Mutual synchronization and flame dynamics in an axially fuel-staged lean-premixed combustion system

We experimentally study the acoustic coupling direction between two stages and the flame-acoustic interaction within and across stages in an axially fuel-staged lean-premixed combustion system. Using inter-system complex network analysis, we observe a tendency for the thermoacoustic amplitude to diminish when a preferential biased acoustic coupling direction from the secondary to the primary stage is established. We then use multivariable dynamic mode decomposition to examine the flame-acoustic interaction within and across stages. Our findings demonstrate that the secondary flame can play a pivotal role in driving thermoacoustic instability in the primary stage, and the thermoacoustic amplitude amplifies in the secondary stage due to a biased acoustic coupling direction from the primary stage to the secondary stage. This study highlights the potential of manipulating the operating conditions of the secondary stage to establish a biased acoustic coupling direction from the secondary to the primary stage. Such manipulation could be harnessed for designing passive control strategies for suppressing thermoacoustic oscillations. Additionally, this study addresses the importance of considering the secondary flame in stability assessments of the primary stage, recognizing its potential involvement in driving thermoacoustic instability within the primary stage.