Experimental and Numerical Characterization of the Influence of a Smoldering Cellulosic Substrate on a Cigarette’s Ignition Propensity Test

Abstract

An experimental and numerical investigation was conducted to characterize the influence of the cellulosic substrate used to assess the ignition propensity (IP) of cigarettes. Such an IP test is currently prescribed by the ISO 12863 standard and its results typically show poor repeatability. It is believed that such a low reproducibility is mainly due to the variability of the cigarette itself but it is unclear as to what extent the substrate also influences the variability of the test results. Therefore, the objective of this investigation was to analyze the potential influence of the substrate by first characterizing the thermodynamic behavior experimentally and then constructing a numerical model that can quantify the relative influence of the distinct parameters. A suite of experimental methods that included TGA, DSC, infrared measurements and laser triangulation among others was used to measure the thermophysical properties of the substrate. These properties were then used to build a CFD model that simulated the smoldering combustion experienced by the substrate during the IP test. After validating the model against contactless temperature measurements, a parametric study consisting of 363 IP simulations was performed, which served to quantify the relative importance of 13 thermophysical parameters when varying in ranges of about 5%–50%. The results indicated that the heat capacity, pyrolysis activation energy, and air gap thickness are the most influencing aspects of the substrate because they influence the heat absorbed by the substrate about 7%, 26% and 33%, respectively. The latter parameter was found to significantly vary with each test and its influence was comparable to that of some major properties of the cigarette such as the cigarette’s temperature and burning rate. It is therefore postulated that the variability of the substrate itself plays an important role on the poor repeatability of the test and it may comprise its reliability.