Scramjet Inflow Characterization Based on Thermodynamic Analysis of Arc-Heater Plenum

The inflow conditions of the working gas in the ACT-II facility are characterized using tunable diode laser absorption spectroscopy (TDLAS). The ACT-II facility at the University of Illinois at Urbana-Champaign, an arc-heated supersonic combustion tunnel, is used as a ground test platform to explore the combustion dynamics in a scramjet flowpath. The temperatures achieved through the arc-heater introduce dissociation of the working gas and subsequent production of species such as nitric oxide (NO). Presence of NO has been shown to influence combustion performance, specifically as a reduction in ignition delay, and as such is critical to quantify in order to accurately predict flight performance from ground test results. A NO sensor is designed to measure NO mole fraction and temperature in the plenum, downstream of the arc-heater, to characterize the working gas in the facility. The experiments are performed targeting a carefully selected mid-infrared absorption feature to ensure good temperature sensitivity and low concentration detection limit. Tests are performed at three different pressure conditions at a 50 Hz sampling rate. These results would provide inflow conditions to computational models simulating similar conditions, and allow more accurate comparisons between the modeled predictions and the ACT-II experiments.