QUENCHING EFFECTS ON LASER-FLUORESCENCE MEASUREMENTS OF OH ROTATIONALTEMPERATURE IN H-2 O-2/AR FLAMES/

The OH rotational temperature profiles in a series of low-pressure (76 -torr) H-2/O-2/Ar flames (Phi = 0.88, 0.98, 1.22, 1.37, and 1.50) were measured via laser-induced fluorescence (LIF) from the A(2) Sigma - X (2) Pi transition in the OH molecule. The temperature measurements wer e obtained from temporally integrated two-line fluorescence from the O H (1,1) band at 314.5 nm with excitation in the OH(1, 0) band from eit her the Q(1)(3) or Q(1)(7) line. Time-resolved fluorescence measuremen ts of the quenching rates for these transitions were used to correct t he two-line fluorescence signals for viriation in fluorescence yield. The two-line fluorescence temperature measurement technique was calibr ated with fluorescence excitation spectra in the R(1) branch of the (1 , 0) band, which were also corrected for variation in quenching. The r otational-level-dependent quenching rates decreased as much as 25% as the excited-state rotational level increased from N' = 4 to N' = 11. O ver the range of equivalence ratios that were studied, the inclusion o f the quenching correction in the analysis lowers the measured rotatio nal temperatures by as much as 150 K, compared to an analysis that ass umed a constant fluorescence yield. Neglecting rotational-level-depend ent quenching can introduce a systematic error in OH LIF temperature m easurements as much as 10% in the temperature range from 1000 to 1500 K.