Effect of Chamber Pressure and Propellant Composition on Erosion Rate of Graphite Rocket Nozzle

Abstract

The objective of this work is to study the nozzle erosion rates at a broad range of pressures from 7 to 55 MPa with two baseline propellants: one is a nonmetallized propellant and the other is a metallized propellant, called propellants S and M, respectively. A comprehensive model for graphite nozzle erosion minimization and a numerical code has been advanced to predict the nozzle throat recession rates at high pressures. Four different kinetic schemes for heterogeneous graphite oxidation reactions were compared. The recession rate was found to increase almost linearly with pressure. The magnitudes of recession rates depend on the chemical kinetic scheme and the propellant composition. Contrary to popular belief, at lower pressures (P < 14 MPa), the heterogeneous kinetic rates showed a pronounced effect on the erosion rates, though at higher pressures, the nozzle throat erosion is mainly diffusion controlled. This observation stresses the importance of more accurate and definitive kinetic parameters for graphite oxidation reactions, especially at lower pressures. It was also observed that, besides H 2 O, the OH species affects the nozzle recession rate greatly. For the metallized propellant, the concentrations of major oxidizing species such as H 2 O, OH, and CO 2 are substantially reduced in comparison with the nonmetallized propellant, resulting in significant reduction of the erosion rates. A comparison of experimental data and predicted results from the graphite nozzle erosion minimization code shows excellent agreement especially for the nonmetallized propellant. To substantially reduce the throat recession rates at high pressures, it is suggested that the boundary-layer control at the throat region could be an effective method for future nozzle design considerations.