Investigation on burning rate–pressure mechanism of octogen-based charge considering venting effect

Venting openings are widely employed to mitigate catastrophic accidents caused by accidental charge ignition. However, the vented combustion behavior of charges remains insufficiently understood, resulting in limited theoretical guidance for vent design and vent opening pressure thresholds. In this study, a numerical model incorporating combustion characteristics governed by a pressure-modified Arrhenius equation was developed based on previously reported confined combustion experimental data of charges consisting of 87% octogen (HMX) and binder. By combining numerical simulations with theoretical analysis, we found that the temporal variations of chamber temperature and vent inlet velocity are primarily governed by vent size and are nearly independent of vent opening pressure. This is attributed to the quasi-uniform thermodynamic field inside the chamber and the establishment of choked flow at the vent. Furthermore, the rapid decrease in chamber pressure and temperature during vented combustion significantly weakens thermal feedback to the burning surface, so the pressure–burning rate relationship deviates from the classical Vieille law and is better described by a quadratic function. In addition, critical criteria for venting failure were established based on both mass flow balance and energy balance. The predictions obtained from the two approaches show good agreement and enable determination of the minimum vent size required for charge and munition structural design. The above-mentioned findings provide the theoretical support for vent design and the delineation of safe zones during charge venting, thereby contributing to improved safety and hazard mitigation performance of energetic systems.