Steady State Simulation of Pyrolysis Gases in an Inductively Coupled Plasma Facility
Abstract
An important step in the more efficient use of PICA (Phenolic Impregnated Carbon Ablator) as a Thermal Protection System (TPS) material for spacecraft is the understanding of its pyrolysis mechanics. The gases released during pyrolysis and their subsequent interaction with the reactive plasma environment is not yet well understood. The surface recession of PICA as it ablates during testing only makes the study and characterization of the chemical reactions more difficult. To this end, a probe has been designed for this study to simulate, in steady state, the pyrolysis gases within the UVM 30kW Inductively Coupled Plasma (ICP) Torch Facility. This probe, which is an extension of previous work done at UVM, has been used to inject Carbon Dioxide, Hydrogen, and a mixture of the two into pure Argon and dilute Nitrogen, Oxygen, and air plasmas. During testing, spatially resolved, pointwise, line of sight emission measurements were taken in the boundary layer region. These results were then compared to temporally resolved PICA emission data taken in a previous study. After the correct temporal PICA scan was found the data sets closely matched. This indicates that the gas-injection probe is a viable method to simulate pyrolysis in a steady state environment. The key pyrolysis species of CN, NH, OH, Hydrogen Alpha (Hα), and Hydrogen Beta (Hβ) were spatially traced along the stagnation line for the pure Hydrogen and mixture injection cases. These measurements show evidence of spatial relationships between NH and Hα as well as between OH and Hβ. They also show that all of the molecules tend to follow the same general trend spatially. The work done for this study has both reintegrated gas-injection capability into the UVM facility as well as laid the groundwork for future gas-injection testing within the facility. Spatial emission analysis techniques currently being developed at UVM will provide a more resolved picture of the interactions occurring in the boundary layer once completed.