Stabilizing Mechanism of Edge Flame in an Axisymmetric Wall Jet

Stabilizing mechanism of a methane-air edge flame that is a partially premixed flame, is investigated experimentally using the axisymmetric wall jet burner. Measurements of stability limits, flame locations and velocity fields with PIV, and visualization of themal boundary layer around of the edge flame have been performed. As a result, it is found that Peclet number Pe, which is expressed as Pe= Ut× pe/D, where Ut is tangential velocity toward the edge flame, Pe is curvature radius of thermal boundary layer of the edge flame and D is mass diffusivity, shows constant value at stability limits. The Pe physically means the ratio between partially premixing time to form flammable mixing layer and residential time of a fluid element in partially premixing region. Therefore, the result obviously indicates that the edge flame's stability is determined due to the balance between the partially premixing time and the residential time in partially premixed region. Thus, it is clear that a partially premixing, which is absent in a pure premixed flame, is important for stabilizing mechanism of the edge flame in the wall jet.