Effect of Lewis number on flame propagation through vortical flows

The premixed gas flame spreading through an array of large-scale vortices is studied numerically. It is found that the flame speed is a nonmonotonic function of the stirring intensity. At sufficiently low Lewis numbers (Le(less than)1) the system becomes bistable with a hysteretic transition between possible propagation modes. In the presence of volumetric heat losses the stirring invariably promotes extinction (reduces the flammability limits), provided Le(greater than)1. At Le(less than)1 this holds only for sufficiently strong stirring, whereas moderate stirring actually expands the flammability limits. At Le(greater than)1 the deficient reactant is fully consumed up to the very quenching point. At Le(less than)1, prior to the total extinction, part of the deficient reactant escapes the reaction zone and remains unconsumed.