Temperature and Enthalpy Characterization of NASA Arcjet Using Oxygen and Nitrogen Absorption

We report on measurements of temperature and enthalpy in the 60-MW Interaction Heating Facility (IHF) Arcjet at the NASA Ames Research Center using tunable diode laser absorption spectroscopy. Measurements were made in the add-air plenum of the IHF, positioned between the downstream electrodes and the nozzle, which serves as the reservoir condition for the ensuing supersonic expansion. Spectroscopic measurements of atomic oxygen (O), atomic nitrogen (N), and molecular nitrogen ([Formula: see text]) serve as the basis for the reservoir characterization. Data was collected at four nominal IHF conditions spanning 11 different locations within the plenum. Measurements suggest greater radial flow uniformity at the end of the plenum than at the beginning, but at the price of flow enthalpy in the core. Agreement between separately inferred oxygen and nitrogen temperatures was variable between different conditions in the range of 1–5%. The IHF routinely demonstrates a high degree of stability in measured parameters over many minutes, but large fluctuations on the order of 500 K on millisecond timescales are noted and discussed. Inferred enthalpy profiles are compared with CFD predictions for two IHF conditions. Proposed bulk enthalpies from measurements are found to be lower by [Formula: see text], while normalized enthalpy profiles agree within 3%.