Measurements of non-equilibrium and equilibrium temperature behind a strong shock wave in simulated martian atmosphere

Abstract

Non-equilibrium radiation measurements behind strong shock wave for simulated Martian atmosphere are presented in this paper. The shock wave is established in a hydrogen oxygen combustion driven shock tube. Timeresolved spectra of the Δv = 0 sequence of the B 2 Σ + → X 2 Σ + electronic transition of CN have been observed through optical emission spectroscopy (OES). A new method, which is based on fitting high resolution spectrum for rotational and vibrational temperatures measurement, is proposed to diagnose temperature distribution behind the shock wave. It is estimated that the current scheme has the maximum deviation less than 8% (1σ) for vibrational temperature measurement through detailed analysis of the influence of the uncertainties of spectroscopic constants and spectral resolution. Radiation structure of the shock layer, including induction, relaxation and equilibrium process, and corresponding rotational and vibrational temperatures are obtained through time gating OES diagnostics with sub-microsecond temporal resolution. The present extensive results will strongly benefit the reaction rate estimation and computational fluid dynamics (CFD) code validation in high enthalpy Mars reentry chemistry.

Experimental and modeling investigation of CO2 dissociation in Mars entry condition

“…In our previous studies, the spectral structure of CN violet system has been investigated and a theoretical synthetic spectrum has been calculated based on our spectral resolution [12]. The rotational temperature can be determined by comparing the range (385 nm -390 nm) of the CN violet system between the experimental and theoretical spectra.…”

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

“…The temperature distribution along shock profile can be directly obtained through a precise analysis of high-resolution experimental spectra. The processing method is detailed described in the literature 11 . The TDLAS system is operated in scanned-wavelength direct absorption mode to diagnose one CO absorption line near 2335.778 nm.…”

“…In our experiments, the absorption length is fixed at 7.8 cm, pressure after the strong shock wave is about 1.1 atm by thermodynamic calculations, and temperature in the thermal equilibrium region behind the strong shock wave is 7400 ± 300 K by optical emission spectroscopy 11 . Absorption spectra based on the HITRAN2008 database near 2.3 μm are computed for choosing appropriate CO transitions, as shown in Figure 1.…”

“…According to the measured spectral resolution, rotational temperature can be directly obtained through a precise analysis between an experimental spectrum and theoretical spectrum in this wavelength range. More details and error analysis description of this method are given in the literature 11 . Then the vibrational temperature is estimated by minimizing the difference between the experimental and theoretical spectrum.…”

A new flux splitting scheme for Euler equations of gas dynamics

“…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] . Therefore, accurate quantitative measurement of the number density of carbon monoxide and temperature after the strong shock wave will help to study carbon dioxide dissociation and validation the relevant chemical kinetic models.…”