Thermal Emissivity and Cigarette Coal Temperature During Smolder

Coal temperatures affect the burn properties of cigarettes. Thermal imaging was used to determine the average maximum surface coal temperatures during smolder of cigarettes of different tobacco types. The thermal imaging camera was calibrated against a reference blackbody. An emissivity correction was necessary since the set point temperatures of the reference blackbody did not correspond to the measured temperatures of the reference blackbody. A 0.87 camera emissivity was applied to provide accurate coal temperatures at a corrected emissivity of approximately 1. The average maximum surface coal temperatures during smolder of unfiltered single-tobacco-type cigarettes and a commercial blend cigarette were determined (with the camera lens focused parallel to the cigarette), and no discernible differences among them were found. The calculated average maximum surface coal temperature during smolder for all cigarettes was 584 AA± 15 °C. During smolder, thermocouples were used to measure the temperature of the gas phase (along the central axis of coal), and the thermal imaging camera was used to measure the temperature of the solid phase of the coal's surface. Using thermocouples, the peak coal temperatures in the center of the coal during smolder for three filtered single-tobacco-type cigarettes were 736-744 °C. Peak coal temperatures, measured by thermal imaging, on the surface of the coal (with the camera lens focused coaxially with the coal and the ash removed) for the same three single-tobacco-type cigarettes had a range of 721-748 °C. There was good correspondence between the two techniques. These results confirm that during smolder the gas-phase temperature inside the coal (as measured with the thermocouple) and the solid-phase temperatures beneath the ash (as measured with the camera) are in near thermal equilibrium. With proper calibration, a thermal imaging system is a good alternative to thermocouples for measuring cigarette coal temperatures.