Abstract
The draw resistance of a cigarette increases by about 50-60 % when the cigarette is lit, and the total draw resistance of the burning cigarette varies in a distinct manner as it is smoked. This effect is not normally due to an inherent increase in the impedance of the coal, because the effect disappears when the cigarette is extinguished. Rather, the effect is due to the heating of the gases flowing through the coal and down the tobacco rod, in particular (a) the increase in gas viscosity with temperature, (b) the increase in volumetric gas flow due to thermal expansion, and (c) the increase in the impedance of the unburnt tobacco rod, due to the deposition of smoke condensate on the rod. A hot-gas model, using the above contributing factors together with the known gas-phase temperature distribution inside the burning cigarette, can predict quantitatively (within the limits of experimental error) the observed variations of the draw resistance of a burning cigarette.