Investigation of 10 kHz Filtered Rayleigh Scattering and CH₂O Planar Laser-Induced Fluorescence Measurement in Two-Stage Swirl Combustor^†

We present an exploration of two-dimensional flame thermometry and CH₂O field measurement in a swirling flame within a two-stage radial stratified swirl combustor, operating under atmospheric pressure conditions. The research details the calibration and analysis of filtered Rayleigh scattering (FRS) signal intensity, employing a planar flame from a Hencken burner to establish a calibration curve for the FRS signal ratio and temperature. The 2-D temperature field results for the swirling flame are then showcased, all obtained using the calibrated FRS system. Parametric analysis focuses on the temperature fields of methane/air mixtures with equivalence ratios ranging from 0.65 to 1.05. The flame shape changes from V-shape to M-shape for a single-swirling flame with an equivalence ratio of 0.85, and that this change in shape is due to a combination of thermal diffusion effects and air-conducting effects. Furthermore, in the dual-swirling flame, the study identifies a transition from mergence to stratification during combustion in both the pilot and main stage flames under the same operating conditions. The article concludes by presenting and comparing the phase-averaged temperature field distributions and instantaneous CH₂O distributions during the stratified phenomena of the dual-swirling flame.