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Uhl, J.

Mechanical Engineering

2012

MS

In this study the pyrolysis process of a phenolic impregnated-carbon ablator (PICA) is investigated. PICA is an ablative heat shield material that is now being implemented for high speed vehicle entry missions. The material is performant owing to its pyrolysing characteristics at elevated temperatures, which augments convective blockage to reduce heat transferred to the vehicle. However the gas phase interactions in the near surface region between the plasma flow and the pyrolysis gases have not been fully investigated. This study provides information about the impact of the pyrolysis of PICA on the near-wall thermochemistry, the surface recession, the mass loss over time and the flow pattern at the stagnation point by testing virgin PICA material and its nonimpregnated fiberform substrate in various plasma conditions. A parallel investigation of the pyrolysis gas flow dynamics is also reported using a simulation probe. The probe is designed with the ability to inject a gas into the oncoming plasma flow through a porous graphite plug to mimic the release of gas through the charred layer of an actual ablator. Tests are performed in pure N2, air and C02 plasma flows and emission spectroscopic measurements are used to obtain information on the chemical state of the pyrolysis and plasma gas mixtures. All experiments are conducted in the 30 kW Inductively Coupled Plasma (ICP) Torch Facility at the University of Vermont.