Diode Laser Absorption Tomography for Swirling Flame Diagnostics

The swirl burner plays an important role in the aero-engine combustor. Accurate diagnosis of the heat release rate distribution is helpful for studying thermos-acoustic instabilities, flame shape transition and turbulence-chemistry interactions in the swirl flames. Tunable diode laser absorption spectroscopy (TDLAS) is a powerful tool with which to probe atoms and molecules non-intrusively and has been used in combustion diagnostics. Combined with hyperspectroscopy tomography (HT), TDLAS can improve its spatial resolution. The diagnostics system was composed of 26 beams (13×13, 13 parallel beams and 13 vertical beams). Four water vapor absorption lines, 7 185.6, 7 444.3, 6 807.8, 7 466.3 cm^-1, were utilized in each beam using time-division-multiplexed method at total measuring frequency of 2.5 kHz. A reconstruction routine based on simulated-annealing algorithm was used to reconstruct the two-dimensional distribution of temperature and H₂O concentration. Comparisons with CFD simulations show that the reconstruction results reflect the real two-dimensional distribution of temperature in the swirl flame.