Exciplex Fluorescence Thermometry of Falling Hexadecane Droplets

Exciplex fluorescence thermometry has been used to measure the temperature of 283 micron hexadecane droplets falling through a quiescent, oxygen-free, approximately 500°C ambient. After a period of negligible change, the derived droplet temperatures exhibit a sharp rise of about 100°C followed by a gentle increase to approximately 200°C. The derived temperatures, although averaged over most of the volume of the droplet, still provide some evidence of internal processes in the droplet due to the partially selective optical sampling of the droplet volume, in which fluorescence from the region between 0.50 and 0.75 of the droplet radius contributes disproportionately. At longer times, the droplet is presumed to be approximately homogeneous, and the exciplex fluorescence thermometry measurements provide accurate, interpretable temperatures for the freely falling droplets.