Temporal and spatiotemporal dynamics of the premixed bluff-body-stabilized flame under different combustor lengths.

This article experimentally investigates the temporal and spatiotemporal dynamics of a lean-premixed methane-air flame stabilized by a cylindrical bluff body, focusing on how varying the combustor length influences combustion modes. Under constant inlet conditions, increasing the combustor length transitions the system from stable combustion characterized by low-amplitude chaotic pressure oscillations and high-frequency flame dynamics in the shear layer, to thermoacoustic instability marked by high-amplitude, phase-synchronized periodic oscillations and low-frequency flame dynamics in the wake region, and finally to an intermittent combustion state exhibiting mixed features. The study employs dynamic acoustic pressure measurements, CH* chemiluminescence imaging, two-dimensional particle image velocimetry (2D-PIV), and advanced signal analyses (including cross-wavelet transform and proper orthogonal decomposition) to reveal that combustor length modulates the three-way coupling among combustion, acoustics, and hydrodynamics, thereby altering hydrodynamic stability and flame behavior. These findings provide experimental evidence that combustor acoustic feedback critically governs thermoacoustic combustion instability and its transitions, offering insights relevant to the design and control of combustion systems in propulsion and industrial applications.