Gas-phase and catalytic combustion in heat-recirculating burners

An experimental study of a spiral counterflow "Swiss roll" burner was conducted, with emphasis on the determination of extinction limits and comparison of results with and without bare-metal Pt catalyst. A wide range of Reynolds numbers (Re) were tested using propane-air mixtures. Both lean and rich extinction limits were extended with the catalyst, though rich limits were extended much further. With the catalyst, combustion could be sustained at Re ≥ 1.2 with peak temperatures ≥ 350 K. At low Re, the "lean" extinction limit was rich of stoichiometric, and rich-limit had equivalence ratios exceeded 40 in some cases. No corresponding behavior was observed without the catalyst. Gas chromatography indicated that at low Re, even in extremely rich mixtures, CO and non-propane hydrocarbons did not form. For higher Re, where both gas-phase and catalytic combustion could occur, catalytic limits were slightly broader but had much lower limit temperatures. Thus, combustion at low Re in heat-recirculating burners greatly benefit from catalytic combustion with the proper choice of mixtures that are different from those preferred for gas-phase combustion. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).