Effects of mixture composition and turbulence intensity on flame front structure and burning velocities of premixed turbulent hydrocarbon/air Bunsen flames

Abstract

The influences of the equivalence ratio, turbulence intensity, and different thermo-diffusive characteristics on the flame brush characteristics, instantaneous flame front structures, and burning velocities of premixed turbulent methane/–, ethane/–, and propane/air Bunsen flames were investigated systematically. Particle image velocimetry and Mie scattering techniques were utilized to measure the turbulence statistics and to visualize flame front corrugations, respectively. All experiments were performed under a constant bulk flow velocity of 21.0 m/s. The equivalence ratio range was from 0.7 to 1.35 for methane/air flames, 0.7–1.45 for ethane/air flames, and 0.8–1.35 for propane/air flames. Two perforated plates were used to produce different turbulence levels. A series of comprehensive parameters including the characteristic flame height, mean flame brush thickness, mean volume of the turbulent flame region, mean fuel consumption rate, two-dimensional flame front curvature, local flame front angle, two-dimensional flame surface density, wrinkled flame surface area, turbulent burning velocity, mean flamelet consumption velocity, and mean turbulent flame stretch factor were obtained. The mean turbulent flame stretch factor displayed a dependence on the equivalence ratio and turbulence intensity. Results show that the mean turbulent flame stretch factors for lean/stoichiometric and rich mixtures were not equal when the unstrained premixed laminar burning velocity, non-dimensional bulk flow velocity, non-dimensional turbulence intensity, and non-dimensional longitudinal integral length scale were kept constant.