Combined TDLAS and OES technique for CO concentration measurement in shock-heated Martian atmosphere

Abstract

This paper describes the CO concentration and gas temperature distribution measurements behind a strong shock wave in the simulated Martian atmosphere by an optical diagnostic system. The strong shock wave (6.31 ± 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. The optical diagnostic system consists of two parts: the optical emission spectroscopy (OES) system and the tunable diode laser absorption spectroscopy (TDLAS) system. For OES system, high temporal and spatial resolution experimental spectra of CN violet system (B 2 Σ + →X 2 Σ + , Δv = 0 sequence) have been observed. Rotational and vibrational temperature distribution along the shock wave is inferred through a precise analysis of high-resolution experimental spectra. For TDLAS system, a CO absorption line near 2335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode. Combined with these experimental results using OES, CO concentration in the thermal equilibrium region is derived. The detected average CO concentration is 7.46 × 10 12 cm -3 with the average temperature of 7400 K ± 300 K, which corresponds to the center fractional absorption of 2.7%.

A new flux splitting scheme for Euler equations of gas dynamics

“…However, many questions remain on the physical and chemical models, especially on the mechanisms of thermochemical relaxation and chemical reaction [14][15][16] . During high-speed entry into Mars atmosphere, the dissociation of CO 2 is one of the most important reactions because it is the first chemical reaction to occur behind a shock wave and it affects the whole chemical reactions 17,18 . Temperature is another crucial thermodynamic quantity in shock-induced chemistry, especially the rotational temperature, which controls the collision probability of the gaseous particles in a chemically reacting hot gas [19][20][21] .…”