Lewis number effects on edge-flame propagation in lifted turbulent flames

Three turbulent lifted slot-jet flames of different fuel Lewis numbers are studied using direct numerical simulation (DNS). To reduce the computational cost, a one-step chemistry model is employed with a mixture-fraction dependent activation energy reproducing the dependence of the laminar flame speed on the equivalence ratio which is representative of hydrocarbon fuels. In addition to turbulent flames, axisymmetric laminar jet flames with a same chemistry model to that of turbulent flames are simulated. It is found that the maximum reaction rate decreases as the Lewis number increases in the laminar cases. Analysis of the turbulent cases reveals that the extinction limit is affected by the Lewis number of the fuel. The scalar dissipation rate of the extinction limit increases as the Lewis number decreases. For a given positive curvature, the conditional edge-flame propagation velocity on the curvature increases as the Lewis number decreases. This is similar to the observation in premixed flames and can be explained based on thermo-diffusive effects.