Calibration-free imaging thermometry via two-line atomic fluorescence in combustion processes

Abstract

In this Letter, we demonstrate, for the first time (to the best of our knowledge), calibration-free imaging of full-frame temperature fields for particle-laden flames using two-line atomic fluorescence (TLAF) of indium. Measurements were carried out in laminar premixed flames with indium precursor aerosol added. The technique is based on the excitation of the 52P3/2 → 62S1/2 and 52P1/2 → 62S1/2 transitions of indium atoms and the detection of the subsequent fluorescence signals. To this end, the transitions were excited by scanning two narrowband external cavity diode lasers (ECDL) over the transition bandwidths. To achieve imaging thermometry, the excitation lasers were formed into a light sheet of 1.5 mm width and 24 mm height. Employing this setup on a laminar, premixed flat-flame burner, temperature distributions were measured for various air:fuel ratios of 0.7, 0.8, and 0.9. The presented results demonstrate the capability of the technique and encourage further developments, e.g., for its future use in flame synthesis of nanoparticles containing indium compounds.