Characterization for premixed swirling methane/air diffusion flame through filtered Rayleigh scattering

The characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure have been measured by filtered Rayleigh scattering (FRS). Three operating conditions are investigated with the equivalence ratios (Φ) of the methane/air flame covered a range of 0.67-0.83. Under each condition, single-shot and averaged FRS images over a region measuring 39.3×65.6 mm2 at seven cross sections (S) of the flame have been collected to demonstrate the flame behaviors. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements. Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions (PDFs). The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The instantaneous FRS results display the momentary flame shapes and rolling vortices. The gradient of the instantaneous FRS images clearly illustrated the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behaviors of turbulent flames.