A numerical investigation on non-premixed catalytic combustion of CH4/(O2 + N2) in a planar micro-combustor

•Partially premixed catalytic combustion in a micro-combustor was numerically studied.•Heat release rate rises first and then decreases with an increasing inlet velocity.•The combustion efficiency shows a non-monotonic variation against combustor height.•Slightly fuel-rich condition can enhance heterogeneous reaction on the oxidant side.•Oxygen enrichment can significantly enhance both homo- and hetero-geneous reactions. Non-premixed catalytic combustion in micro-combustors has not been reported so far. The present study demonstrates the feasibility of non-premixed CH4/(O2 + N2) catalytic combustion in a planar micro-combustor with a height less than the quenching distance. The impacts of inlet velocity, combustor height, nominal equivalence ratio and O2 concentration on the combustion characteristics were numerically investigated. First, it is found that with the increase of inlet velocity, the catalytic reaction zone moves downstream and the reaction intensity increases first and then decreases. Second, as the combustor height is increased, the catalytic reaction zone broadens and the largest heat release rate decreases, while the maximum temperature and combustion efficiency show non-monotonic variations. Thirdly, a slightly fuel-rich condition can increase Pt(s) coverage, enhance catalytic reaction on the oxidant side, and improve combustion efficiency. Finally, oxygen enrichment can significantly enhance both heterogeneous and homogeneous reactions, leading to a dramatic improvement in combustion efficiency.