Natural smoulder in cigarettes

This paper contains results which are complementary to those published earlier on combustion in puffed cigarettes. Theory is presented which predicts the combustion zone shape on a diffusion controlled model. Comparison of volumetric rates of combustion in the interval between puffs and in cigarettes allowed to smoulder without puffing shows that rates of smoulder are lower between puffs. The reason for this is the phenomenon described earlier, namely ‘choking’. This is only encountered in buffed cigarettes and reduces both the rate of supply of oxygen and the volumetric rate of combustion. Experiments to determine the calorific value of tobacco and tobacco/air stoichiometry have yielded values (3 760 cal/g and 1/7· g/g respectively) making possible the calculation of the smouldering zone temperature. Comparison between the values of stoichiometry for cigarettes during the puff and during natural smoulder indicates that some 90 per cent of tobacco combustibles evades combustion during the puff.