ИСТИНА

Nowadays there is a fast growing interest in application of non-equilibrium plasma for the plasma-assisted combustion. Excited molecules produced in non-equilibrium plasma influence on combustion - decreasing the ignition temperature and the induction delay time and increasing the flame velocity [1]. Low-lying electronically excited states of the oxygen molecule O2(1Δg) and O2(1Σg) attract special attention [2]. However, still there is a great lack of knowledge on the reactions of hydrogen radicals (especially H and HO2) with O2(1Δg) that hamper the development of adequate kinetic schemes for needs of plasma-assisted combustion and atmospheric chemistry. In this paper, we analyzed currently existing approaches to the description of reactions of O2(1Δg) with both H and HO2, and the variation of the rate constants of these reactions. We carried out the simulations of a hydrogen-oxygen mixture with O2(1Δg) in a wide range of gas temperatures: 300 K - 1020 K on the basis of experimental data obtained in one experiment [3]. In this experiment using a combined discharge flow/shock apparatus the effective rate constant of O2(1Δg) deactivation was obtained by measuring the changes of dimol emission intensity in the excited (in discharge) oxygen flow with small admixtures of H2. Our calculations at the experimental conditions were performed using two-dimensional gas dynamics model [4] and zero-dimensional kinetic model for parametric studies. The reaction kinetics included 10 reactive species H2, O2, H, O, OH, H2O, HO2, H2O2, O3 and O2(1Δg) and 46 reversed chemical reactions. The analysis of existing data in the literature on kinetic processes in H2-O2-O2(1Δg) mixture, affecting the O2(1Δg) quenching under considered conditions were carried out. It was shown that the main role in the deactivation of O2(1Δg) at 300 - 700 K is played by processes involving the radical HO2 and also depends on residual fraction of atomic oxygen (from discharge) in the gas stream. The uncertainties in the rate constants of the reactions O2(1Δg)+HO2↔O2+HO2* (R1), HO2*+O2(1Δg)→H+O2+O2 (R2) were analysed and their range of variation were determined assuming both high and low rate (in compare with rate of reaction (R-1)) of HO2* quenching in HO2*+M→HO2+M. At temperatures above 850 K, the O2(1Δg) quenching is entirely due to the reaction H+O2(1Δg)→products. But for consistency with the experimental data [3] the rate constant of this process should be considerably reduced (by an order). This result contradicts with direct measurement of the rate constant of this reaction and its theoretical estimations (mentioned in [4]). This indicates that there are certain mechanism reducing the effective rate of O2(1Δg) quenching at high temperatures that are not included in the current models of H2-O2-O2(1Δg) kinetics. Apparently, such a complex mechanism should simultaneously include both the process restoring of the O2(1Δg), and the process that decreases the atomic hydrogen concentration in the presence of O2(1Δg). References: [1] Starikovskaia S.M.,// J. Phys. D: Appl. Phys. 2006, 39, R265–R299. [2] Popov N.A.,// AIAA 2012-2989, 43rd AIAA Plasmadynamics and Lasers Conference 25 - 28 June 2012, New Orleans, Louisiana. [3] Borrell P., Richards D.S. // J. Chem. Soc. Faraday Trans. II. 1989. V 85. P. 1401-1411. [4] Chukalovsky A.A., et.al.,// Combustion Science and Technology. 2012. V. 184. № 10-11. P. 1768-1786.