Thermochemical Erosion Analysis for Graphite/Carbon-Carbon Rocket Nozzles

A study is conducted to predict graphite/carbon carbon nozzle erosion behavior in solid rocket motors for wide variations of propellant formulations. The numerical model considers the solution of Reynolds-averaged Navier-Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, variable transport and thermodynamic properties, and heat conduction in the nozzle material. Two different ablation models are considered and compared: a surface equilibrium approach and a finite-rate model. Results show that the erosion rate is diffusion limited for metallized propellants, ensuring sufficiently high wall temperatures, and it is kinetic limited for nonmetallized propellants. For low surface temperatures, the two models are consistent with each other and predict the same erosion rate, while the surface equilibrium model overpredicts the recession at low surface temperatures. The calculated results show an excellent agreement with the experimental data from the ballistic test and evaluation system motor firings, and the finite-rate model actually improves the predictions when the kinetic-limited regime is approached.