Combustion of sandwich propellant at low pressures

This article presents the results of both experimental and computational studies that were carried out at pressures close to atmospheric pressure (in numerical studies, the pressure range was from 0.078 to 1.4 MPa) to obtain an insight into the behavior of pure ammonium perchlorate (AP)–hydroxyl terminated poly butadiene (HTPB) sandwich propellant at these conditions. Numerical studies were carried out for a periodic sandwich propellant configuration with a two-dimensional unsteady model in both the gas and condensed phases accounting for the non-planar nature of the regressing surface. Appropriate boundary conditions across the gas–solid interface which lead to correct coupling of the gas phase with the condensed phase have been utilized. The three-step gas phase chemical kinetics model along with a surface decomposition model for AP and a surface pyrolysis model for fuel were utilized. The binder thickness used in these studies varied from 10 to 400 μm. The numerical study has successfully captured the splitting of the base of the flame observed at large binder thicknesses. The quenching of sandwiches has been experimentally observed and has been successfully predicted as well. The predicted pressure index of combustion of sandwiches indicated two different indices in different pressure regimes consistent with experimental observations. The predicted pressure index was 0.4 for pressures up to 0.7 MPa and for pressures greater than 0.7 MPa it was 0.74.