Extinction limits of catalytic combustion in micro-channels

The limits to self-sustaining catalytic combustion in a micro-scale channel were studied computationally using a cylindrical tube reactor. Methane-air mixtures with average velocities of 0.0375-0.96 m/sec were used. When the wall boundary condition was adiabatic, the equivalence ratio at the extinction limit monotonically decreased with increasing Re. In contrast, for non-adiabatic conditions, the extinction curve exhibited U-shaped dual limit behavior, i.e., the extinction limits increased/decreased with decreasing Re in smaller/larger Re regions, respectively. Diluting the mixture with N₂ rather than oil, the fuel concentration and peak temperatures at the limit decreased substantially for mixtures with fuel/oxygen ratios even slightly rich of stoichiometric due to a transition from O coverage to CO coverage. No corresponding behavior was found for non-catalytic combustion. Exhaust gas recirculation rather than lean mixtures are preferable for minimizing flame temperatures in catalytic micro-combustors. Original is an abstract.