Flame dynamics and oscillation characteristics based on statistical analysis in a combustor with prefilming and non-prefilming atomization

Suppressing thermoacoustic oscillations in low-emission combustors during their operation poses a major challenge. In this study, we report dynamic flame tests on combustors with prefilming (S1) and non-prefilming (S2) airblast atomizers. We used the image fast Fourier transform, proper orthogonal decomposition, dynamic mode decomposition, and continuous wavelet transform to obtain the spatial distribution of pulsations and spectral characteristics of the flames. The results reveal that the flames of S1 and S2 were significantly different. The combustor of S1 had a dome-attached flame confined to the primary combustion zone, while S2 had a lifted flame that filled the entire combustor. As the rate of airflow at the inlet increased, the flame of S1 exhibited oscillatory combustion, while the flame of S2 remained stable under all tested conditions, which was consistent with observations of its dynamic images. No characteristic peak was observed in the spectra of S2 under all operating conditions, and under rates of inlet airflow of 40 and 60 g/s for S1. However, pulsations in the chemiluminescence signals of the flame had a primary frequency of 116.4 Hz and secondary harmonic at 232.4 Hz at 80 g/s for S1. At 100 g/s, the S1 flame exhibited a primary frequency of 142.9 Hz, secondary harmonic at 285.4 Hz, and tertiary harmonic at 428.3 Hz. Minor adjustments to the geometry of the airblast atomizer can thus significantly alter the mode of spray-wall interactions and impact flame dynamics. Consequently, this study proposes a new control technique for instability suppression.