Exploiting EM Thermal Decomposition Kinetics forSimulating Combustion and Explosions

摘要

Traditional types of thermal analysis experiments can be used, with care, to determine the global thermal decomposition kinetics of energetic materials (EM). Because all explosives and propellants are designed to produce gas and heat, it is natural that thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are two of the workhorse techniques for this type of work. In previous reports, we have described the development of both model-free and model fitting approaches to the task of extracting reliable values of kinetic parameters for these reactions, as well as robust estimates of the associated uncertainties. Kinetic parameters can be a useful diagnostic for solving problems in combustion. The presence of impurities in FOX-7, an advanced insensitive explosive, can be detected as anomalous changes in activation energies for thermal decomposition of the material. These changes are readily detected using model-free kinetic analysis of activation energy as a function of the extent of thermal decomposition for milligram samples in laboratory-scale TGA experiments. Thermal decomposition kinetic parameters can also be used in computational models of combustion of energetic materials, particularly for describing the overall rate of conversion of solid to gas. Such a model has been developed for combustion of the plastic-bonded explosive PBX9501. The model is based on a simplified kinetic scheme for combustion developed by Ward, Son and Brewster. When used in high-performance computer simulations of explosions, the results reveal some of the dependence of explosion violence on device geometry and heating rate. Specifically, we have investigated external heating and explosion of steel containers of PBX9501, such as might be caused by a transportation accident. At moderate heating rates, the incorporation of a hollow bore in the device greatly increases the violence of the explosion, as measured by the velocity of the steel fragments. The simulations are in good qualitative agreement with experimental measurements.