The results from the observed combustion behavior of propane over platinum and rhodium catalysts in a meso-scale heat recirculating combustor are presented. The extinction limits, conversion, product selectivity/yield, and activation energy using the two catalysts were compared in an effort to determine their performance using a liquid fuel. The extinction limits were also compared to those of non-catalytic combustion in the same reactor. The results showed that the addition of a catalyst greatly expanded the range of stable operating conditions, in respect to both extinction limits and flow rates supported. The Rh catalyst was found to exhibit a higher propane conversion rate, reaching a maximum of 90.4% at stoichiometric conditions (as opposed to the 61.4% offered by the Pt catalyst at lean conditions); however, the Pt catalyst had superior CO2 selectivity for most studied conditions, indicating higher combustion efficiency. The Pt catalyst also had a significantly smaller activation energy (13.8 kJ/mol) than the Rh catalyst (74.7 kJ/mol), except at equivalence ratios richer than Φ = 1.75 (corresponding to catalyst temperatures below 500 °C), where it abruptly changed to 211.4 kJ/mol, signifying a transition from diffusion-limited reactions to kinetically limited reactions at this point. The results reveal that Rh would be a more suitable catalyst for use in a liquid-fueled meso-scale combustor, as fuel conversion has been shown to be a limiting factor for combustion stability in these systems.

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