CFDWARP — 8-Species Air Plasma Finite Rate Chemical Solver  
The degree of ionization of the air plasma as well as its chemical composition is predicted within CFDWARP using a finite rate nonequilibrium 8-species 28-reactions model as outlined below in Table 1. The model [2] is especially suited to discharges in air at sea-level conditions. Additionally to chemical reactions related to ion-ion recombination, electron attachment, electron-ion recombination, and dissociation, the model also includes chemical reactions related to Townsend ionization (specifically reactions 1a and 1b in Table 1). Townsend ionization consists of an electron accelerated by an electric field impacting the nitrogen or oxygen molecules and releasing in the process a new electron and a positive ion. This chemical reaction is the physical phenomenon that is at the origin of sparks and lighting bolts and that occurs in a weakly-ionized plasma whenever the electric field reaches very high values. It needs to be included in the chemical model when solving plasma aerodynamics or plasma-assisted combustion in order to predict correctly the voltage drop within the cathode sheaths. Cathode sheaths are thin regions near the cathodes where the electric field is particularly high due to the current being mostly ionic.

Additionally to being capable to well predict low-temperature air plasmas ionized by electron beams, CFDWARP is also capable of solving finite rate hydrogen-air chemical reactions through the Jachimowsky model [53], kerosene-air chemical reactions through the Kundu model, and methane-air chemical reactions through the Yungster model [54].
[2]  B Parent, SO Macheret, MN Shneider, and N Harada, “Numerical Study of an Electron-Beam-Confined Faraday Accelerator,” Journal of Propulsion and Power, Vol. 23, No. 5, 2007, pp. 1023–1032.
[30]  B Parent, SO Macheret, and MN Shneider, “Electron and Ion Transport Equations in Computational Weakly-Ionized Plasmadynamics,” Journal of Computational Physics, Vol. 259, 2014, pp. 51–69.
[31]  NL Aleksandrov, EM Bazelyan, IV Kochetov, and NA Dyatko, “The Ionization Kinetics and Electric Field in the Leader Channel in Long Air Gaps,” Journal of Physics D Applied Physics, Vol. 30, 1997, pp. 1616–1624.
[32]  A Kossyi, AY Kostinsky, AA Matveyev, and VP Silakov, “Kinetic Scheme of the Non-Equilibrium Discharge in Nitrogen-Oxygen Mixtures,” Plasma Sources Science and Technology, Vol. 1, 1992, pp. 207–220.
[33]  EM Bazelyan and YP Raizer, Spark Discharge, CRC, Boca Raton, Florida, 1997.
[34]  YI Bychkov, YD Korolev, and GA Mesyats, Inzhektsionnaia Gazovaia Elektronika, Nauka, Novosibirsk, Russia, 1982, (Injection Gaseous Electronics, in Russian).
[35]  OE Krivonosova, SA Losev, VP Nalivayko, YK Mukoseev, and OP Shatalov, Khimiia Plazmy [Plasma Chemistry], edited by B. M. Smirnov, Vol. 14, Energoatomizdat, Moscow, Russia, 1987, p. 3.
[53]  CJ Jachimowsky, “An Analytical Study of the Hydrogen-Air Reaction Mechanism With Application To Scramjet Combustion,” TP 2791, NASA, 1988.
[54]  S Yungster, and M Rabinowitz, “Computation of Shock-Induced Combustion Using a Detailed Methane-Air Mechanism,” Journal of Propulsion and Power, Vol. 10, No. 5, 1994, pp. 609–617.
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