EFFECT OF WALL THERMAL CONDUCTIVITY ON MICRO-SCALE COMBUSTION CHARACTERISTICS OF HYDROGEN-AIR MIXTURES WITH DETAILED CHEMICAL KINETIC MECHANISMS IN Pt/γ-Al2O3 CATALYTIC MICRO-COMBUSTORS

To understand the effect of different thermal conductivities on catalytic combustion characteristics, effect of thermal conductivity on micro-combustion characteristics of hydrogen-air mixtures in Pt/γ-Al2O3 catalytic micro-combustors were investigated numerically with detailed chemical kinetics mechanisms. Three kinds of wall materials (100, 7.5, and 0.5 W/m·K) were selected to investigate the effect of heat conduction on the catalytic combustion. The simulation results indicate that the catalytic reaction restrains the gas phase reaction in Pt/γ-Al2O3 catalytic micro-combustors. The gas phase reaction restrained by Pt/γ-Al2O3 catalysts is sensitive to thermal boundary condition at the wall. For most conditions, the gas phase reaction cannot be ignored in Pt/γ-Al2O3 catalytic micro-combustors. For low thermal conductivity, the higher temperature gradient on the wall will promote the gas phase reaction shift upstream; high temperature gradient exists on the wall, and the hot spot can cause the material to melt or degrade the catalyst. Due to the gas phase reaction is ignited and sustained in micro-combustors by the heat from the catalytic reaction, the effect of thermal conductivity on micro-scale combustion characteristics is not as obvious as it is in micro-combustors without Pt/γ-Al2O3 catalysts.