Flame zone and sub-surface reaction model for deflagrating RDX

Abstract

A study of 1,3,5 Trinitro Hexahydro 1,3,5 Triazine, RDX, burning as a monopropellant was undertaken to obtain a better understanding of the important chemical steps that control heat feedback to the condensed phase, to determine the contributions of the liquid layer, and to provide a means of evaluating theories for modifying the burning rate of nitramines. The following chemical mechanism is proposed: first, partial decomposition of the RDX molecule in the liquid phase; second, following vaporization, gas phase decomposition of RDX; third, oxidation of formaldehyde by NO2. The flame structure and liquid layer reactions of deflagrating RDX were expressed in terms of the energy, continuity, and species equations corresponding to RDX decomposing in liquid and gaseous phases and the NO2/CH2O reactions adjacent to the surface. In addition to the temperature profile and burning rate, the numerical solution provides the details of the interactions at the liquid/gas interface and the concentration profiles for the nine most prominent species. Using published kinetic data, the calculated results reveal that even though the liquid layer becomes thinner with increasing pressure, the increase in surface temperature causes its heat feedback contribution to increase. The pressure sensitivity of burning rate between 0.7 and 0.8 is interpreted in terms of the relative contributions of gas phase and liquid layer RDX decomposition and the oxidation of CH2O. In particular, as pressure increases, the contribution from liquid layer reactions and the second order, NO2/CH2O reaction become more prominent.