Nonequilibrium Gas-discharge Plasma Research Articles

Simulation of filamentation dynamics of microwave discharge in nitrogen

The present study deals with numerical simulations of microwave (MW) discharges in nitrogen based on extended fluid-dynamic model. The set of governing equations for non-equilibrium gas-discharge plasma includes conservation equations for species number densities, electron energy density, Poisson equation for the electric field coupled to the multi-temperature Navier–Stokes fluid-dynamic equations taking into account thermal nonequilibrium; the power transmitted from MW radiation to electrons is determined from the Helmholtz equation. The kinetic scheme includes 61 reactions involving neutral molecules and atoms in the ground and electronically excited states, ions and electrons. The set of equations is solved for a two-dimensional problem under conditions of experiments at a pressure of 40 and 50 Torr and different electromagnetic wave frequencies and pulse duration. The dynamics of discharge formation and transition from the diffuse to the filament form is studied. The results are compared with experimental data, and a good agreement is shown for the time larger than 10 µs. The possible reasons for discrepancies at a shorter time are discussed and the effect of small oxygen impurities on the quantitative characteristics of the discharge are evaluated. The presence of a small oxygen impurity and seed electrons in the region of discharge formation yields a better agreement between numerical and experimental data.

Effect of water activated by non-equilibrium gas-discharge plasma on the germination and early growth of cucumbers

The article presents the results of plasma-chemical treatment of water and studies of its effect on the germination of cucumber seeds, as well as on the dynamics of the initial growth of 
 plants. Tap water was treated with a pulsed underwater discharge formed in vapor-gas bubbles near the surface of a graphite electrode immersed in water. The discharge burned at peak voltage values of 800 V and a discharge current of 200 mA. Oscillograms of the current and voltage on the electrodes were obtained, the values of the specific electrical conductivity of water, the pH value, the concentrations of nitrite and nitrate ions, and also hydrogen peroxide in the treated water were measured. It is shown that the application of the plasma treated water ncreases the seed germination, accelerates the development of the root system, the growth of stem and leaves at the early stages of plant development

Implicit and coupled fluid plasma solver with adaptive Cartesian mesh and its applications to non-equilibrium gas discharges

We present a new fluid plasma solver with adaptive Cartesian mesh (ACM) based on a full-Newton (nonlinear, implicit) scheme for non-equilibrium gas discharge plasma. The electrons and ions are described using drift–diffusion approximation coupled to Poisson equation for the electric field. The electron-energy transport equation is solved to account for electron thermal conductivity, Joule heating, and energy loss of electrons in collisions with neutral species. The rate of electron-induced ionization is a function of electron temperature and could also depend on electron density (important for plasma stratification). The ion and gas temperature are kept constant. The transport equations are discretized using a non-isothermal Scharfetter–Gummel scheme to resolve possible large temperature gradients in the sheaths. We demonstrate the new solver for simulations of direct current (DC) and radiofrequency (RF) discharges. The implicit treatment of the coupled equations allows using large time steps. The full-Newton method (FNM) enables fast nonlinear convergence at each time step, offering significantly improved simulation efficiency. We discuss the selection of time steps for solving different plasma problems. The new solver enables solving several problems we could not solve before with existing software: two- and three-dimensional structures of the entire DC discharges including cathode and anode regions, electric field reversals and double-layer formation, the normal cathode spot and an anode ring, moving striations in diffuse and constricted DC discharges, and standing striations in RF discharges. The developed FNM-ACM technique offers many benefits for tackling the disparity of gas discharge plasma systems' time scales and nonlinearity.

Plasma-Chemical Decomposition of Hydrocarbons on the Basis of the Micro-Arc Discharge with Disc Electrodes Rotating in the Bulk of Raw Materials

An innovative plasma-chemical hydrocarbon processing reactor has been developed. It is based on the interaction of nonequilibrium gas-discharge plasma with hydrocarbons in the bulk of a raw material. The results of experiments have shown that nonequilibrium gas-discharge plasma of micro-arc discharge, initiated in the bulk of hydrocarbon raw materials, is a unique tool for their processing. It is shown that this method allows not only decomposing hydrocarbons into light fractions, but also simultaneous obtaining fullerenes and nanotubes.

Characteristics of the effect of low-current gas discharge on a strong shock wave

The effect of nonequilibrium plasma medium created by low-current gas discharge on a shock wave (Mach number M = 6.8) has been investigated. The shock wave is generated in a shock tube with a circular cross section and then passes through the area of the effect in the working chamber having a square cross section. The gas discharge is ignited in the area of the effect before the arrival of the shock wave by applying voltage to special pin electrodes mounted in the upper and lower walls of the working chamber. In the experiment, the phenomenon of broadening of the shock wave and an increase of its propagation velocity when passing through the region of nonequilibrium gas-discharge plasma was discovered.

