Thermally Assisted Fluorescence: A New Technique for Local Flame Temperature Measurement

Abstract

The theoretical basis of a new technique called thermally assisted atomic fluorescence for measurement of local spatial-temporal flame temperatures is given. In this method, the ratio of fluorescence signals from a radiatively excited level and a higher collisionally excited level or from two higher collisionally excited levels of an inorganic probe, such as In or TI, is related to the flame temperature. The conditions necessary for the measured flame temperature to be identical to the translational (Boltzmann) flame temperature are given. The experimental system and conditions for making flame temperature measurements, which consists basically of a single pulsed dye laser and a gated detector, are described. The assumption of steady-state conditions is discussed as well as several anomalies in terms of fluorescence from certain energy levels of Tl. The accuracy and precision of the measured flame temperatures for several methane-air flames are discussed.