Extinction of turbulent premixed flames by small-scale turbulence at Kolmogorov microscale

By using the counterflow, premixed double flame stabilized in the forward stagnation region of the porous cylinder, we have accurately determined the extinction limits of laminar and turbulent propane-air premixed flames as a function of the equivalence ratio and the stretch rates. The flow-field and turbulence characteristics were measured along the stagnation streamline by a hot-wire anemometer for the case without combustion. The mean velocity profile is found to be independent of the turbulence characteristics and coincides with the theoretical one obtained assuming the potential flow. The turbulence intensity and Kolmogorov microscale are nearly constant along the stagnation streamline up to the proximity of the stagnation point. For the laminar flames, the critical velocity gradient at which the extinction occurs agrees well with the previous data obtained by different flame configurations. In the present study: the stretch rate induced by mixture turbulence is assumed to be the inverse of the Kolmogorov time scale, and the total stretch rate is estimated by the sum of the bulk stretch rate induced by the mean velocity gradient and the turbulence stretch rate. Results show that the total stretch rate at which the extinction of the turbulent premixed flame occurs coincides with the critical velocity gradient at which the laminar premixed flame extinction occurs. Therefore, the small-size eddies with the Kolmogorov microscale pig an important role in extinguishing the turbulent premixed flame. However, these eddies do not affect the combustion reaction at molecular scale.