THERMAL IGNITION ANALYSIS IN BOUNDARY LAYER FLOWS.

The weakly reactive state leading to the ignition of a steady laminar boundary layer flow of a combustible mixture over a hot, isothermal, non-permeable, non-catalytic flat plate is studied both numerically and also using matched asymptotic analysis in the realistic limit of large activation energy. It is shown that the flow consists of a locally similar diffusive-reactive region next to the plate and a non-similar diffusive-convective region external to it; that the analytic solution obtained reproduces the lower half of the S-shaped ignition-extinction response curve such that ignition is expected to occur when a suitably-defined Damkoehler number, which increases with the streamwise distance, reaches unity; and that at the point of ignition, the heat transfer from the wall vanishes identically. An explicit expression for the minimum distance for ignition to occur has also been derived.