Influence of surface microwave discharge on ignition of high-speed propane-air flows

Ignition of supersonic propane-air flow under conditions of low-temperature plasma of surface microwave discharge is experimentally studied. We show that both rich and poor mixtures ignite, and the combustion intensity is maximal for the stoichiometric mixture. The dependence of the supersonic propaneair flow ignition time on the reduced electric field, E/n, under conditions of nonequilibrium gas-discharge plasma is experimentally obtained. The induction period is shown to decrease from 1 ms to 5 μs with the increase in E/n from 40 to 200 Td. The propagation velocity of the combustion front boundary (depending on the equivalent mixture ratio and the input microwave power) is maximal for the stoichiometric mixture and reaches 160 m/s at E/n = 150 Td. Under these conditions, the combustion temperature is about 3000 K.

Supersonic flow of a nonequilibrium gas-discharge plasma around a body

The flow of a nonequilibrium gas-discharge plasma around a semicylindrical body is studied. The aim of the study is to see how a change in the degree of nonequilibrium of the incoming plasma changes the separation distance between a shock wave and the body. Experiments are carried out with a supersonic nozzle into which a semicylindrical body is placed. The inlet of the nozzle is connected to a shock tube. In the course of the experiment, electrodes built into the wall of the nozzle initiate a gas discharge in front of the body to produce an additional nonequilibrium ionization in the stationary incoming supersonic flow. The discharge parameters are selected such that the discharge raises the electron temperature and still minimizes heating of the gas. The degree of nonequilibrium of the flow varies with gas-discharge current. Diagnostics of the flow is carried out with a schlieren system based on a semiconductor laser. The system can record flow patterns at definite time instants after discharge initiation.

Conversion of air mixture with ethanol and water vapors in nonequilibrium gas-discharge plasma

In search for an alternative fuel for internal combustion engines, we have studied the possibility of obtaining molecular hydrogen via the conversion of air mixture with ethanol and water vapors in a new plasma reactor. It is shown that, in agreement with experimental data, the H2 concentration is a linear function of the discharge current and decreases with increasing gas flow rate in the interelectrode gap. It is established that the proposed approach provides higher molecular hydrogen concentrations as compared to those achieved with other methods.

Effect of air on the concentration of molecular hydrogen in the conversion of ethanol by a nonequilibrium gas-discharge plasma

The effect of air on the concentration of molecular hydrogen in the conversion of ethanol by a nonequilibrium gas-discharge plasma is theoretically studied. Two models are developed to calculate plasma kinetics in two operation regimes of an experimental setup used for ethanol conversion into free hydrogen in order to increase the efficiency of the combustion of heavy hydrocarbon fuels. A comparison with the experimental results demonstrates that both of the models adequately describe the kinetics of the discharge reactions.

Plasma ignition of combustion in a supersonic flow of fuel-air mixtures: Simulation problems

Theoretical and experimental approaches to tackling the problems of plasma ignition of supersonic combustion in fuel-air mixtures of various compositions are discussed. Discharge types useful for this purpose are considered. The feasibility of reaching a substantial gain in energy in the initiation of combustion by non-equilibrium gas-discharge plasma is particularly interesting.

Effect of a Gas Discharge on the Ignition in the Hydrogen-Oxygen System

A kinetic model is constructed for ignition initiated by nonequilibrium gas-discharge plasma in the hydrogen-oxygen system. The model takes into account the effect of the electric field on the dissociation of molecules and on the buildup of active radicals, excited species, and charged species (electrons and positively and negatively charged ions). It is demonstrated by mathematical modeling that the induction period depends strongly on the reduced strength of the electric field (electron temperature). Four reduced kinetic networks are considered, and various components and reactions are shown to exert an effect on the nonthermal initiation of ignition in the H2-O2 system by low-temperature plasma.

Non-equilibrium properties of a flowing hydrogen cascaded arc plasma: kinetic modelling

A new kinetic scheme of the non-equilibrium gas discharge plasma is employed to describe the characteristics of a low-pressure cascaded arc plasma in pure hydrogen. The presented kinetic model includes the dynamics of the following plasma components: vibrationally excited hydrogen molecules in the ground electronic state , hydrogen atoms in the ground and electronically excited states (H(n), n=1,2,...) and electrons, positive and negative hydrogen ions . It has been shown that the low-pressure hydrogen cascaded arc plasma is characterized by high degrees of ionization and dissociation, and can generate high-density fluxes of vibrationally excited hydrogen molecules and negative ions.

Drift oscillations of the gas-discharge plasma in magnetic field at low electron densities

An experimental and theoretical study of the drift oscillations in a non-equilibrium gas-discharge plasma with a density gradient across a magnetic field at low electron densities was carried out. The solution of the set of differential equations for the bounded cylindrical plasma is used to describe unstable oscillations in the plasma de-stabilized by the action of non-quasi-neutrality in perturbations and ion inertia simultaneously.

Generators of nonequilibrium low-temperature plasma

Results are described of a study and of the characteristics of sources of a non-equilibrium gas-discharge plasma.