Laminar boundary layer flow of a combustible gas over a semi-infinite porous surface

Abstract

Laminar boundary layer flow of a combustible gas under mixed convection over a semi-infinite porous surface is analyzed theoretically and numerically. The governing equations are transformed into a set of partial differential equations which are solved numerically by using finite difference method. To assess the accuracy of numerical results, we also solve these equations by using perturbation method for low frequency range and asymptotic method for high frequency range. Numerical computations have been carried out for several values of parameters involved in the equations, namely the Prandtl number, the Schmidt number, the wall temperature and the mass flux for injected fuel. Results show that the momentum, thermal and concentration boundary layers increase owing to the increase in the mass flux, but increasing Prandtl number reduces the thermal boundary layer and thickens the momentum and concentration boundary layers. Moreover, an expression for the ignition distance involving the pertinent parameters is derived using large activation energy asymptotics. It is found that the ignition distance considerably diminishes upon increasing the above parameters.