Pressure and initial temperature sensitivity coefficient calculations in ammonium perchlorate flames

A one-dimensional ammonium perchlorate combustion model including complex gas-phase chemistry is enriched by relaxing the previous assumption of constant surface temperature and implementing solid-phase thermophysical parameters to take into account the crystalline transition of ammonium perchlorate at 513.15 K. The corresponding nonlinear system of differential equations is numerically solved by using adaptive continuation techniques. Key steady-state sensitivity parameters, namely, pressure and initial temperature sensitivities of burning rate and surface temperature, are numerically obtained. These in turn allow for the investigation of unsteady issues within the framework of the Zel'dovich-Novozhilov theory. First, it is shown that intrinsic combustion instability can be triggered depending on propellant pyrolysis activation energy, gas-phase pressure, and propellant initial temperature. Second, the linear pressure-coupled combustion response function of ammonium perchlorate is obtained. Comparisons with experimental data for steady and unsteady features are systematically attempted whenever possible. It is shown in particular that quantitative comparison with experimental pressure-coupled response function data is satisfactory at 34 atm.