Non-equilibrium Plasma Discharge Research Articles

Gliding Arc Plasma-Stimulated Conversion of Pyrogas into Synthesis Gas

This paper discusses plasma-assisted conversion of pyrolysis gas (pyrogas) fuel to synthesis gas (syngas, combination of hydrogen and carbon monoxide). Pyrogas is a product of biomass, municipal wastes, or coal-gasification process that usually contains hydrogen, carbon monoxide, carbon dioxide, water, unreacted light and heavy hydrocarbons, and tar. These hydrocarbons diminish the fuel value of pyrogas, thereby necessitating the need for the conversion of the hydrocarbons. Various conditions and reforming reactions were considered for the conversion of pyrogas into syngas. Nonequilibrium plasma reforming is an effective homogenous process which makes use of catalysts unnecessary for fuel reforming. The effectiveness of gliding arc plasma as a nonequilibrium plasma discharge is demonstrated in the fuel reforming reaction processes with the aid of a specially designed low current device also known as gliding arc plasma reformer. Experimental results obtained focus on yield, molar concentration, carbon balance, and enthalpy at different conditions.

Surface Streamer Discharge for Plasma Flow Control Using Nanosecond Pulsed Power

Nonequilibrium plasma discharges have been demonstrated to be effective in a variety of flow control applications. Traditionally, surface dielectric barrier discharge (sDBD) or spark gaps have been used due to the small size, weight, and cost of generating electronics. Nanosecond pulsed discharge in the form of streamers has similar physical properties to sDBD while alleviating its disadvantages, but it has remained relatively untested due to pulse generation requirements. New developments in compact pulsed power technology, however, have enabled the generation of surface streamer discharge using small and inexpensive pulse generators. Images of surface streamer discharge generated for plasma flow control are presented.

Genome shuffling of Trichoderma viride for enhanced cellulase production

Genome shuffling is an efficient approach for the rapid engineering of microbial strains with desirable industrial phenotypes. In this study, we used genome shuffling in an attempt to improve the cellulase production of the wild-type strain Trichoderma viride TL-124. The initial mutant populations were generated by ultraviolet (UV) irradiation, low-energy ion beam implantation and atmospheric pressure non-equilibrium discharge plasma (APNEDP). The mutants were subjected to recursive protoplast fusion. The cellulase activities of shuffled strains were assayed after solid-state fermentation using wheat straw, an economical raw material, as substrate. The shuffled strain T. viride F161, which was selected from among about 2,000 shuffled strains after two rounds of genome shuffling, exhibited a total cellulase activity of 4.17 U g-1 dry weight, which was 1.97-fold higher that of wild-type strain T. viride TL-124 (2.12 U g-1 dry weight). Analysis by random amplification of polymorphic DNA revealed genetic differences between the shuffled strains and the wild-type strain.

Strain improvement for enhanced production of cellulase in Trichoderma viride

The filamentous fungi Trichoderma species produce extracellular cellulase. The current study was carried out to obtain an industrial strain with hyperproduction of cellulase. The wild-type strain, Trichoderma viride TL-124, was subjected to successive mutagenic treatments with UV irradiation, low-energy ion beam implantation, atmospheric pressure non-equilibrium discharge plasma (APNEDP), and N-methyl-N'-nitro-N-nitrosoguanidine to generate about 3000 mutants. Among these mutants, T. viride N879 strain exhibited the greatest relevant activity: 2.38-fold filter paper activity and 2.61-fold carboxymethyl cellulase, 2.18-fold beta-glucosidase, and 2.27-fold cellobiohydrolase activities, compared with the respective wild-type activities, under solid-state fermentation using the inexpensive raw material wheat straw as a substrate. This work represents the first application of APNEDP in eukaryotic microorganisms.

