Flame front is a region in the flow field where rapid change in the chemical composition of the fluid occurs with consequent release of chemical energy in the form of heat. In the majority of cases the phenomenon is a very complicated one involving the heat transfer by conduction and radiation, the changes in concentration of the different components by diffusion and chemical reaction. Owing to this and the difficult problem of chemical kinetics, only recently the complete theory of flame front has been formulated, particularly by the group under J. O. Hirschfelder. Fortunately, as a result of the rapid rate of chemical reaction, the thickness of the flame front under ordinary conditions is generally very small, being less than 1 mm. Therefore, if one is interested in the influence of flame front on the flow field but not on the detailed structure of the flame, the flame can be assumed as infinitesimally thin, and only the final changes of the state of fluid due to combustion need be considered. This procedure is entirely analogous to that of treating the shock wave as having zero thickness in studying dynamics of compressible fluids. This simplification will be adopted for the present investigation.