Nonequilibrium and equilibrium shock front radiation measurements

Abstract

The intensities of the radiation emitted behind a normal shock wave in nitrogen were measured in an electric-arc driven shock tube, at a shock velocity of 6.2 km/s. Both a time-resolved broadband radiation intensity measurement and a time-frozen spectral measurement were conducted. The time-frozen measurement was made by a 0.3-m spectrograph equipped with a 700-element linear diode array at the exit focal plane, which gave a spectral resolution of 0.3Å per element. By analyzing the second positive system of N2 in the 3153-3159-A wavelength region, the rotational and vibrational temperatures are determined in both the equilibrium and the nonequilibrium regions. The results are compared with similar data obtained by the AVCO-Everett Research Laboratory during the 1960s. The relaxation times and the temperature in the equilibrium region obtained in the present experiment agree with those of AVCO, but the vibrational and rotational temperatures in the nonequilibrium region are greatly different from the AVCO results. The measured rotational temperature seems to be in nonequilibrium, contradicting the two-temperature assumption of Park, but the measured vibrational temperature agrees with Park's model.