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The gliding arc cold plasma treatment of wheat seeds is an alternative to chemical seed dressing, but this treatment is not very effective. This study was focused on testing the addition of salt, water and nitrogenous compounds during plasma treatment to increase the efficiency of the plasma seed treatment. The additives were not supplied in the gaseous state, as usual, but in an aqueous solution by spraying under a plasma nozzle during the treatment. The phytosanitary effect of the plasma treatment was evaluated based on the germination of Tilletia caries spores from artificially infected seeds on water agar. The viability of the seeds, growth and yield characteristics of the plasma-treated seeds were evaluated in the laboratory, greenhouse and even in field experiments with the primary goal of reducing spore vitality. The germination of T. caries spores was mostly limited to the variant with the addition of water during plasma treatment, where spore germination reached only 32.7% of the control variant while maintaining sufficient growth properties. The experiment demonstrated the suitability of using the addition of various substances during plasma treatment in the form of aqueous solutions and increasing the effectiveness of this treatment.

The formation of a plasma jet by a glow discharge in an air flow in the electrode system of a so-called gliding arc is considered at an average discharge current of 100 mA and an air flow rate of 0.1 g/s. The displacement of a negative glow region over the cathode surface is analyzed using a sectioned plane cathode. A method for the plasma jet diagnostics by measuring the charged particle current on a special diagnostic electrode placed inside the jet is proposed. Based on the data obtained, the characteristic features of the current transfer inside the jet are obtained. The charged particle concentration inside the jet is estimated for the proposed current transfer model. [ABSTRACT FROM AUTHOR]

The gliding arc cold plasma treatment of wheat seeds is an alternative to chemical seed dressing, but this treatment is not very effective. This study was focused on testing the addition of salt, water and nitrogenous compounds during plasma treatment to increase the efficiency of the plasma seed treatment. The additives were not supplied in the gaseous state, as usual, but in an aqueous solution by spraying under a plasma nozzle during the treatment. The phytosanitary effect of the plasma treatment was evaluated based on the germination of Tilletia caries spores from artificially infected seeds on water agar. The viability of the seeds, growth and yield characteristics of the plasma-treated seeds were evaluated in the laboratory, greenhouse and even in field experiments with the primary goal of reducing spore vitality. The germination of T. caries spores was mostly limited to the variant with the addition of water during plasma treatment, where spore germination reached only 32.7% of the control variant while maintaining sufficient growth properties. The experiment demonstrated the suitability of using the addition of various substances during plasma treatment in the form of aqueous solutions and increasing the effectiveness of this treatment. [ABSTRACT FROM AUTHOR]

Hybrid plasmas have been reported in various areas of research over the last 40 years. However, a general overview of hybrid plasmas has never been presented or reported. In the present work, a survey of the literature and patents is carried out to provide the reader with a broad view of hybrid plasmas. The term refers to several different configurations of plasmas, including but not limited to: plasmas driven by several power sources simultaneously or sequentially, plasmas that have the properties of both thermal and nonthermal plasmas, plasmas that are enhanced by additional energy, and plasmas that are operated in a unique medium. In addition, a way of evaluating hybrid plasmas in terms of the improvement of processes is discussed, as well as the negative impacts that follow the employment of hybrid plasmas. Regardless of what the hybrid plasma in question is composed of, it often poses a unique advantage to its nonhybrid counterpart, whether it be used for welding, surface treatment, materials synthesis, coating deposition, gas phase reactions, or medicine. [ABSTRACT FROM AUTHOR]

A reverse vortex flow gliding arc discharge in a fuel-rich premixed mixture was applied to a high swirl fuel-lean global combustion to accelerate fuel oxidation. Both the discharge and flame were generated in natural gas and air. To evaluate the role of the gliding arc in the process, a gas analysis of the exhaust gas was performed in the same operational conditions with and without plasma. The chemical measurements show that the plasma reduces carbon monoxide and unburned hydrocarbons contents with a low impact on the NOx level. Furthermore, the comparison of the relative decrease of the hydrocarbon emissions shows that the hydrocarbons have different sensitivities to the plasma application. [ABSTRACT FROM AUTHOR]

