Accurate Measurements and Analysis of the Thermal Structure of Turbulent Methane/Air Premixed Flame

This paper provides further experimental and numerical results concerning the premix turbulent combustion of lean methane-air mixture. For V-shaped flame, the experimental data were acquired by two-dimensional Rayleigh scattering technique. The main purpose of this investigation is to obtain quantitative information on the instantaneous thermal structure of the flame front for both laminar and turbulent conditions. Four values for turbulence intensity have been considered. The flame surface density is closely related to the two-dimensional temperature gradient. For turbulent combustion, a general decreasing trend of averaged temperature gradient was observed. However, this tendency is inverted for very high turbulence intensity when the instantaneous temperature gradient presents high fluctuations. The flame front thickness PDF and the curvature PDF decrease with the turbulence intensity. The joint PDF of curvature and the maximum of the progress variable's gradient have the tendency to rotate counterclockwise with the increase of turbulence intensity. Negative curvature brings more energy in preheat zone of flame and enhances combustion; consequently the temperature gradients increase.