Predicting micro-scale wave thickness in propellant combustion

The structure of steady wave system is considered which is admitted by the continuum equations for materials that undergo phase transformations with exothermic chemical reaction. In particular, the dynamic phase front structures between liquid and gas phases, and solid and liquid phases are computationally investigated. With its theoretical basis in one-dimensional continuum shock structure analysis, the present approach estimates the micro-width of waves associated with phase transformation phenomena. For illustration purpose, n-heptane is used in the evaporation and condensation analysis and HMX is used in the melting and freezing analysis of energetic materials of interest. The estimated thickness of evaporation - condensation front of n-heptane is on the order of 10^-2 micron while the HMX melting - freezing front thickness is estimated at 1 micron. The present structure analysis is applicable to a broader range of liquid and solid propellants whose phase front thickness measurements are neither available nor experimentally attainable.