UV and VUV Excilamps with High Peak Power

Design and output parameters of pulse sources of spontaneous UV and VUV radiation based on the non-equilibrium discharge plasma of high-pressures gases are presented in this paper. Emission characteristics of plasma of diffuse discharge preionized by runaway electrons and barrier discharge in rare gases and mixtures of rare gases with halogens have been investigated in gases at pressure up to 15 atm at excitation power up to 100 MW/cm3. The radiant power from 4π solid angle up to 1.2 MW with pulse duration of - 8 ns on Xe2* dimers were obtained at 12 atm pressure xenon. A high-voltage (up to 150 kV) short pulsed excitation mode was tested on dielectric barrier discharge KrCl- and XeBr-excilamps.

Effects of non-equilibrium plasma discharge on counterflow diffusion flame extinction

A non-equilibrium plasma assisted combustion system was developed by integrating a counterflow burner with a nano-second pulser to study the effects of atomic oxygen production on the extinction limits of methane diffusion flames at low pressure conditions. The production of atomic oxygen from the repetitive nano-second plasma discharge was measured by using two-photon absorption laser-induced fluorescence (TALIF). The results showed that both the atomic oxygen concentration production and the oxidizer stream temperature increased with the increase of the pulse repetition frequency for a constant plasma voltage. The experimental results revealed that the plasma activated oxidizer significantly magnified the reactivity of diffusion flames and resulted in an increase of extinction strain rates through the coupling between thermal and kinetic effects. Numerical computations showed that atomic oxygen quenching strongly depends on the oxidizer stream temperature. The kinetic effect of atomic oxygen production by a non-equilibrium plasma discharge on the enhancement of flame extinction limits was demonstrated, for the first time, at high repetition frequencies with elevated oxidizer temperatures. The reaction paths for radical production and consumption were analyzed. It was concluded that in order to achieve significant kinetic enhancement from atomic oxygen production on flame stabilization, the plasma discharge temperature needs to be above the critical crossover temperature which defines the transition point from radical termination to chain-branching.

Optical Emission Characteristics of Atmospheric-Pressure Nonequilibrium Microwave Discharge and High-Frequency DC Pulse Discharge Plasma Jets

With an aim to understand the mechanism of surface processing by atmospheric-pressure nonequilibrium discharge plasma jets, we measured the vibrational and rotational temperatures in the plasmas by means of optical emission spectroscopy (OES) measurement method. This paper focuses on the OES measurement method using a torch-shaped atmospheric-pressure nonequilibrium discharge plasma jet power supply consisting of a microwave (2.45-GHz) generator and a high-frequency (5.0-10-kHz) dc pulse power supply, using a gas mixture of Ar (8.0 L/min) and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (0.1-0.5 L/min) as the discharge plasma gas, and changing the flow rate of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas at the input power of 100-150 W. Upon comparing vibrational and rotational temperatures (0.18-0.27 eV) determined from the OES measurement method using two types of atmospheric-pressure nonequilibrium discharge plasma jets, results indicate that the microwave discharge plasma jet has considerably low vibrational and rotational temperatures.

Modeling of Mode Transition Behavior in Argon Microhollow Cathode Discharges

AbstractA self‐consistent, non‐equilibrium plasma discharge model is used to describe physical mechanisms and understand different operating regimes of a MHCD. The model includes a surface‐electric‐field dependent secondary electron coefficient description which is essential for the prediction of the different regimes of MHCD operation. At low current (&lt;0.1 mA), the plasma is confined within the cylindrical hollow region of the discharge. At currents above a certain threshold, the discharge expands over the outer flat surface of the cathode. Transient relaxation oscillations (self‐pulsing) of the discharge properties are predicted by the model for intermediate discharge currents ranging from about 0.1 to 0.3 mA.magnified image

Kinetic Ignition Enhancement of $\hbox{H}_{2}$ Versus Fuel-Blended Air Diffusion Flames Using Nonequilibrium Plasma

