The influence of catalytic activity on the ignition of boundary layer flows Part I: Hydroxyl radical measurements

Abstract

The effect of catalytic activity on gas phase ignition in an ethane-air boundary layer was investigated by measuring OH concentration profiles over heated platinum and quartz surfaces. Platinum's catalytic influence on gas phase ignition was found to depend strongly on the fuel-air ratio. Experiments were performed in a flat plate boundary layer configuration at 1 atm pressure and surface temperatures of 1200–1650 K. The hydroxyl measurements were made by planar and pointwise laser-induced fluorescence. Inhibition of ethane-air ignition was observed at equivalence ratios greater than 0.35, with enhancement seen below this value. Depletion of fuel near the catalytic surface by mass transfer-limited oxidation reactions can account for the catalyst's inhibiting effect. Catalytic promotion of gas phase ignition was evidenced by significantly higher OH concentration levels over platinum plates (as compared to quartz) for the leanest equivalence ratio tested (Φ = 0.079). The results indicate that catalytic surface-induced production of active intermediates can promote gas phase ignition and offset the effect of reactant depletion near the surface.