Online cross-sectional monitoring of a swirling flame using TDLAS tomography

The purpose of this paper is to monitor the dynamic cross-sectional behavior of swirling flames using the tunable diode laser absorption spectroscopy (TDLAS) tomographic system. The newly developed online and highly spatially resolved imaging system based on TDLAS tomography was employed to monitor and reveal directly the reaction process in the swirling flame by reconstructing the 2-D distributions of temperature and H₂O concentration over a cross section of the flame. The system was demonstrated to be capable of capturing the temperature distribution accurately and inferring the thermal expansion over the cross section of interest in the swirling flame generated by a model swirl injector operating in partially premixed combustion mode. As the equivalence ratio was decreased, thermal oscillations extracted from the real-time 2-D reconstructions were used to infer the instability of the swirling flame. Furthermore, the developed system was applied to capture dynamically the process of blowout of the swirling flame, illustrating that the system can provide firsthand and reliable visual data to help prevent the flame from lean blowout (LBO). This paper reports the first experimental observation of the dynamic cross-sectional behavior of the swirling flame, enabled by the high spatial and temporal resolutions provided by the TDLAS tomographic imaging system. The developed system can help better understand the LBO mechanism so as to improve the performance of low-emission gas turbine combustors.