The performance deterioration of solid-rocket motors caused by nozzle throat erosion becomes more severe with increased operating pressure from higher rates of heat and mass transfer from the core flow to the nozzle surface. Understanding of the rocket nozzle throat erosion processes and developing methods for mitigation of erosion rate can allow motor operation pressures to be substantially higher than those of the existing propulsion systems. Two test rigs have been utilized in the study of nozzle throat erosion phenomena for G-90 grade graphite; an instrumented solid propellant motor (ISPM) and a solid-propellant rocket motor simulator (RMS). The X-ray translucent nozzle assembly used for the RMS and ISPM allows the real-time imaging of the nozzle-throat station.
It also has the feature for incorporating a nozzle boundary-layer control system (NBLCS) to mitigate nozzle-throat erosion rates. The RMS is a gaseous reactant combustor, allows for control of product species compositions, their flow rates, and combustor operating pressure. The erosion process of G-90 graphite was also evaluated in the ISPM using both non-metallized and metallized composite solid propellants. Tests conducted at operating pressures around 21 MPa showed greatly reduced nozzle throat erosion rate when the NBLCS was utilized. A dimensionless nozzle-throat erosion rate correlation was developed in terms of the effective oxidizer mass fraction, chamber pressure, Reynolds number, and relative boundary layer thickness. The correlation equation accurately predicts erosion rate data measured in the RMS and the ISPM for both non-metallized and metallized propellants over a wide range of operating conditions. The calculated erosion rates from the correlation showed agreement within ± 0.05 mm/s of the experimentally determined values.