Modeling Gas Phase RDX Combustion with Intrinsic Low Dimensional Manifolds

The combustion of a well-stirred system of gases which result from the decomposition of cyclotrimethylenetrinitramine (RDX), a common solid explosive, is studied using the technique of intrinsic low-dimensional manifolds (ILDM). The method provides a systematic way to overcome the severe stiffness which is associated with full models of gas phase RDX combustion, and thus significantly improve computational efficiency. Here, preliminary results are shown which demonstrate the existence of an ILDM in a limited region of composition space for the isochoric, isothermal (T = 3000 K) combustion of RDX using a standard detailed kinetics model which accounts for 45 species and 232 elementary reaction steps; while the ILDM method has been used to simulate many problems in hydrocarbon combustion, this is thought to be the first application to systems which derive from solid explosives. The full model predicts the ratio of the time scale of the slowest reactions to those of the fastest reactions to reach values near 10, which indicates severe stiffness is present. The ILDM method systematically eliminates most of this stiffness by equilibrating fast time scale events and describing parametrically a low dimensional manifold upon which slow time scale events evolve. The full paper will extend the results shown here to account for adiabatic conditions, and a wider range of composition space.