Measurement of scalar dissipation in premixed flames

The dissipation rate of a scalar appears in the balance equations of many models of turbulent flows, reacting or otherwise. In this study, scalar dissipation in premixed flames is measured three-dimensionally using laser imaging techniques involving two closely spaced parallel beams and intensified CCD cameras. A progress variable, c, is derived from measured Rayleigh scattering intensities and computed results of a laminar flame code. In a lean turbulent premixed flame of Lewis number greater than unity, the conditional mean values of scalar dissipation, defined as N-zeta = [D del c .del c\c = zeta] (where D is diffusivity and zeta is a particular value of c), are found to be much less than the laminar flame values. Fine turbulence scales smaller than the laminar flame front thickness are thought to influence the mixing of radicals and have a broadening effect on the flame front.