An experimental study of the effects of platinum on methane/air and propane/air mixtures in a stagnation point flow reactor

A stagnation-flow burner facility was used to study the catalytic surface reactions of premixed combustion systems at atmospheric pressure. The configuration serves as an important platform to investigate the interaction between homogeneous and heterogeneous reactions with independent control of the characteristic chemical and physical residence time scales. Methane/oxygen/nitrogen and propane/oxygen/nitrogen mixtures were examined with and without the presence of a platinum catalyst located at the stagnation surface. The effects of oxidizer composition and nitrogen dilution were investigated. Lean flame extinction limits were determined for the two fuels and were found to be unaffected by the presence of the catalytic surface. The flame extinction data indicated that the systems were controlled by gas phase combustion with negligible contributions from heterogeneous reactions. The catalytic activity of the heated surface in response to the direct impingement of fuel/air mixtures onto the stagnation surface, without the presence of a flame, was quantified by the increase in the surface temperature. The methane/air mixtures demonstrated no catalytic activity for these conditions, whereas propane/air mixtures demonstrated temperature increases of over 100 K. The data indicate that the surface reaction was transport limited for the propane/air system.