Nonintrusive Nitric Oxide Density Measurements in the NASA Langley Arc- Heated Scramjet Engine Test Facility

Abstract : A nitric oxide (NO) resonance absorption technique was used to determine average path integrated NO number densities through the expanded flow of the NASA Langley Arc-Heated Scramjet Test Facility. The mole fraction ranged from 0.016 to 0.019 (with a 20-percent uncertainty) for static temperatures from 186 to 320 K. Absorption was observed in the NO gamma (0,1) band that could not be accounted for at the static flow conditions if the NO were at vibrational equilibrium. Using the (0,1) transmittance measurement and the number density calculated from the (0,0) transmittance measurement, vibrational temperatures ranging from 534 to 919 K were calculated with a minimum uncertainty from - 15 to 21 percent. A nonequilibrium vibrational temperature, 1,100 K, was calculated from a one-dimensional kinetic (ODK) chemistry code compared to the 919 K determine from the measurement. Within the range of uncertainties of the (0,1) absorption measurements, the corresponding NO radiative transfer code calculations of vibrational temperature, and the range of uncertainties of the ODK code calculations, there is good agreement in the resulting vibrational temperatures.