Measurement and modelling of pyrotechnic time delay burning rates : application and prediction of a fast burning delay composition

Abstract

A predictive numerical model was implemented for a time delay based on the Si+Pb3O4 system. The reaction kinetic parameters were estimated by comparing predicted surface temperature profiles with experimental data acquired with an infrared camera. Fair agreement between the modelled and measured burning rates was achieved. The burning rate is predicted to increase by 9.4 % for every 50 °C increase in ambient temperature. The core diameter was found to have a slightly larger impact on the burning rate than the wall thickness. The effect of using different wall thickness materials was evaluated and indicated that the burning rate is significantly influenced by the wall material when the thermal conductivity is increased and the volumetric heat capacity is reduced. The shape of the combustion front was found to widen with a long tail for materials with a low thermal conductivity and a narrower combustion front with a short tail for materials with high thermal conductivity. Preheating occurred for pyrolytic graphite‐ and diamond‐based elements but no radial combustion was observed. The external heat transfer parameters (convection and radiation) did not affect the burning rate of the fast delay composition. It is concluded that the ambient temperature, volume fraction solids, molar heat of reaction, core and outer diameter are the factors that most significantly influence the burning rate of the Si+Pb3O4 composition in long cylindrical elements.