Extinction mechanism of lean methanes/air turbulent premixed flame in a stagnation point flow

Effects of flame stretch, flame curvature and heat loss to the solid wall on the extinction of turbulent premixed flames formed in a stagnation point flow have been studied experimentally. Lean methane/air mixture, whose Lewis number is less than unity, was used. Bulk stretch rate was varied from 15 s^-1 to 60 s^-1, while the turbulent intensitys of velocity fluctuation in the approach flow was varied from laminar condition to 0.6 m/s. The flame stretch due to flow divergence was estimated by measuring the mean centerline velocity profile with LDV and the flame curvature and flame location were measured by using laser tomographic technique. The total stretch rate is defined as a sum of flame stretch due to flow divergence and that due to flame curvature. The lean methane/air flame is intensified by a Lewis number effect and the flame can locate close to the wall. As a result, the heat loss to the stagnation plate affects the flame and finally the flame is extinguished under the influences of both heat loss and the total flame stretch. On the other hand, the flame of premixed gas with Le>1 (e.g. lean propane/air flame) is extinguished due to total flame stretch. From these results, it can be concluded that the extinction mechanism of wrinkled laminar flame is supposed to be fundamentally the same as that of laminar flame when the flame stretch is reasonably estimated by taking into account the effect of flame curvature.