Solid rocket propellants can be ignited by electrostatic discharge (ESD) events delivering energies orders of magnitude below those typically required to cause ignition. Confinement effects have been proposed as the cause of increased sensitivity to ignition. To better understand the factors influential in ESD ignition, a model for confined ignition of propellants was developed. This model integrates time-dependent, one-dimensional energy and mass conservation equations describing a propellant block with combustion inside an enclosed gas pocket. The model includes the effects of confinement through submodels for linear elastic crack expansion and propagation and for venting of gases following rupture of the propellant block. Parametric studies were performed with the model using properties of a typical solid propellant. In agreement with experimental observations, these studies showed that external pressure has a dramatic effect on ignition sensitivity. The studies also identified propellant properties that have a significant impact on ESD confined ignition sensitivity: burn rate, activation energy of the solid-phase decomposition reaction (through its effect on burn rate), modulus of elasticity, and fracture toughness. Relatively unimportant properties include discharge volume, crack propagation velocity, and energy delivery time.
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