O. P. Shatalov

Investigation of oxygen dissociation and vibrational relaxation at temperatures 4000–10 800 K

The oxygen absorbance was studied at wavelengths 200-270 nm in Schumann-Runge system behind the front of a strong shock wave. Using these data, the vibrational temperature Tv behind the front of shock waves was measured at temperatures 4000-10,800 K in undiluted oxygen. Determination of Tv was based on the measurements of time histories of absorbance for two wavelengths behind the shock front and on the results of detail calculations of oxygen absorption spectrum. Solving the system of standard quasi-one-dimensional gas dynamics equations and using the measured vibrational temperature, the time evolution of oxygen concentration and other gas parameters in each experiment were calculated. Based on these data, the oxygen dissociation rate constants were obtained for thermal equilibrium and thermal non-equilibrium conditions. Furthermore, the oxygen vibrational relaxation time was also determined at high temperatures. Using the experimental data, various theoretical and empirical models of high-temperature dissociation were tested, including the empirical model proposed in the present work.

Numerical simulation of ignition of a hydrogen-oxygen mixture in view of electronically excited components

Results are given of numerical simulation of the kinetics of ignition of a stoichiometric hydrogenoxygen mixture diluted with argon behind the front of an incident shock wave. The simulation involves the use of a data base for rate constants of chemical reactions, which includes processes in view of electronically excited components OH*(2Σ+), O*(1D), and O*2(1Δ). The calculated values of time required to reach the maximum of intensity of radiation of excited OH* radical at wavelength λ = 306.4 nm are in adequate agreement with the experimentally measured values. The contributions made by various reactions to the production of components of the gas ixture are determined.

Dissociation rate constants of diatomic molecules under thermal equilibrium conditions

By means of an analysis of currently available experimental data and theoretical models, expressions for the dissociation rate constantk0 are obtained for thermal equilibrium conditions. These expressions are necessary for describing the molecular dissociation process under both thermal equilibrium and non-equilibrium conditions in the gas.k0 values are presented for the O2, N2, NO, CO, CN, and C2 molecules at temperatures from 300 to 40,000 K, and their errors are estimated.

Dissociation rate constants for oxygen at temperatures up to 11000 K

Measurements of the absorption and vibrational temperature evolution of molecular oxygen behind the shock wave front in regimes with temperatures near the front varying over the range 4000–11 000 K made it possible to determine the dissociation rate constant for O2 molecules under both thermal equilibrium and nonequilibrium conditions. The dependence of the dissociation rate constant on the ratio Tv/T, that is, on the deviation from the thermal equilibrium conditions, is demonstrated experimentally. The corresponding expression for the two-temperature dissociation rate constant is proposed.

Nonequilibrium Spectral Radiation Behind the Shock Waves in Martian and Earth Atmospheres

Paper presents the review of experimental data on the measurements of radiative characteristics of shock waves as well as comparison of measurements of nonequilibrium spectral radiation of shock-heated N2-O2 and CO2-N2 gas mixtures with the results of numerical simulations. The experimental results on the absolute measurements of nonequilibrium spectral radiation were obtained on the shock tubes of Laboratory of Kinetic Process in Gases of Institute of Mechanics MSU. The numerical nonequilibrium spectral features of the shock-heated gases in absolute units were obtained using the model of nonequilibrium radiation emitted in the relaxation zone.

Measurement of the vibrational temperature of oxygen behind a shock wave front under thermal and chemical nonequilibrium conditions

In shock tube experiments the profiles of light absorption in oxygen are obtained for the wavelength interval 200–260 nm over the temperature range 4000–10800 K. Using these data, the vibrational temperature profiles are measured for oxygen molecules behind the shock front. The method of determination of the vibrational temperature of oxygen is based on comparing absorption measurements and detailed absorption spectrum calculations for oxygen in the Schumann-Runge system.

Nonequilibrium radiation behind the strong shock waves in marsian and titan atmospheres: Numerical rebuilding of experimental data

The computati onal model of nonequili brium radi ation emitted in the relaxati on zone behind shock front is presented in the paper. The hydrodynamic description of relaxati on zone is performed in the framework of Euler equations. The model includes different physical chemical processes such as chemical kinetics, relaxati on of vi brational energy. Also the equation for the determinati on of electron gas temperature is solved. The “justoverl appi ng” line model is used for the calculation of the s pectral emissivity. The presented model is used in order to obtain vari ous characteristics of radiation (spectral emissivity, spatial distri buti on of s pectral emissivity integrated over s pecific wavelength region, maxi mum val ue of the nonequili brium radi ation) behind shock front for the conditi ons which are relevant to the experi mental data obtained on different facilities. Comparison of experi mental and theoretical data is presented in the paper. The reasons for the discrepancies are discussed.

Measuring the ignition delay time for hydrogen-oxygen mixtures behind the front of an incident shock wave

The delay time τ has been measured for the formation of the ·OH radical in igniting hydrogenoxygen mixtures diluted with argon (79–97%). The experiments have been carried out under incident shock wave conditions at temperatures of 900–3000 K, pressures of 0.5–2.5 atm, and H2/O2 ratios of 0.2–20. The dependence of τ on the pressure Ps of the stoichiometric part of the combustible mixture (2H2-O2) has been investigated for different mixture compositions. Under the above conditions, τ depends practically linearly on 1/Ps at Ps = 0.02−0.1 atm, irrespective of the mixture composition. This allows the measured τ data to be converted to one quantity, τPs. The temperature dependence of τPs in the Ps range from 0.02 to 0.1 atm is Arrhenius-like. For the hydrogen-rich mixtures (H2/O2 = 2–20), this dependence appears as τPs= 0.057 + 0.0256exp(7470/T) μs atm; for the lean mixtures (H2/O2 = 0.125–1), τPs = 0.021 + 0.0069exp(7470/T) μs atm. The length of the shock-heated gas plug in the incident shock wave poses limitations on the ignition delay time measurements at T < 900 K.

Equilibrium and non-equilibrium rate constants of oxygen dissociation at high temperatures

Basing on the measurement of oxygen vibrational temperature behind the front of a strong shock wave, the parameters of high-temperature gas flow were calculated. The oxygen dissociation rate constants were obtained for thermal equilibrium conditions as well as for thermal non-equilibrium ones. The expression for the thermal equilibrium dissociation rate constant was obtained at temperatures near the front 6000-11000K. The simulation of high-temperature oxygen flow behind the front of the shock wave was performed in quasi-one-dimensional approximation. The empirical model of high-temperature dissociation is proposed for the description of the temperature evolution behind the front of shock wave, and the calculated profiles of vibrational and translational temperatures were compared with the measured ones.

Study of the absorption characteristics of molecular oxygen in the Schumann-Runge system at high temperatures: II. Experiment and comparison with calculation

Absorption cross sections of oxygen molecules in the UV spectral range are experimentally determined in the temperature range 1600–6000 K. The absorption cross sections are measured in oxygen or in its mixtures with argon behind the shock wave front. Measurements are performed for the spectral range 190–270 nm, which pertains to the electronic transition X3Σg− → B3Σu− of the Schumann-Runge system. The absorption cross sections are also measured at temperatures 291 and 3300 K in the range 160–185 nm. The measured absorption cross sections are compared with the calculated spectra of the O2 molecule.