Gas-phase ignition of accelerated boundary-layer flows on strongly catalytic surfaces

Abstract

Ignition of a combustible, wedge-type boundary-layer flow on a strongly catalytic surface at a high temperature is treated theoretically. Because of the heat release of the surface reaction, this constant surface temperature is maintained by either external cooling or an adiabatic wall. An explicit criterion of ignition defined as the critical Damköhler number in the gas phase, which depends primarily on the Prandtl number, the Schmidt number, the wedge angle and the surface temperature, is derived in the limit of large activation energy. The regions of ignition and of absence of ignition are identified. The results show that the growth of the region where ignition occurs is achieved by either decreasing the wedge angle or increasing the surface temperature and the Prandtl number. The ignition region for an adiabatic wall is greater than that for external cooling. For an adiabatic wall, the ignition region decreases monotonically as the Schmidt number increases. For external cooling, an optimal Schmidt number exists for which the ignition region is greatest.