Glow Discharge in a High-Velocity Air Flow: The Role of the Associative Ionization Reactions Involving Excited Atoms

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.

Modelling of an Atmospheric–Pressure Air Glow Discharge Operating in High–Gas Temperature Regimes: The Role of the Associative Ionization Reactions Involving Excited Atoms

“…The "fast" gas heating in chemical reactions [29] was also taken into account for reactions, where energy release was considered accompanied by the exothermic energy value on the right side of the reactions in Table A1 (Appendix A). More details in the equations of the model and the treatment of the source terms can be found in [17]. The radial heat loss by thermal conduction-the dominant discharge cooling mechanism under the present conditions [5]-was calculated, considering a parabolic radial profile for the gas temperature in a discharge column with a characteristic radius R of approximately 1 mm (e.g., [30]).…”

“…T e and T g are in Kelvin. Rate coefficients obtained with the help of the BOLSIG+ code were corrected in order to account for gains in electron energy in superelastic collisions [17]. Calculations were performed using rates for reactions (R22) and (R23) taken from [48].…”

“…Recently, a kinetic model [17] that considered associative ionization reactions involving N( 2 D, 2 P)-excited atoms was presented. The model was applied to the modelling of nonequilibrium air plasmas created by glow discharges in a fast longitudinal air flow.…”

“…On the other hand, for discharge conditions that the gas residence time in the discharge was larger than the V-T relaxation time (e.g., ambient air discharges), the molecular gas changed to a state close to the thermodynamically equilibrium one with a higher gas temperature, as in an arc discharge. In this work, a kinetic model [17] was used for simulation of stationary glow discharges operated in ambient air at high-gas-temperature regimes (1000 K < T g < 6000 K) over a wide current density range. The major difference between the kinetic schemes proposed in the literature for modelling atmospheric-pressure air glow discharges [3][4][5][6][7][8][9] and the one used in this work is that the present model takes into account ionization processes involving excited-state atomic collisions.…”

Atmospheric Pressure Plasmas in Material Science

“…This Special Issue consists of five research papers and one review paper in which fundamental properties of APP have been explored to advance our understanding of plasma complex interactions [ 2 , 3 , 4 ] in which APP was ignited using novel plasma source designs [ 2 , 5 ] and has been used in a wide range of applications, particularly in nanofabrication [ 2 , 3 , 6 ], biocatalysts immobilization [ 7 ], and energy-related processes [ 2 ].…”