Understanding the thermal conditions inside a burning cigarette is an important step in controlling chemical emissions and also meeting reduced ignition propensity regulations. The last detailed experimental study of the thermal physics inside a burning cigarette was published more than 3 decades ago. Since then, modern commercial cigarettes have evolved considerably in designs and materials used. This study examined gas-phase combustion temperatures using Kentucky research reference cigarettes (3R4F) over two consecutive puffs taken by a smoking machine operating under the standard ISO puffing parameters. A number of thermal physical parameters (temperatures and temperature gradients in different spots versus time) were measured to characterize the alternating smoking cycle (puffing−smoldering−puffing). The dynamic distributions of coal volumes associated with different temperature ranges were measured, and a mathematical equation was used to model the distributions of volumes. Two-dimensional temperature and temperature gradient contours were constructed, which gave unparalleled insight into the heterogeneous heating of cut tobacco during cigarette burning. In addition to understanding cigarette combustion physics, the information obtained is useful in guiding analytical pyrolysis studies aimed at assessing precursor−smoke toxicant relationships and the fate of tobacco ingredients added to cigarettes.

SUMMARYAccurate measurements of cigarette coal temperature are essential to understand the thermophysical and thermochemical processes in a burning cigarette. The last systematic studies of cigarette burning temperature measurements were conducted in the mid-1970s. Contemporary cigarettes have evolved in design features and multiple standard machine-smoking regimes have also become available, hence there is a need to re-examine cigarette combustion. In this work, we performed systematic measurements on gas-phase temperature of burning cigarettes using an improved fine thermocouple technique. The effects of machine-smoking parameters (puff volume and puff duration) and filter ventilation levels were studied with high spatial and time resolutions during single puffs. The experimental results were presented in a number of different ways to highlight the dynamic and complex thermal processes inside a burning coal. A mathematical distribution equation was used to fit the experimental temperature data. Extracting and plotting the distribution parameters against puffing time revealed complex temperature profiles under different coal volume as a function of puffing intensities or filter ventilation levels. By dividing the coal volume prior to puffing into three temperature ranges (lowtemperature from 200 to 400 °C, medium-temperature from 400 to 600 °C, and high-temperature volume above 600 °C) by following their development at different smoking regimes, useful mechanistic details were obtained. Finally, direct visualisation of the gas-phase temperature through detailed temperature and temperature gradient contour maps provided further insights into the complex thermophysics of the burning coal. [Beitr. Tabakforsch. Int. 26 (2014) 191-203]

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