Flow Characterization of CO₂-N₂-Ar Plasma in a Hollow Electrode Arc Heater

Abstract

The purpose of the present study is to characterize the flow of CO2-N2-Ar plasma in a hollow electrode arc heater using optical diagnostics. Spectroscopic measurements are conducted in the region of the arc-heated part. The rotational and vibrational temperatures are determined from the measured spectra of CN Violet ∆v=0 and C2 Swan ∆v=0 using a spectrum fitting technique. It is found that the rotational and vibrational temperatures are almost same, showing that the plasma in the arc heater is close to thermal equilibrium. The chemical composition of the plasma is calculated using the NASA-CEA program. The result shows that Ar, CO, and O are dominant species in the plasma investigated in this study. Although the mole fractions of CN and C2 are extremely low, they are strong radiators in the CO2-N2-Ar plasma. The numerical spectrum in the wide wavelength range is calculated using the chemical composition deduced by the NASA-CEA program and compared with the measured one. The result shows that the numerical spectrum does not agree with the measured one due to contamination caused by carbon. Spectrum calculations are conducted parametrically by changing the chemical composition to investigate the influence of carbon contamination. The numerical spectrum becomes close to the measured one when the mole fractions of CN and C2 decrease, showing that carbon contamination has a significant influence on the reaction processes of the plasma in the arc heater.