A simplified model for composite propellant burning rate

A combustion model has been formulated to solve the burning rate eigenvalue problem for a model composite solid propellant, similar to what has been done previously for homogeneous energetic solids. a two-step reaction [sequence (high activation energy condensed phase decomposition followed by low activation energy gas phase heat release) has been extended from one to two dimensions for non-premixed (heterogeneous fuel/oxidizer) composite solids. Gas phase streamwise diffusion, the primary driving force for solid pyrolysis, has been accounted for by including a finite value of the Peclet number. Two possible gas phase reaction schemes, one dependent only upon oxidizer mass fraction, and the other a function of both oxidizer and fuel concentration are considered. The results show that the value of the Peclet number, a non-dimensional burning rate, is constrained to a reasonably small interval by the eigenvalue expression obtained from activation energy asymptotic analysis of the condensed phase thermal decomposition zone. The present model is limited to propellants in which diffusion flame and particle size effects are minimal such as nitramine composites, but the approach is amenable to more complex chemical kinetics as they become known.