Influencing factors on thermoacoustic instability in combustion of arrayed micro-tubes

To elucidate the coupled effects of air preheat temperature, equivalence ratio, and Wobbe Index (WI) on thermoacoustic oscillation characteristics in micro-scale hydrogen combustion, systematic experiments were conducted using an arrayed micro-tube combustor. By adjusting WI, equivalence ratio (φ), and air preheat temperature, flame images and frequency spectra were acquired. Response surface methodology (RSM) was employed to construct a combustion instability map, enabling quantitative characterization of the influence of these three parameters on pressure oscillation amplitude. The results indicate that flames fueled by low- and medium-WI fuel exhibit periodic extinction–reignition processes, accompanied by a single dominant peak in the frequency spectrum and periodically distributed proper orthogonal decomposition (POD) modal energy, indicating typical thermoacoustic oscillations. The combustion oscillation intensity initially increases and then decreases with the equivalence ratio, peaking at φ ≈ 0.8. Flames with low WI (36.15 MJ m−3) are compact and exhibit high heat release intensity, triggering oscillations at φ = 0.8. Medium-WI fuel (48.3 MJ m−3) induce strong oscillations at φ ≥ 0.7, while high-WI fuel (60.44 MJ m−3) yields dispersed flames with reduced reactivity, weakening thermoacoustic coupling. Air preheating significantly suppresses acoustic feedback and broadens the stable operating range, with optimal stability achieved at 200 °C. The response surface analysis reveals significant nonlinear coupling among WI, equivalence ratio, and air preheat temperature, demonstrating their synergistic role in determining the stability boundaries of arrayed micro-tube combustion.