Ignition dynamics of fully reactive propellant in stagnation flow

Abstract

The ignition dynamics of a reactive homogeneous propellant immersed in a hot, reactive, low subsonic flow is solved numerically for the stagnation point. The solution includes the entire ignition process from the onset of the flow to the attainment of steady burning under steady flow. The gas phase equations are of the nonsteady boundary-layer type, including freestream nonsteadiness. The reactive gas phase is coupled to the reactive condensed phase which has reactant depletion and surface regression. Ignition delay times and dynamics are calculated for variations in flow velocity, pressure, temperature, freestream oxidizer content, condensed phase activation energy and heat of reaction, and initial propellant temperature. The transition from one steady burning state to another after a pressure pulse is also investigated. Conditions are identified when dominance shifts from the condensed phase to the gas phase. Excursions of the condensed phase reaction front cause fluctuations of the surface temperature (hence, regression rates) before steady burning. In marginal cases (e.g., low initial propellant temperature), the excursions trigger a low-frequency, ignition-extinction sequence.