运用OH-PLIF方法探测预混火焰前锋结构

OBSERVING THE STRUCTURE OF PREMIXED FLAME FRONT BY OH-PLIF METHOD

运用OH-PLIF方法探测了不同燃料系数和出口湍流度下甲烷/空气的锥形预混火焰的火焰前锋结构.实验结果表明,网格湍流是火焰根部产生皱折和不稳定性的重要因素,并且这种不稳定性会沿着火焰面向下游发展;而在火焰下游尤其是火焰顶部,流场中的低频拟序结构是形成大尺度皱折以及破碎火焰面的直接原因.相比于富燃料工况,贫预混火焰的火焰前锋更容易产生不稳定性,产生大尺度的皱折.导致这种皱折的不稳定性只与燃料系数有关,完全依赖于火焰自身的动力学而与来流特征无关.

The flame front structures of the methane/air premixed flames are observed by using OHPLIF method in the different conditions of equivalence ratio and inlet turbulence intensity. The results show that grid turbulence is the important factor to cause the wrinkles and instability at the flame base, and the instability waves grow downstream along the flame surfaces. In the downstream position especially in flame tip, the large-scale wrinkles and discrete reaction zones in the flame fronts usually occur due to the coherent structures in flow. Contrasted to rich methane-air flame, the instability which can create large-scale wrinkles in flame fronts is easier to occur in a lean methane-air flame. This instability depends only on the equivalence ratio thus the flame dynamics and is no business of the characteristics of the inlet flow.