HCO concentration in flames via quantitative laser-induced fluorescence

Quantitative laser-induced fluorescence (LIF) measurements of the concentration of HCO are made in three 25-torr methane-oxygen-nitrogen flames: fuel lean (φ=0.81), near stoichiometric (φ=1.07), and fuel rich (φ=1.28). LIF is excited in the (000)-(000) band of the B-X system near 258 nm. The LIF signal from the flame is calibrated against nonflame measurements of a known HCO concentration produced by laser photolysis of acetaldehyde. The LIF signal is adjusted for the variation in the fraction of the population of the laser-excited level as the measured temperature changew with position in the flame and for the measured variation in quenching. The resulting concentration measurements agree well with model predictions for the fuel-lean and near-stoichiometric flame. The measurements in the fuel-rich flame are significantly larger than the model predictions: however, these measurements are subject to increased uncertainty due to the large, broadband background in the rich flame.