The Cohen & Strand model for AP composite propellants is applied as boundary conditions , one for AP and one for binder , in solving the heat conduction equation in each to compute linear and non - linear combustion response properties for each and for the aggregate propellant . Iterations couple AP and binder through the quasi - steady flame processes . Illustrative results for linear response functions ( pressure - coupled and velocity - coupled ) are presented for a monomodal AP propellant varying AP size , pressure and crossflow speed , and examples of non - linear responses to arbitrary waveforms are shown . A quantitative comparison with response function data is limited to one well - characterized research formulation . Mechanistic implications are discussed , including recommendations for future modeling work .