Modeling of Emission Spectra in Nonequilibrium Plasmas for Testing Pyrolyzing Ablators

Simulations are performed in collaboration with inductively coupled plasma torch experiments to investigate gas-phase chemical kinetics in the boundary layer of a pyrolyzing ablator. A gas injection probe delivers CO2 or H2 into plasma mixtures of Ar/N2/O2, and emission spectroscopy provides absolute, spatially, and spectrally resolved measurements of the radiative emission in the boundary layer. A computational model of the plasma flow in the Inductively Coupled Plasma facility was used with finite rate chemistry mechanisms, and line-of-sight emission spectra were computed from the results to assess the accuracy of the chemistry mechanisms. The CO2-air and H2-air chemistries were examined, and CN emission levels were overpredicted by a factor of 3-4, whereas OH emission was underpredicted by a factor of 2. Sensitivity analyses show that uncertainty in the experimental temperature accounts for much of the discrepancy.