Catalyzed combustion of H 2/air mixtures in a flat-plate boundary layer: I. Experimental results

Abstract

A study has been made of the combustion characteristics of lean hydrogen-air mixtures flowing over a heated catalytic platinum plate. The objectives of the investigation were to develop a better understanding of the interaction between fluid mechanics, gas-phase combustion, and surface reaction in high-temperature surface-catalyzed combustion. The experimental system consisted of a thin quartz plate with vacuum-deposited platinum heating strips mounted over an open atmospheric-pressure jet of premixed hydrogen and air. Boundary-layer density profiles were measured using differential interferometry for flow visualization studies and Rayleigh scattering for point-density measurements. Laser Doppler velocimetry was also used to measure the velocity distribution. The presence of heat release due to surface reaction was determined from changes in heating-strip power inputs with fuel addition. Results were obtained for a range of equivalence ratios from 0.05 to 0.3 and plate surface temperatures from 470 to 1300 K. Significant surface heat release was found for all mixtures at plate temperatures as low as 470 K. At increased equivalence ratios and plate temperatures heat release due to gas-phase reaction was present. This was characterized by local increases in temperature across the boundary layer and an increase in thermal boundary-layer thickness. Comparisons with numerical calculations based on a surface reaction model which included finite-rate surface oxidation of H 2 and radical recombination indicated qualitative agreement in general boundary-layer behavior, but the predicted gas-phase heat-release rate was considerably higher than found experimentally.