EFFECT OF NONUNITY LEWIS NUMBER AND FINITE-RATE CHEMISTRY ON THE DYNAMICS OF A HYDROGEN-AIR JET DIFFUSION FLAME

In jet diffusion flames, buoyancy-influenced torroidal vortices roll o utside the flame surface when the annulus air flow is low. The tempora l and spatial evolution of these vortices changes the stretch along th e flame surface, which results in a wrinkled laminar flame. A time-dep endent, axisymmetric mathematical model having a detailed chemical-kin etics mechanism is used to simulate the wrinkled flame surface of a lo w-speed H-2-air diffusion flame. The effects of Lewis number and finit e-rate chemistry on the steady-state and dynamic flame structures are examined. Results obtained with different models indicate that the siz e and shape of the outer structures are unaffected by the unity-Lewis- number and fast-chemistry assumptions. Experiments showed that the fla me temperature tends to increase when the flame is bulging and decreas e when it is squeezing. The lower Lewis number inside the flame-not th e change in the Damkohler number-was found to be responsible for the o bserved fluctuations in the flame temperature. Preferential mass diffu sion of different species causes an increase in water in the bulging r egions of the flame and an increase in radicals in the squeezing regio ns.