Effect of wall thermal conductivity on the heterogeneous combustion of hydrogen-air mixtures over platinum in catalytic micro-combustors

The hetero-/homogeneous combustion of hydrogen-air mixtures over platinum in catalytic micro-combustors were investigated numerically and experimentally. Experiments were performed in a catalytic channel-flow micro-reactor. Catalysts consisting of platinum supported on alumina powder were prepared and tested. Numerical simulations were carried out with a two-dimensional computational fluid dynamics model in conjunction with detailed heterogeneous and homogeneous reaction mechanisms. Specific objectives are to study the effects of combustor wall conductivity on heterogeneous combustion characteristics and the steady-state, self-sustained flame stability of hydrogen-air mixtures. Hydrogen-air heterogeneous flame is found that it can be stabilized in narrow channels but very careful design is necessary. Large axial and transverse gradients are observed even at these small scales under certain conditions. Wall thermal conductivity is vital in determining the flame stability of the system, as the walls are responsible for the majority of the upstream heat transfer as well as the external heat losses. Hydrogen heterogeneous flames are more robust than methane heterogeneous flames. The catalytic self-ignition nature of hydrogen-air mixtures offers an opportunity to catalytic self-ignite hydrocarbons, resulting in a way toward elimination of ignition sources from micro-scale devices. Design recommendations are made, engineering maps denoting flame stability are constructed, and comparisons with methane-air systems are made