Modeling of partially confined hot fragment conductive ignition

The purpose of this work is to establish a comprehensive theoretical model for studying the degree of vulnerabilityof nitramine-based propellants subjected to hot fragments within a partially confined enclosure. The model simulates the complicated processes of heat transfer and displacement of the hot fragments, generation of a foam layer caused by liquefaction and decomposition of the propellant, and regression of the propellant. A lumped-parameter analysis is considered for the determination of instantaneous temperature, pressure, and species concentrations of the gas phase within the enclosure. A reduced chemical kinetic scheme for RDX decomposition has been adopted to simulate the chemical reactions at the propellant/foam layer interface, the foam layer, and gas-phase regions. The developed model has been used to study the effects of initial temperature of hot fragment, size of hot fragment, and size of chamber exhaust port on ignition of XM39 propellant. The go/no-go ignition boundary of the highly confined case was found to be lower than that of a partially confined condition by about 150 K and is in good agreement with data obtained from experiments. This is mainly caused by the fact that under highly confined conditions, the accumulation of pyrolysis products and results chamber pressurization significantly enhance the exothermic heat release associated with the gas-phase reactions between CH₂O and NO₂ species.