Gas-phase and catalytic combustion in heat-recirculating burners

An experimental study of a spiral counterflow "Swiss roll" burner was conducted, emphasizing on determination of extinction limits and comparison of results with and without bare-metal Pt catalyst. A wide range of Reynolds numbers (Re) was tested using propane-air mixtures. With catalyst, combustion could be sustained at Re ≥ 1.2 with peak temperatures ≥ 350 K. A heat transfer parameter characterizing the thermal performance of both gas-phase and catalytic combustion at all Re was identified. At low Re, the lean extinction limit was actually rich of stoichiometric and rich-limit had equivalence ratios exceeded 40 in some cases. No corresponding behavior was observed without catalyst. Gas-phase combustion generally occurred in a flameless mode near the burner center. 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. At sufficiently high Re, catalytic and gas-phase limits merged. Thus, combustion at low Re in heat-recirculating burners benefited greatly from catalytic combustion with the proper choice of mixtures that are different from those preferred for gas-phase combustion.