Propagation and extinction of stretched premixed flames

By using the symmetrical counterflow flame configuration and LDV mapping of the velocity profile, we have accurately determined for methane/air and propane/air mixtures their flame speeds as a function of the equivalence ratio and stretch, as well as the stretch rates and the associated flame speeds at the state of extinction. These data are expected to be quantitatively useful for the modeling of more complex flame and combustor phenomena. Results further show that for these mixtures the flame speed mostly increases linearly with increasing stretch, that the flame speed is finite at the state of extinction, and that the extinction limits for nearly adiabatic, stretchless, and planar flames appear to correspond to the flammability limits of the respective mixtures. Implications of the present results on the concept of flammability limits are also discussed.