An uncoated, R-type thermocouple with a wire diameter of 75 lm and a junction diameter of about 150 lm (Omega Engineering) is used to measure temperature profiles in the sooting jet fuel flames. The thermocouple is swept rapidly into the flame and when it reaches the intended location, the temperature data are quickly recorded while the thermocouple’s emissivity and diameter are not affected considerably by soot deposition. Figure shows the configuration of the temperature measurement apparatus. This apparatus and the measurement technique used in the current study are based on an earlier work by McEnally et al.. The effect of radiation by the thermocouple junction is accounted for by equating the heat transfer into the junction by convection and the heat transfer out of the junction by radiation. Several sets of measurements were performed and averaged, making the results reproducible within 5%.