RECESSION OF GRAPHITIC NOZZLES IN ROCKET MOTORS

A study has been conducted to develop a capability to predict recession of graphitic nozzles in rocket motors. Both theoretical and experimental studies were undertaken. In the theoretical investigation, a model was developed based on the aerothermochemistry of the recession process. The problem was modeled as a quasi-steady, turbulent boundary-layer flow coupled through boundary conditions to the transient heat conduction process in the nozzle material. In the experimental investigation, a test rig has been designed and constructed to study the recession phenomenon of two different nozzle materials under identical flow conditions. Attempts to film the recession process were not successful since no transparent window material could withstand the high temperatures of the combustion products of aluminized propellants.; The theoretical model was used to predict recession and heat transfer in different motors, for different nozzle geometries and materials, at different operating pressures and temperatures, and wide range of propellant formulations. There is agreement between the theoretical predictions and the experimental data. Recession is found to be strongly influenced by such parameters as propellant composition, chamber pressure, and motor geometry.; The results of this study affirm that recession occurs primarily due to the oxidation of carbon to carbon monoxide. The most important oxidizing species are H(,2)O and CO(,2). Results show that the influence of chemical kinetics is predominant only in the short initial phase when surface temperatures are low. After nozzle surface temperatures have reached about 2500 K, the recession rate is then largely determined by the diffusion rate of oxidizing species.