Numerical study of premixed twin edge flames in a counterflow field

Characteristics of premixed edge flames established in a counterflow field with a stretch-rate gradient were numerically investigated by solving three-dimensional governing equations with detailed chemistry in the general curvilinear coordinates system. Local mole fractions of radicals, such as OH or CH, at the flame edge of a CH4/air mixture were found to be larger than those in other parts of the flame. On the other hand, local mole fractions of radicals in the flame edge of a C3H8/air mixture were smaller than those in other parts. These numerical results agreed well with the experimental results of the present authors. Moreover, it was elucidated that two flame edges of twin counterflow flames did not merge at the edge even in the case of the CH4/air mixture. The ratio of the local stretch rate at the flame edge to the extinction stretch rate for planar twin flames with the same equivalence ratio was 0.6 for the CH4/air mixture and 0.7 for the C3H8/air mixture. These numerical results also agreed with results of the past experiments. Moreover, as for relatively low stretch-rate gradients, the stretch-rate gradient had no strong influence on the characteristics of the edge flames.