The influence of catalytic activity on the gas phase ignition of boundary layer flows Part II. Oxygen atom measurements

The process of gas phase ignition in a fuel-air boundary layer overa heated catalytic surface has been investigated using two-photon laser-induced fluorescence (LIF) measurement of oxygen atoms. The boundary layer was formed by flowing fuel-air mixtures over hot catalytic (platinum) and noncatalytic (quartz) surfaces, and simulates the entrance region of a catalytically stabilized thermal (CST) combustor. A unique optical design was required in order to eliminate interference with the fluorescence signal caused by thermal radiation from the hot surface of the plate. The O atom concentration profile data demonstrate that the platinum catalyst acts to promote the formation of oxygen atoms in the region adjacent to the surface. This effect is most apparent at lean equivalence ratios (Φ < 0.3 for ethane) where we have observed promotion of gas phase ignition by the catalytic surface. At higher equivalence ratios the ignition of ethane in air is inhibited by the platinum surface because of fuel depletion at the surface due to the mass transfer-limited catalytic oxidation reaction.