A multizonal numerical combustion model of ammonium perchlorate

Solid rocket motors (SRM) are essential for national defense, satellite launch vehicles for placing spacecraft for communications, resource management, and space exploration. Numerical modeling of composite solid propellants is very helpful for optimizing performance, ensuring safety, and complementing experimental testing. It provides insights into combustion dynamics and allows for precise customization to meet specific mission needs, so modeling composite propellants will stay important. AP (Ammonium Perchlorate), as a synthetic oxidizer, has been widely utilized in modern composite solid propellants. Therefore, it is crucial to understand the physicochemical processes such as condensed-phase heating and reaction kinetics, the interactions between the condensed and gas phases, and gas-phase combustion. A steady-state numerical simulation model is presented to study the combustion of AP. Zonal modeling is employed to treat the solid phase, melt layer, and gas phase separately with conservation of mass, energy, and species, and the solutions are coupled with appropriate boundary conditions. A simple global reaction is developed, validated, and used for the condensed phase with better surface species profiles than those available in the literature. A detailed reaction mechanism is used in the gas phase combustion. This model considers only liquid as a condensed phase and uses a newly condensed phase mechanism and a premixed AP/HTPB (hydroxyl-terminated polybutadiene) gas phase reaction mechanism instead of AP monopropellant gas phase mechanism. This modeling is a prerequisite for a more sophisticated multi-modal composite propellant model with AP grains and AP/HTPB binder. The predicted burn rate and initial temperature sensitivities for different motor operating pressures match well with experimental and other theoretical data. Also, the simulated melt layer thickness of the present model agrees well with experimental observations. Sensitivity analysis is performed for the melt temperature and activation energy for the condensed phase reaction. The simulation also predicts surface temperature and species profile with reasonable accuracy.