Kinetic ignition enhancement of H2 diffusion flames by a nonequilibrium plasma discharge of H2- and CH4-blended oxidizer was studied experimentally and numerically through the development of a well-defined counterflow system. Measurements of ignition temperatures and major species as well as computations of rates of production and sensitivity analyses were conducted to identify the important kinetic pathways. It was found that the competition between the catalytic effect of NOx and the inhibitive effects of H2O and CH4 governed the ignition processes in the system. With air as the oxidizer, ignition was enhanced from the plasma-produced NOx. With H2 addition to the oxidizer, H2O formation significantly increased the ignition temperature. However, with plasma activation, the inhibitive effect of H2O was significantly reduced because of the dominant role of NOx. With CH4 addition to the oxidizer, the ignition temperatures increased due to the radical quenching by H2O or CH4, depending upon the strain rate. The results showed that the inhibitive effects were significantly decreased with plasma activation. Unlike vitiated air ignition, plasma-enhanced ignition for fuel-air mixtures can suppress the inhibitive effects of H2O and CH4 because of the overwhelming catalytic NOx effect at low temperatures.

Kinetic Ignition Enhancement of Diffusion Flames by Nonequilibrium Magnetic Gliding Arc Plasma

Kinetic ignition enhancement of CH 4 -air and H 2 -air diffusion flames by a nonequilibrium plasma discharge of air was studied experimentally and numerically through the development of a well-defined counterflow system. Measurements of ignition temperatures and major species, as well as computations of rates of production and sensitivity analyses, were performed to understand the kinetic enhancement pathways for ignition by plasma discharge of air. It was found that plasma discharge of air led to significant kinetic ignition enhancement illustrated by large decreases in the ignition temperatures for a broad range of strain rates. Examination of the radical and NO x production in the plasma showed that the enhancement was caused primarily by the catalytic effect of NO x . The results of numerical simulations of the counterflow burner with preheated air and NO, addition showed the existence of different ignition regimes, which appeared due to the competition between radical production by NO x and other pathways, as well as heat release. There were two ignition regimes for small concentrations of NO, and three ignition regimes for large concentrations of NO,. Numerical simulations agreed well with the experimental measurements and suggested a new strategy for plasma-assisted ignition in supersonic flow, where a combination of thermal and nonthermal plasma would work more efficiently for ignition enhancement.

Removal of model proteins by means of low-pressure inductively coupled plasma discharge

Surgical instruments are intended to come into direct contact with the patients' tissues and thus interact with their first immune defence system. Therefore they have to be cleaned, sterilized and decontaminated, in order to prevent any kind of infections and inflammations or to exclude the possibility of transmission of diseases. From this perspective, the removal of protein residues from their surfaces constitutes new challenges, since certain proteins exhibit high resistance to commonly used sterilization and decontamination techniques and hence are difficult to remove without inducing major damages to the object treated. Therefore new approaches must be developed for that purpose and the application of non-equilibrium plasma discharges represents an interesting option. The possibility to effectively remove model proteins (bovine serum albumin, lysozyme and ubiquitin) from surfaces of different materials (Si wafer, glass, polystyrene and gold) by means of inductively coupled plasma discharges sustained in different argon containing mixtures is demonstrated and discussed in this paper.

Optimal discharge placement in plasma-assisted combustion of a methane jet in cross flow

Repetitively pulsed, nonequilibrium plasma discharges are studied for their ability to ignite and stabilize methane jet flames in cross flow air. The placement of the discharge is surveyed to optimize the flame duty cycle (stability). We find that flame ignition is not achieved when the discharge is located in the potential core region of the fuel jet or on the windward side of the most upstream part of the near field of the jet. A low (but nonzero) duty cycle is seen when the discharge is placed on the leeward side of the upstream near-field region. A high duty cycle (up to unity) is seen for discharge placement on both the leeward and windward sides of the downstream part of the near field. These results confirm that the effectiveness of the nonequilibrium discharge in stabilizing this flame depends on its placement in the complex scalar and velocity field. The mixture fraction at the discharge placement is characterized by plasma-induced breakdown spectroscopy (PIBS). The ratio of emission intensity of the CN band at 388 nm to the N 2 band at 337 nm is used to map the local equivalence ratio in the flow. We find that the methane mixture fraction at optimal discharge placements is lower than that where the flame resides in non-discharge-stabilized diffusion flames and is equal to that found in plasma-assisted methane jets in coflow air. Planar laser-induced fluorescence (PLIF) imaging of CH radicals is carried out to qualitatively understand the structure of the ignition flame kernel. The plasma discharge and flame base are spatially separated, suggesting that the discharge is a steady supplier of reactive species but not an instantaneous flame ignition source.

