CO concentration measurements using tunable diode laser absorption spectroscopy behind the shock waves in Martian atmosphere

摘要

Shock tube experiments are carried out to study the physical and chemical processes during a vehicle entry into the Marsatmosphere using tunable diode laser absorption spectroscopy (TDLAS) and optical emission spectroscopy (OES). COconcentration distributions are diagnosed behind a shock wave in a CO_2-N_2 mixture with three different conditions ofinitial pressure and velocity. The strong shock wave is established in a shock tube driven by combustion of hydrogen andoxygen. Time-resolved spectra of the Δv = 0 sequence of the B~2Σ~+→X~2Σ~+ electronic transition of CN have been observedthrough OES. A precise analysis of the CN violet spectra is performed and used to determine rotational and vibrationaltemperatures. Two absorption lines in the first overtone band of CO near 2.33 μm, are selected from a HITRANsimulation to calibrate laser wavelength and detect the CO concentration. Combined with these temperature results usingOES, CO concentrations in the thermal equilibrium region are derived, which are 2.91 × 10~(17) cm~(-3), 7.46 × 10~(17) cm~(-3) and1.01 × 10~(18) cm~(-3), corresponding to equilibrium temperatures equal to 7000 ± 400 K, 7400 ± 300 K, 6000 ± 300 K in thelow, medium and high pressure conditions, respectively.