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

CEJAS, EZEQUIEL; MANCINELLI, BEATRIZ; PREVOSTO, LEANDRO

Plasma

mdpi

Año: 2020 vol. 3 p. 12 - 26

A model of a stationary glow‐type discharge in atmospheric‐pressure air operated in highgas‐temperature regimes (1000 K < Tg < 6000 K), with a focus on the role of associative ionizationreactions involving N(2D,2P)‐excited atoms, is developed. Thermal dissociation of vibrationallyexcited nitrogen molecules, as well as electronic excitation from all the vibrational levels of thenitrogen molecules, is also accounted for. The calculations show that the near‐threshold associativeionization reaction, N(2D) + O(3P)  NO+ + e, is the major ionization mechanism in air at 2500 K < Tg< 4500 K while the ionization of NO molecules by electron impact is the dominant mechanism atlower gas temperatures and the high‐threshold associative ionization reaction involving groundstateatoms dominates at higher temperatures. The exoergic associative ionization reaction, N(2P) +O(3P)  NO+ + e, also speeds up the ionization at the highest temperature values. The vibrationalexcitation of the gas significantly accelerates the production of N2(A3Σu+) molecules, which in turnincreases the densities of excited N(2D,2P) atoms. Because the electron energy required for theexcitation of the N2(A3Σu+) state from N2(X1Σg+, v) molecules (e.g., 6.2 eV for v = 0) is considerablylower than the ionization energy (9.27 eV) of the NO molecules, the reduced electric field begins tonoticeably fall at Tg > 2500 K. The calculated plasma parameters agree with the availableexperimental data.