Abstract
A kinetic scheme for non-equilibrium regimes of atmospheric pressure air discharges is developed. A distinctive feature of this model is that it includes associative ionization with the participation of N(2D, 2P) atoms. The thermal dissociation of vibrationally excited nitrogen molecules and the electronic excitation from all the vibrational levels of the nitrogen molecules are also accounted for. The model is used to simulate the parameters of a glow discharge ignited in a fast longitudinal flow of preheated (T0 = 1800–2900 K) air. The results adequately describe the dependence of the electric field in the glow discharge on the initial gas temperature. For T0 = 1800 K, a substantial acceleration in the ionization kinetics of the discharge is found at current densities larger than 3 A/cm2, mainly due to the N(2P) + O(3P) → NO+ + e process; being the N(2P) atoms produced via quenching of N2(A3∑u+) molecules by N(4S) atoms. Correspondingly, the reduced electric field noticeably falls because the electron energy (6.2 eV) required for the excitation of the N2(A3∑u+) state is considerably lower than the ionization energy (9.27 eV) of the NO molecules. For higher values of T0, the associative ionization N(2D) + O(3P) → NO+ + e process (with a low–activation barrier of 0.38 eV) becomes also important in the production of charged particles. The N(2D) atoms being mainly produced via quenching of N2(A3∑u+) molecules by O(3P) atoms.
Highlights
A number of experiments have been reported on non-equilibrium regimes of discharges in atmospheric-pressure air, in particular, glow-type discharges in open ambient air (e.g., [1,2,3,4,5,6,7,8,9,10,11,12]), and in fast longitudinal flows of air [13,14]
The reduced electric field noticeably falls because the electron energy (6.2 eV) required for the excitation of the N2 (A3 u + ) state is considerably lower than the ionization energy (9.27 eV) of the NO molecules
The discharge is ignited between two needle electrodes oriented along the axis of the gas flow directed from the cathode to the anode
Summary
A number of experiments have been reported on non-equilibrium regimes of discharges in atmospheric-pressure air, in particular, glow-type discharges in open ambient air (e.g., [1,2,3,4,5,6,7,8,9,10,11,12]), and in fast longitudinal flows of air [13,14]. If the gas residence time in the discharge is small as compared with the vibrational-translational (V-T) relaxation time, the gas heating is almost suppressed and the gas is in a strongly non-equilibrium state (i.e., characterized by a level of vibrational energy which considerable exceeds its equilibrium value). These regimes, which correspond to relatively high electron number densities, 1018 –1019 m−3 , and relatively low gas temperatures, 2000–3000 K, are of interest for many practical applications, including plasma decontamination and sterilization, material processing, modification of electromagnetic waves propagation, and plasma aerodynamics The paper is organized as follows: Section 2 describes the numerical model, while the results and its discussion are presented in Section 3; Section 4 summarizes the conclusions
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