Premixed turbulent flame front structureinvestigation by Rayleigh scattering in the thinreaction zone regime

摘要

Premixed turbulent flames of methane–air and propane–air stabilized on a bunsen type burner werestudied using planar Rayleigh scattering and particle image velocimetry. The fuel–air equivalence ratiorange was from lean 0.6 to stoichiometric for methane flames, and from 0.7 to stoichiometric for propaneflames. The non-dimensional turbulence rms velocity, u'/SL, covered a range from 3 to 24, correspondingto conditions of corrugated flamelets and thin reaction zones regimes. Flame front thickness increasedslightly with increasing non-dimensional turbulence rms velocity in both methane and propane flames,although the flame thickening was more prominent in propane flames. The probability density functionof curvature showed a Gaussian-like distribution at all turbulence intensities in both methane and propaneflames, at all sections of the flame.The value of the term Dk, the product of molecular diffusivity evaluated at reaction zone conditions andthe flame front curvature, has been shown to be smaller than the magnitude of the laminar burning velocity.This finding questions the validity of extending the level set formulation, developed for corrugatedflames region, into the thin reaction zone regime by increasing the local flame propagation by addingthe term Dk to laminar burning velocity.