Ignition and extinction of homogeneous-heterogeneous combustion: CH4 and C3H8 oxidation on PT

The bifurcation behavior of homogeneous-heterogeneous combustion processes was studied experimentally and theoretically by examining surface and homogeneous ignition and extinction of methane and propane oxidation in air on platinum foil in stagnation flow at atmospheric pressure. A technique based on bifurcation theory and the shooting algorithm is used to simulate these experiments and gives remarkably good agreement with experiments using simplified rate expressions. Two ignitions, one extinction, and one self-sustaining autothermal steady state were observed for both systems. The first ignition is that of the heterogeneous reaction which is weakly dependent on the fuel composition over a large range of the composition. Autothermal behavior occurs over a large range of compositions for propane oxidation but only in a small region near the stoichiometric composition for methane oxidation. For all other compositions extinction occurred. Coking was observed for fuel rich mixtures in both systems. Comparison between theory and experiment demonstrates that bifurcation analysis can be used to predict experimental homogeneous and heterogeneous ignition/extinction using relatively simple models of the system. The model is also used to study the roles of the homogeneous and heterogenous reactions in these systems by calculating reaction rate, concentration and temperature profiles in the reacting boundary layer.