Chemical Erosion of Refractory-Metal Nozzle Inserts in Solid-Propellant Rocket Motors

摘要

An integrated theoreticalumerical framework is established and validated to study the chemical erosion ofnrefractory-metal (tungsten, rhenium, and molybdenum) nozzle inserts in solid-rocket-motor environments, with anprimary focus on tungsten. The formulation takes into account multicomponent thermofluid dynamics in the gasnphase, heterogeneous reactions at the surface, energy transport in the solid phase, and nozzle material properties.nTypical combustion species of nonmetallized ammonium-perchlorate/hydroxyl-terminated-polybutadienenpropellants at practical motor operating conditions are considered. The erosion rates calculated by employingnthree different sets of chemical kinetics data available in the literature for the tungsten-steam reaction have beenncompared. The effect of considering either of two different tungsten oxides, WO2 or WO3, as the final product ofnsurface reactions is also investigated. The predicted erosion rates compare well with experimental data. Thenoxidizing species of H2O proved more detrimental than CO2 in dictating the tungsten nozzle erosion. The materialnrecession rate is controlled by heterogeneous chemical kinetics because the diffusion limit is not reached. The erosionnrate increases with increasing chamber pressure, mainly due to higher convective heat transfer and enhancednheterogeneous surface reactions. The tungsten nozzle erodes much more slowly than graphite, but at a ratencomparable with that of rhenium. The molybdenum nozzle exhibits the least erosion for flame temperatures lowernthan 2860 K. Its low melting temperature (2896 K), however, restricts applications for propellants with high flamentemperatures.