Imaging of the oxygen distribution in an isothermal turbulent free jet using two-color toluene LIF imaging

Abstract

The results of a novel technique for the quantification of oxygen in an isothermal turbulent free jet using toluene laser induced fluorescence (LIF) are presented. This method relies on the red-shift of the toluene LIF emission spectrum with increasing oxygen concentration. Evaluating the LIF signal ratio from two different wavelength regions simultaneously produces results that depend only on the local oxygen concentration. From calibration data, obtained from repeated tests, the oxygen sensitivity of the two-color LIF technique is best for oxygen partial pressures $p_{\mathrm{O}_{2}} \leq 120\mbox{ mbar}$ in the current setup. Quantified images of oxygen distribution are presented for 40.4, 60.5, 80.5, and 103 mbar $p_{\mathrm{O}_{2}}$ in the toluene-seeded jet flow that is shielded by a toluene-seeded nitrogen co-flow at atmospheric pressure and temperature. Based on the average oxygen concentration images (obtained from 100 instantaneous oxygen images), the error in accuracy of measuring the oxygen concentration was 0.8, 3.0, 7.7, and 7.3% with a precision of ± 8.6, 5.5, 13.3, and 11.6% for the jet $p_{\mathrm{O}_{2}} = 40.4,\, 60.5,\, 80.5,\mbox{ and }103\mbox{ mbar}$ cases, respectively. The main jet flow characteristics have been captured by the technique as determined from the measured oxygen distribution images. Centerline profiles of average oxygen concentration, normalized to the value at the nozzle exit, demonstrate self-similar behavior from 5 mm above the nozzle exit. Radial oxygen concentration profiles exhibit a Gaussian-type distribution that broadens with distance above the nozzle exit, in agreement with literature.