Protein film removal by means of low-pressure microwave plasma – an imaging ellipsometry study

Non-equilibrium plasma discharges have been recently proposed to be an effective tool for the removal of proteinaceous residuals from heat-degradable medical instruments. However, the knowledge regarding plasma-protein interactions is still relatively poor, which is a serious drawback for the validation of this technique as well as for its optimisation. This is, among other reasons, caused by the limitations of currently used techniques for monitoring of the rates of protein removal during plasma treatment. The objective of this article is to present an alternative method of evaluation of protein removal, based on imaging ellipsometry, which allows fast and semiquantitative analysis of the treatment efficiency.

Some Recent Topics of Non-equilibrium Discharge Plasma Technologies - Their Widespread Use from Low Pressure to Atmospheric Pressure

Non-equilibrium discharge plasmas have been utilized in a variety of fields and are indispensable to material processing, nanotechnologies and biotechnologies besides conventional applications such as light sources. In this review, neutral beam etching, advanced oxidation, protein removal, combustion control and volume, non-equilibrium discharge generation at atmospheric pressure are chosen and summarized as the recent, typical applications of the non-equilibrium discharge plasmas generated from low pressure to atmospheric pressure. A brief introduction of non-equilibrium discharge plasmas is also given, which serves comprehensive understanding of the physics and chemistry behind the technology.

Characterization of a Direct-Current Glow Discharge Plasma Actuator in Low-Pressure Supersonic Flow

DOI: 10.2514/1.27197 An experimental study of a direct-current, nonequilibrium glow plasma discharge in the presence of a Mach 2.85 supersonic flow is presented. The discharge is generated with pinlike electrodes flush-mounted on a plane surface with sustaining currents between 25 to 300 mA. In the presence of a supersonic flow, two distinct discharge modes (diffuse and constricted) are observed depending on the flow and discharge operating conditions. The effect of the dischargeonthe flow(“plasmaactuation”)ischaracterizedbytheappearanceofaweakshockwaveinthevicinityof the discharge. The shock is observed at low powers (10 W) for the diffuse discharge mode but is absent for the higher power (100 W) constricted mode. High-speed laser schlieren imaging suggests that plasma actuation is rapid as it occurs on a time scale that is less than 220 s. Rotational (gas) and vibrational temperature within the dischargeareestimatedbyemissionspectralline fitsofN2 andN 2 rovibronicbandsnear365–395nm.Theelectronic temperatures are estimated by using the Boltzmann plot method for Fe(I) atomic lines. Rotational temperatures are found to be high (1500 K) in the absence of a flow but drop sharply (500 K) in the presence of a supersonic flow for both the diffuse and constricted discharge modes. The vibrational and electronic temperatures are measured to be about 3000 K and 1.25 eV, respectively, and these temperatures are the same with and without flow. The gas temperature spatial profiles above the cathode surface are similar for the diffuse and constricted modes indicating that dilatational effects due to gas heating are similar. However, complete absence of flow actuation as indicated visually by the shock indicates that electrostatic forces may also play an important role in high-speed plasma-flow actuation phenomena. Analytical estimates using cathode sheath theory indicate thation pressure within sheath can besignificant,resulting ingascompressionwithin sheathandacorrespondingexpansionaboveit. Theexpansion,in turn, may fully negate the dilatational effect in the constricted case resulting in an apparent absence of forcing in the constricted case.

