Extinction Mechanism of Lean Premixed Flames in a Laminar Stagnation Point Flow

Effects of heat loss and flame stretch on the lean-limit extinction of laminar premixed flames in a stagnation point flow have been studied experimentally. The bulk stretch rate was varied from 40 s^-1 to 420 s^-1 while the Lewis number (Le) was varied from 0.85 to 1.8. The extinction of the lean propane/air flame (Le>1) is mainly caused by the flame stretch. On the other hand, the extinction of lean methane/air and lean methane/CCVC flames (Le<1) is caused not only by flame stretch but also by heat loss, since the flame is intensified by the Lewis number effect. Therefore, heat loss is predominant in the case of the lean methane/CO₂-O₂ flame whose Lewis number is smaller than that of the lean methane/air flame.