Numerical investigations on characteristics of methane catalytic combustion in micro-channels with a concave or convex wall cavity

• Micro-channel with convex cavity is more benefit for catalytic combustion than that with conventional concave cavity.
• When the equivalence ratio of mixture increases from 0.8 to 1.2, the conversion first increases then decreases in all cases.
• In the micro-channel with convex wall cavity, the inner wall pressure increases which favors the combustion.
• Heat transfer in the convex micro-channel is enhanced which makes the temperature distribution more uniform.
• Extinction limit extends in the micro-channel with convex cavity, which is 16.5 m/s.

Catalytic combustion characteristics of methane in micro-channels with a concave and convex cavity, respectively, and in straight channel without cavity were numerically investigated. The results show that as the equivalence ratio (ϕϕ) increases, the methane conversion increases first and then decreases, the highest methane conversion ratio, which is 85.3%, occurs at ϕϕ = 1.0 in the micro-channel with convex wall cavity. The micro-channel with concave wall cavity is not conductive to methane catalytic micro-combustion at relatively low velocity. With the inlet velocity increasing, the methane conversion ratio is decreased. In the micro-channel with convex wall cavity, the inner wall pressure increases, because the fuel is disrupted when it flows through the cavity. Then the mixture of methane contact with catalyst is enhanced, which favors the combustion of methane. The recirculation zone which is the largest area formed in the micro-channel with convex wall cavity absorbs more high temperature gas and raises the combustion temperature. Heat transfer in the convex micro-channel is enhanced which makes the temperature distribution more uniform. The maximum value of the extinction limit is 16.5 m/s, which occurs in the micro-channel with convex cavity.