Effect of nozzle thermal environment on the ablation rate of the throat inserts of solid rocket motors

Solid rocket motors using five different C/C composites (radially woven 4D C/C, axially woven 4D C/C, integral felt C/C, needle felt C/C and punctured 3D C/C) and two kinds of graphite (T705 graphite and an anisotropic pyrolytic graphite with a density of 2.18 g/cm³, a porosity of 1% and graphene layers perpendicular to throat surface) as the throat inserts were propelled by hydroxyl terminated polybutadiene or a high energy fuel to test the ablation rates of the throat inserts. The effect of nozzle thermal environment (propellant type and combustion chamber pressure) on the ablation rates of the throat insert materials was investigated under identical conditions. Results show that the ablation rates of the carbon materials are closely related to the concentration of the oxidative gases (H₂O and CO₂) and the chamber pressure. The chamber pressure is of primary importance, and doubling it leads to an increase of ablation rates by 1.8-2.6 times. The ablation rates using the hydroxyl terminated polybutadiene propellant are 51.6%-65.1% higher than those using the high energy propellant because the concentration of oxidizing H₂O in the former is 1.26 times higher than that in the latter. The pyrolytic graphite has the lowest ablation rate followed by the integral felt C/C, needle felt C/C and axially woven 4D C/C. The radially woven 4D C/C has the highest rate, and the punctured 3D C/C and T705 graphite have similar ablation rates. The ablation rates of the five composites and two graphites made in China are similar or superior to the C/C composites and Graphnol graphite made in other countries.