An Asymptotic and Numerical Investigation of Homogeneous Ignition

The gas-phase ignition of a fuel-lean premixed combustible gas is investigated in a forced convection two-dimensional laminar channel flow configuration established by two catalytically-active parallel plates placed at a distance 2b apart. The gaseous mixture has uniform inlet properties and both plate temperatures are constant and equal. First-order matched activation energy asymptotics are used to describe the reactive gaseous flow in conjunction with the boundary layer approximation, a one-step large activation energy gaseous reaction, and an infinitely fast (mass-transport-limited) catalytic reaction. A closed form ignition criterion is obtained for the gas-phase ignition distance in terms of nondimensional groups that are relevant to confined flows. The characteristic chemical and transverse diffusion time scales are included explicitly in the ignition criterion clearly demonstrating the competition between gaseous and catalytic fuel conversion while the effect of flow confinement (b) is included implicitly. The ignition criterion is valid over the range 0.002, x/(bRePr) , 0.16, with x the streamwise distance, Re the flow Reynolds number based on the channel halfwidth b and the uniform inlet properties, and Pr the Prandtl number. The temperature and transport parameter ranges of applicability are 1.5, TW/TIN, 3 (with TW/TIN the ratio of the catalytic wall to the inlet temperature) and 0.9, Le, 2.0 (with Le the Lewis number) respectively, rendering the ignition criterion of particular interest to hydrocarbon catalytically stabilized combustion (CST) applications. Numerical simulations are performed fo