| Combustion on and near catalytic surfaces has been investigated using laser diagnostics and numerical modeling. Two effects have been examined in detail—the effect of a catalyst on post-flame gases, and catalytic combustion. A low pressure, axisymmetric stagnation-point flow system is used for all studies. Laser-induced fluorescence (LIF) has been employed to measure the concentrations of OH and NO under various combustion conditions. Rayleigh scattering and LIF are used to measure temperatures. The Sandia code SPIN is used for the solution of the coupled fluid-flow-chemistry problem and detailed descriptions of the surface and gas-phase chemistry are used.; Near-surface laser-induced fluorescence (LIF) measurements of OH are performed in the post-flame region of low pressure hydrogen/oxygen flames in stagnation flows above catalytic and non-catalytic surfaces. Measurements of the normalized gradient of the OH number density near the surface are shown to be sensitive to changes in surface reaction rates, and thus can be used as a test of surface chemical mechanisms. The results suggest that the recombination probability of OH on platinum is generally overpredicted by current surface models, and that the dependence of recombination on pressure is stronger than predicted. A higher sticking probability of O2 on Pt is suggested.; Experimental NO profiles in H2/O2/NH3 stagnation point flames over platinum substrates are obtained with laser-induced fluorescence for a range of flame equivalence ratios and substrate temperatures, and compared with model. A currently popular surface chemistry mechanism, provides good agreement with the experimental results for only a limited range of operating conditions. At low temperatures, the mechanism underpredicts NO removal, while at high temperatures and very fuel-lean conditions the mechanism overpredicts NO destruction. Some variations to the baseline model, that shift the predicted profiles closer to those observed in the experiment, are discussed.; Profiles of artificially added NO are monitored by LIF during catalytic combustion on platinum and palladium. Substantial destruction of NO is observed including under conditions where oxygen is present in large excess (based on inlet gas-phase stoichiometry). The mole fraction of NO decays by up to 85% in the vicinity of the substrate, and a significant effect is seen on both catalysts from fuel equivalence ratios of 0.5 to 1.2. The results from this study indicate that NO removal steps must be incorporated in the surface chemistry for accurate predictive capabilities. |
