Modeling of Heterogeneous Propellant Combustion: A Survey

H ETEROGENEOUS solid energetic materials are widely used in the aerospace and defense industries in rockets, explosives, and diverse pyrotechnic devices. Their basic microstructure consists of oxidizer particles embedded in a polymeric binder. Two important classes of energeticmaterials are solid propellants and plastic bonded explosives. A typical composite solid propellant is composed ammonium perchlorate (AP) particles embedded in a polymer such as hydroxyl-terminated polybutadiene (HTPB) or polybutadiene acrylonitrile. A common variation is the addition of metal particles (e.g., aluminum) to raise the combustion temperature. Plastic bonded explosives consist of a heterogeneous mixture of high-explosive crystals (such as cyclotetramethylenetetranitramine or cyclotrimethylenetrinitramine) and a polymeric binder. Here, the discussion is restricted to composite solid propellants. The intent of the present survey is to provide a highlighted discussion of relevant work on the multidimensional computational simulation of heterogeneous solid propellant combustion. Routine numerical simulations are now being carried out, in which many of the physical characteristics of real propellants are mimicked, including random packing of oxidizer particles in a fuel binder, unsteady three-dimensional heat conduction within the solid, unsteady regressionof thenonplanar propellant surface, andcoupling with an unsteady three-dimensional combustion field sustained by reactantfluxes from the surface. Such computations require the use of massively parallel supercomputers, and even then there are limitations onwhat physics can be included. The ultimate goal is to develop a truly predictive simulation tool that can assist in design and optimization of propellant microstructures and propellant grain designs for internal solid rocket motors. Modeling and simulation of composite propellants will remain a vital task because solid rocket motors are critical to national defense, communications, space exploration, and eventually space tourism. The value of computational combustion is eloquently presented in a recent review paper [1]. II. Modeling