Modeling of Fluid Dynamics and Heat Transfer Induced by Dielectric Barrier Plasma Actuator

Glow discharge at atmospheric pressure using a dielectric barrier discharge can induce fluid flow, and can be used for active control of aerodynamics and heat transfer. In the present work, a modeling framework is presented to study the evolution and interaction of such athermal nonequilibrium plasma discharges in conjunction with low Mach number fluid dynamics and heat transfer. The model is self-consistent, coupling the first-principles-based discharge dynamics with the fluid dynamics and heat transfer equations. Under atmospheric pressure, the discharge can be simulated using a plasma–fluid instead of a kinetic model. The plasma and fluid species are treated as a two-fluid system coupled through force and pressure interactions, over decades of length and time scales. The multiple-scale processes such as convection, diffusion, and reaction/ionization mechanisms make the transport equations of the plasma dynamics stiff. To handle the stiffness, a finite-volume operator-split algorithm capable of conserving space charge is employed. A body force treatment is devised to link the plasma dynamics and thermo-fluid dynamics. The potential of the actuator for flow control and thermal management is illustrated using case studies.

Spectroscopic studies and rotational and vibrational temperature measurements of atmospheric pressure normal glow plasma discharges in air

DC normal glow (NG) discharges were created in atmospheric pressure air for a pin to plate type geometry. The rotational and vibrational temperatures of the discharge were measured by comparing modelled optical emission spectra with spectroscopic measurements from the discharge. The temperatures were measured as a function of discharge current, ranging from 50 µA to 30 mA, and discharge length, ranging from 50 µm to 1 mm. Rotational temperatures from 400 to 2000 K were measured over this range. Vibrational temperatures vary from 2000 K to as high as 5000 K indicating a non-equilibrium plasma discharge. Spectroscopic measurements were compared using several different vibrational bands of the 2nd positive system of N2, the 1st negative system of and the UV transitions of NO. NO and transitions were also used to determine the electronic temperature and density. The discharge temperature appears to be controlled by two cooling mechanisms: (1) radial conductive cooling which results in an increase in temperature with increasing discharge current and (2) axial cooling to the electrodes which results in a temperature saturation with increase in discharge current. The measured discharge temperature initially increases rapidly with discharge current then becomes nearly constant at a higher discharge current. Thus, radial cooling appears to dominate at lower discharge currents and the axial cooling at higher discharge currents. The vibrational temperature decreases with increasing rotational temperature due to increased vibrational to translation relaxation but the discharge remains non-thermal and stable over the range studied. The discharge appears to have a maximum vibrational temperature at the low current limit of the NG regime.

Experimental and numerical study of external plume Characteristics in microhollow cathode discharges

Microhollow cathode (MHC) discharges are a class of miniature nonequilibrium high-pressure plasma discharges characterized by intense radiation and high gas temperatures. A prominent plume-like structure envelopes the region immediately outside the hollow cathode and the plume optical characteristics provide a direct indication of discharge behavior. Optical emission imaging and self-consistent numerical simulation of the discharge and in particular the plume are compared. Experimental trends of the plume size and intensity with varying discharge parameters are similar to computational results.

A Universal Resonant Converter for Equilibrium and Nonequilibrium Plasma Discharges

This paper proposes a new system to ignite and to sustain a plasma discharge for different reactor configurations, using a single-series parallel high-frequency resonant converter. The different operation modes are analyzed, and their performance is verified in two applications: an equilibrium plasma discharge (electric arc) and a nonequilibrium plasma discharge (electric barrier at atmospheric pressure) with intensity current and voltage amplitude varying from 135 mA and 1050 V to 600 mA and 502 V, and operating the reactors at 60 Hz, 14 kHz, and 40 kHz. The principal features and results are remarked, such as its ease of adaptation to several regimes of discharge, by simply changing the operational frequency.

Plasma decomposition of carbon-bearing reactants

The decomposition of benzene and acetylene in electric carbon arc and non-equilibrium discharge plasmas was studied in order to produce carbon gas. The composition of various gaseous and condensed products (fullerenes, amorphous carbon and graphite, amino acids, aliphatic and aromatic hydrocarbons) were analysed and discussed in relation to the operating parameters.