Modeling of a smoldering cigarette

Abstract

A transient 2D model based on the first principles has been developed for the natural smoldering of a cigarette. The domain is assumed to be 2D and axisymmetric. Heat transfer is represented by the use of a two-temperature formulation whereby the solid and gas phases are considered to have separate and distinct temperatures interacting through an inter-phase heat exchange. The starting material first undergoes pyrolysis prior to oxidation of the remaining carbonaceous residue. The pyrolysis is assumed to consist of a set of four reactions. Oxidation of the carbonaceous residue is accompanied by the formation of gas-phase combustion products, whose concentration is also computed. The change in the tobacco rod permeability due to combustion is modeled using a single step dependence on the solid density. Calculations under unsteady conditions are done for a variety of smoldering cases with varying operating and boundary conditions. The model was validated by comparing the predictions with the experimental data on the smoldering burn rate and the maximum gas and solid temperatures. The computation captures the development of a steady combustion regime in which the burn front moves at a constant rate. More information can be obtained from the model including coal shape, gas and solid temperature profiles, product yields, solid density variations, and the effects of ignition conditions. The results are shown to be very sensitive to the availability of oxygen, and consequently to the oxygen diffusivity through the cigarette paper.