Abstract – Thermo-difTusive ignition of porous solid fuel constituting a semi-infinite slab in contact with a hot oxidizing gas is analysed. Heat and oxidant are considered to be supplied to the fuel convectively in accordance with the instantaneous temperature and oxidant concentration differences between the fuel surface and the gas phase. Governing equations of the mass and energy have been analyzed by employing the Laplace transformation and the Laplace asymptotic method. Surface temperature-time histories have been obtained for the zeroth, first, and second order reactions based on the gaseous oxidant concentration. Effects of various governing parameters on ignition delay times have been discussed.