This article concerns the onset of linear instability in a simple model of
solid combustion in a semi-infinite two-dimensional strip of width l. The f
ree boundary problem that describes the model involves initial and boundary
conditions, including a nonlinear kinetic condition at the interface. The
linear problem governing perturbations to a basic solution is solved by the
method of images with the reaction front perturbation satisfying an integr
odifferential equation, This equation is then solved using Laplace transfor
ms. Finally, we perform a stability analysis for the model by studying the
solution of the reaction front perturbation. The inclusion of initial condi
tions enables us to show the development of linear instability from arbitra
ry initial small disturbances.