CATALYTIC COMBUSTION OF HYDROGEN-AIR MIXTURES OVER PLATINUM: VALIDATION OF HETERO/HOMOGENEOUS CHEMICAL REACTION SCHEMES

Abstract

The applicability of various hetero/homogeneous chemical reaction schemes in the catalytically stabilized combustion (CST) of hydrogen/air mixtures over platinum was investigated experimentally and numerically in channel-flow configurations. The present work stems from the internationally intensified effort to commercialize power generation systems with ultra-low NOx (< 3 ppm), CST-based gas turbines. Crucial in the development of such systems is the understanding of the heterogeneous (catalytic) kinetics, the homogeneous (gas-phase) kinetics, and their respective coupling. Experiments were performed at atmospheric pressure and laminar flow conditions in an optically-accessible catalytic channel combustor: planar laser induced fluorescence (PLIF) of the OH radical was used to monitor the onset of homogeneous ignition and line-Raman measurements provided the boundary-layer profiles of the temperature and major species. Measured homogeneous ignition distances were compared against numerical predictions obtained with a two-dimensional elliptic fluid mechanical model. Six homogeneous (elementary, reduced and single-step schemes) and three heterogeneous schemes were tested in the model. The comparisons have revealed substantial differences between measured and predicted homogeneous ignition distances (ranging from 8 % to 85%) and, moreover, these differences were attributed primarily to the homogeneous reaction pathway.