Two-dimensional thermometry measurements in confined swirl flames using filtered Rayleigh scattering

Two-dimensional temperature measurements using filtered Rayleigh scattering (FRS) were performed in confined CH4/air swirl flames at atmospheric pressure. The investigated burner has a combustion chamber consisted of four quartz windows. The combustion chamber is 160 mm high with a square section of 50 x 50 mm(2). Measurements were challenging due to the strong interference from the incident laser impinging onto quartz windows, wall reflection and Mie scattering. Comparisons between the FRS and a conventional probe-based thermocouple were conducted through several investigated cases. Five operating conditions were studied with the equivalence ratios (phi) of the premixed CH4/air mixture covered a range of 0.67-0.83. Under each condition, five cross sections (C.S.) of the swirl flame were investigated and compared to analyze (1) the flame structures and temperature distributions of the instantaneous FRS images and (2) the uniform temperature radius as well as the joint probability density function (PDF) profiles of the averaged FRS signals. Results indicate that FRS can effectively suppress the background scattering and the average standard deviation of FRS measurements throughout the experiment is < 7.5%. The thermochemical state of the confined swirl flames is strongly influenced by phi, leading to varieties of flame structures and temperature distributions.