ABSOLUTE TEMPERATURE-FIELDS IN FLAMES BY 2D-LIF OF OH USING EXCIMER LASERS AND CARS SPECTROSCOPY

A tunable KrF-excimer laser was used to obtain temperature fields in a laminar, premixed atmospheric pressure flame by 2D-LIF of OH. Relative temperatures were obtained first from the intensity ratio of two sequentially excited rotational lines of the OH (A2SIGMA+ - X2PI) transition in the (3-0) band near 248 nm. Because the upsilon' = 3 level is predissociative, this excitation scheme is less sensitive to collisional quenching than lower vibrational levels of OH (A2SIGMA+). Fluorescence from lower lying, non-predissociative vibrational levels of OH (populated by vibrational transfer) was effectively suppressed by narrow spectral filtering of the (3-2) band of OH. Absolute temperatures were determined by calibration at one point with broadband CARS measurements; the excellent agreement of LIF and CARS profiles suggest that for these conditions and at the present level of accuracy no further corrections are needed. The uncertainty in the 2D-LIF measurements of 7% (for a spatial resolution of 300 mum) is due mainly to shot-to-shot fluctuations of the beam profile. Based on the photon shot noise contribution (less than 1%), we estimate that, provided the beam energy and profile are accounted for, single-shot measurements should be feasible with a spatial resolution of 300 mum and a precision of 2%.