The dependence of critical heat flux on fuel and additive properties: a critical mass flux model

Abstract

We use a mathematical model for the ignition of thermally thin thermoplastics to evaluate the critical heat flux, and the corresponding critical surface temperature, required for piloted ignition by using the concept that a sample ignites when the mass flux of fuel from the solid into the gas phase reaches a critical value. We show how the critical heat flux is related to the ‘characteristic temperature’ determined in thermogravimetric experiments (TG) and investigate how this value is affected by dilution of the fuel with an inert additive and by the addition of a heat-sink additive. We suggest that experimental results should be presented in terms of a dilution factor rather than by the usual ‘% weight additive’. The specific application of the model we have in mind is piloted ignition in the cone calorimeter.