MEASUREMENTS OF HYDROXYL CONCENTRATIONS AND LIFETIMES IN LAMINAR FLAMES USING PICOSECOND TIME-RESOLVED LASER-INDUCED FLUORESCENCE

Picosecond time-resolved laser-induced fluorescence (PITLIF) can poten tially be used to obtain measurements of minor species concentrations in rapidly fluctuating flames. Previous studies demonstrated this pote ntial for atomic sodium by monitoring the temporal fluorescence signal with both an equivalent-time and a real-time sampling method. In this developmental study, PITLIF is used to determine hydroxyl concentrati ons in laminar CH4-O-2-N-2 flames by the measurement of both the integ rated fluorescence signal and the fluorescence lifetime. The quenching environment can be monitored with real-time sampling, and thus the ne cessary quenching rate coefficient is obtained in 348 us, which is fas t enough for use in many turbulent flows. Fluorescence lifetimes of OH are also measured at different equivalence ratios in laminar flames b y the use of the equivalent-time sampling technique. These results com pare favorably with predicted lifetimes based on relevant quenching cr oss sections and calculated species concentrations. (C) 1996 Optical S ociety of America