Stability of Diffusion Flame formed in a Laminar Flat Plate Boundary Layer : Effect of Fuel Dilution

A stability limit of the diffusion flame with fuel injection from a porous wall in a laminar flat plate boundary layer is measured as functions of fuel (CH4) concentration of CH4/N2 injectant mixture (x) and its injection velocity (v). The free stream velocity (U∞) is set as 0.6 m/s. The thermal condition at the wall is controlled by setting temperature at the upstream end of the porous wall as a reference temperature. When v>20 mm/s, the flame becomes unstable with the separation of leading flame edge with decreasing x. The value of x at the stability limit is constant without regard to v as long as the wall temperatrure is kept constant. As the wall temperature is decreased the value of x increases. The separation is supposed to take place as a result of the limit of the reaction rate. When v