The X2 facility at the University of Queensland was modified to allow experimentation at low pressures in a nonreflected shock tube mode. Titan conditions (98% N2, 2% CH4) were examined. Emission spectroscopy measurements were taken for three conditions, with freestream pressures of 13, 8, and 4 Pa, and average shock speeds of 6.4, 6.2, and 9.0 km/s, respectively. A region approximately 100mmlong was imaged onto the entrance slit of the spectrometer. Comparisons with previous experimental work showed that the peak nonequilibrium emission intensity behind the shock was consistent for the 13 and 8 Pa conditions. The spectral results showed that, in comparison to these previous results, the modified facility resulted in significant improvements in signal strength and an increase in the length of test flow available at such low-pressure conditions, allowing finer spectral resolution and the potential, if needed, for further spatial resolution. The experimental results at the 4 Pa condition were the first results obtained at such a low pressure. They provided information about the nonequilibrium peak and falloff rate of the radiative heating behind the shock wave. The results showed consistency and repeatability, and sufficient test time and test gas were available to allow the capture of high-resolution spectral images, even at the lowest pressure condition.
Journal of Thermophysics and Heat Transfer / Vol. 29, No. 4, pp.835-844