady heat release characteristics. Finally, the phenomenon of mode transition occurs when different acoustic modes have been excited.