Experimental study on thermoacoustic coupled oscillating combustion mechanism of swirl diffusion flame based on phase analysis.

This article presents an experimental study on the thermoacoustic oscillation mechanisms in a single-stage swirling diffusion flame combustor, focusing on the dynamic interactions among velocity fluctuations, pressure fluctuations, and heat release rate fluctuations. A novel phase analysis model is developed to describe the closed-loop feedback coupling that governs self-excited oscillatory combustion, linking flame transfer function (FTF) characteristics with the acoustic response of the combustion system. The study systematically investigates how operating parameters—equivalence ratio, inlet Reynolds number, swirl number—and geometric parameters—combustion chamber length—affect oscillation frequency and intensity by altering phase delays and acoustic feedback. Key findings include that decreases in equivalence ratio and increases in Reynolds and swirl numbers reduce phase delay in heat release rate fluctuations, thereby increasing oscillation frequency and amplitude, while shorter combustion chambers shift oscillation modes to higher frequencies. These results provide insights for designing swirl combustors to predict and mitigate oscillatory combustion phenomena.