Investigating Arcjet Mixing and Enthalpy Loss Using Atomic Oxygen Laser Absorption Spectroscopy

Abstract

Scanned-direct absorption spectroscopy was implemented to improve sensing capabilities in the mixing volume (MV) of the 60 MW Interaction Heating Facility (IHF) at NASA Ames Research Center. The IHF MV conditions range from 5000 to 8000 K and 1 to 9 atm. The path-average line-of-sight measurements of the temperature and enthalpy were inferred using an electronic atomic oxygen transition near 777 nm. A scanned-DAS sensor was optimized to capture high-add-air and high-pressure conditions that previously had not been measurable, including an increased tuning range () that allowed for full absorbance profile resolution at maximum pressure test conditions. Enhanced sensor capabilities confirmed uniform flow and flat temperature profiles immediately upstream of the arcjet’s converging–diverging nozzle inlet. Less uniform and parabolic temperature profiles were observed immediately downstream of add-air injection. Time-resolved enthalpy measurements ranged from 16 to 27 MJ/kg and are in agreement with the IHF’s current measurement methods. Centerline measurements along the MV confirmed a reduction in achievable enthalpy after installation of the MV. The centerline measurements quantified the mixing process for various add-air conditions, indicating an opportunity for enthalpy recapture. Axial locations of sufficient mixing were identified and provide a potential for reduction of the MV length and improved facility performance.