High-Temperature Catalytic Combustion and Its Inhibition of Gas-Phase Ignition

Abstract

The emissions characteristics of the combustion of fuel-lean mixtures of methane and air were studied in steady-state conditions using two catalytic reactors: a honeycomb monolith burner and a stagnation point flow reactor (SPFR). The investigations showed that the gas-phase fuel/air mixture does not ignite until the catalytic surface is significantly above the ordinary autoignition temperature. This inhibition of gas-phase combustion by the catalytic reactions is desirable, since it extends the range over which clean and stable oxidation conditions persist. The inhibition seen in the monolith burners was observed in more detail in the SPFR experiments. The analysis of the experimental results was assisted by numerical simulations of both reactors using kinetic models consisting of heterogeneous and homogeneous elementary reactions as well as global chemical kinetic mechanisms found in the literature. The measured peak selectivity of the C-containing products was in agreement with the detailed chemical simulations. However, the latter underestimated the temperature range of the inhibition, indicating that the current description of the free radicals formation needs further investigation.