Development of gas-phase reaction mechanisms for nitramine combustion

A methodology for developing gas-phase reaction mechanisms for nitramine propellants is discussed. Examples of fundamental kinetic experiments and detailed modeling calculations are given that emphasize a hierarchical construction procedure for both types of experiments necessary for collecting kinetic data and the specific chemical submodels that need to be studied. In particular, three kinetic submodels of increasing complexity are described with selected results from flow reactor experiments. With kinetic data generated from these experiments and others, chemical submodels are developed and validated by comparison of model predictions with experimental measurements using reaction flux and sensitivity analyses to guide the process. Collectively, the submodels, validated over the entire range of experimentally studied conditions, are assembled to form the gas-phase nitramine combustion mechanism. Because of the nature of the developmental procedure, e.g., the necessity for different types of experiments, ranging from 'microscopic' measurements of isolated reaction rate constants to 'macroscopic' studies on kinetic mechanisms in flames, the process is inherently iterative. As an example of this iterative procedure, numerical results are presented on the ignition behavior of RDX after updating a previously developed model with recent results from submodel validation experiments. These results show changes in the pathways of many secondary species involved in RDX decomposition. (Author)