Experimental investigation of non-equilibrium spectra for nitrogen behind strong shock waves

The non-equilibrium spectra of shock-heated nitrogen in the UV-visible range are investigated in a detonation driven shock tube. Spectral identification indicates that the main contributors to the spectra are molecular radiation of N2(2+) and N+2(1-). Vibrational and rotational temperatures of N2(C) and N+2(B) are determined through spectral fitting. The post-shock spectra of pure nitrogen are obtained for shock velocities ranging from 6.82-9.00 km/s and P0 = 30-200 Pa at the shock arrival time. Differences between vibrational and rotational temperatures of N2(C) and N+2(B) are observed, suggesting that nitrogen is in a non-equilibrium state at shock arrival moment. Time-resolved spectra are obtained within varying delay times of 0-2.0 mu s at P0 = 200 Pa and shock velocity of Vsw = 6.60 km/s. Time-resolved temperatures are determined to illustrate the time-resolved non-equilibrium characteristics of nitrogen at high temperature. It is observed that the non equilibrium characteristics of nitrogen gradually weaken with increasing time and the thermal equilibrium was not obtained within 2.0 mu s. Finally, the time-resolved temperatures are compared with CEA (Chemical Equilibrium with Applications) prediction, revealing that the difference in temperature between the experiment and the CEA equilibrium calculation decreases as time increases.