Extinction of lean propane/air turbulent premixed flames in a stagnation point flow

Effects of flame stretch and flame curvature on the extinction of turbulent premixed flames in a stagnation point flow have been studied experimentally. A lean propane/air mixture was used. Bulk stretch rate was varied from 15 s^-1 to 60 s^-1, while the turbulence intensity of velocity fluctuation in the approach flow was varied up to 0.6 m/s. Near the extinction limits, the local stretch rate was estimated by measuring the mean centerline velocity with LDV and the local flame curvature was measured using a laser tomographic method. The local stretch rate due to flow divergence decreases, while the stretch rate due to the local flame curvature increases with increase in the turbulence intensity. As a result, it is proposed that the sum of those two stretch rates plays a key role in flame extinction.