Numerical investigation on combustion characteristics of methane in a hybrid catalytic combustor

Combustion characteristics of a hybrid catalytic combustor, which consists of a catalyst bed and a thermal combustor section, were investigated using two-dimensional boundary layer approximations with detailed homogeneous and heterogeneous chemistries. Lean methane-air mixture was supplied to the inlet of a catalyst bed section. In order to validate our numerical analyses, the surface site density of platinum-coated monolith was estimated through the comparisons with the experimental data reported in literature. Discussed in detail were the effects of homogeneous chemistry and heterogeneous chemistry on catalytic combustion characteristics. The extensive numerical calculations performed with the selected surface site density revealed that homogeneous reactions in the monolith had little effects on the spatial distributions of temperature and CH4 conversion and the location of heterogeneous ignition, while they showed an important role to the initial reaction processes in the thermal combustor section through productions of the significant amount of intermediate species, such as OH and CO, near the catalyst bed exit. The parametric study for various operating conditions, such as equivalence ratio, temperature, velocity, entrance diameter of the monolith channel and inlet pressure, were also performed to investigate their effects on catalytic combustion. In the thermal combustor, N2O was a dominant component in emissions that are mainly formed under the reaction mechanism, N2+O(+M)→N2O(+M), in case no additional fuel is injected. Furthermore, the formations of CO and NOx emission were also characterized with controlling the amount of additional methane injection to the thermal combustor.