Simulation of hetero/homogeneous combustion characteristics of CH4/air in a half packed-bed catalytic combustor

The catalytic combustion of CH4/air mixtures in a half packed-bed combustor was investigated numerically to acquire the hetero/homogeneous combustion characteristics. Three combustion modes: completed heterogeneous combustion, hetero-homogeneous combustion, and incomplete heterogeneous combustion are discovered and investigated, respectively under low (0.05-1.53 m/s), middle (1.53-8.7 m/s), and high (8.7-12.4 m/s) inlet velocity. Under middle inlet velocity, heterogeneous reaction triggers homogeneous reaction downstream. The interface between catalyst and gas-phase zones was analyzed to reveal the effects of the upstream heterogeneous combustion on the trigging of downstream homogeneous combustion. Three zones in the interface: burned zone, transition zone and unburned zone, were defined and analyzed. A parameter of transition zone in the interface, Gamma was defined to evaluate the level of temperature gradient versus inlet velocity. When Gamma < 0.011, homogeneous combustion is not trigged due to the relative weak heterogeneous combustion which brings downstream gases unfavorable conditions. (C) 2019 Elsevier Ltd. All rights reserved.