Numerical and Experimental Investigation of Motor Pressure Effect on Thermochemical Erosion of Graphite Nozzle in Solid Fuel Engines

Abstract

Using heat shield, especially in throat area has a significant effect on combustion chamber pressure and thermal efficiency of solid fuel engines. Precise prediction of the regression of throat area for different pressures, will lead to optimal design of the motors, specifically for those of long burnout times. In this work, erosion of graphite nozzles employed in solid propellant motors with a specific composite propellant and variable pressures, is investigated. The numerical model utilized includes the Naiver-Stokes equations, chamber gas thermodynamic equations and thermochemical and heat conduction equations for the nozzle surface. In order to validate the numerical results, a cartridge type solid propellant motor with a graphite nozzle is experimentally tested. Using a 3D scanner in the experimental setup, the amount of inner surface regression for variable pressures (60, 90, 120 and 200 bars) is measured. Numerical and experimental results are in a proper conformity with each other. There is a direct relationship between convection heat transfer coefficient and the pressure. The overall erosion is the same for all four engine pressures. The erosion rate increases with increasing pressure. This rate for the fuel is about 0.21 mm/s for every 100 times the pressure up to 300 times. For a pressure higher than 300 times, a significant leakage occurs at the corrosion rate.