Aiming at understanding the role of CH4/CO2 ratio on gliding arc (GA)‐based dry reforming of methane (GA‐DRM), the GA‐DRM at CH4/CO2 ratio range of 0.11 to 1 was studied with kinetics simulation. The radicals of H, OH, and CH3 are identified as the main reactive species to induce the reactant conversion and product formation in GA‐DRM. The increase of CH4/CO2 raises the concentrations of H and CH3 and reduces the OH concentration. Subsequently, the CH4/CO2 ratio regulates the main reaction routes of GA‐DRM. The dehydrogenation coupling reaction enhances with CH4/CO2 and thus raises the selectivities of C2 hydrocarbons. The OH‐induced reactions for OH to H2O weaken with CH4/CO2, thereby increasing the H2 selectivity. [ABSTRACT FROM AUTHOR]

In this paper, the collaboration of a GlidArc-type plasma reactor with four dedicated power supplies was analysed. Each power supply is characterised by a different design solution. Plasma generation by electrical discharge requires a careful analysis of the power supply design, its operating characteristics, currents, voltages and frequencies. Although the power supplies tested have similar abilities and provide similar power supply parameters, different plasma reactor performance characteristics are obtained for each of them. The results indicate that some power supply parameters were overestimated or underestimated at the design stage. Some of the power supplies tested under plasma reactor load also show poor interaction with the mains. The interaction of the power supplies with the plasma reactor and the mains supply is strongly influenced by the type of plasma gas. Analyses indicate that an optimally designed power supply should combine the solutions contained in each of the power supplies tested. [ABSTRACT FROM AUTHOR]

The three‐dimensional (3D) vortex gliding arc plasmatron (GAP) is a promising gliding arc source due to its high reactant conversion rate and high energy efficiency, but there are few studies of its discharge characteristics. In this work, a 3D GAP device with a quartz window on the inner electrode is designed and studied. By means of high‐speed photography, high‐resolution current/voltage signal acquisition, and emission spectra, the effects of arc current, gas flow rate, electrode diameter, and electrode polarity on the discharge characteristics of this GAP are investigated. Results show that the volt‐ampere characteristic of GAP can be accurately predicted by similarity theory, and that the voltage for reverse‐polarity is significantly greater than that for normal‐polarity. Arc dynamics show that the arc at the inner electrode has the feature of high‐speed rotation, while the arc at the outer electrode has an extended current channel along with a large‐scale re‐strike process. The rotation speed and current channel length are closely related to electrode polarity, which can be ascribed to the movability of the cathode arc root. Emission spectra confirm that the plasma produced by GAP has typical non‐equilibrium properties, in which the rotational temperature ranges from 2,400 to 3,000 K and the vibrational temperature from 4,700 to 6,000 K. Moreover, abundant active free radicals, including NO, N2+$$ {\mathrm{N}}_2^{+} $$, O, and N, are detected in the plasma region. This investigation provides a better understanding of the discharge characteristics of 3D GAP, and will help to guide its further design and application. [ABSTRACT FROM AUTHOR]

A new atmospheric pressure non-equilibrium plasma source named the 'Propeller Arc' (PA) is developed using the concept of rotating electrodes. The PA device consists of a rotating cathode, driven by a motor, with one or more fixed anodes. Plasma is ignited at or near the narrowest gap as the rotating cathode passes by the anode and then it is extended up to a length of ∼66 mm or longer depending on the supplied power. This allows for efficient ignition, followed by a quick increase in plasma volume. The PA is similar to the widely used gliding arc (GA); however, unlike the GA, PA does not require imposed gas flow, and the PA discharge frequency can be easily controlled by the motor angular velocity. In this paper, the basic characteristics of PA are investigated using two different operation modes: pulse modulation and DC power. Discharge properties including electrical characteristics, time-resolved optical emission images, plasma electrical properties such as resistance and average electric field (discharge voltage divided by gap distance) and plasma power consumption are reported. Use of multiple anodes to increase the plasma volume is also demonstrated. As the PA has a compact design and is relatively easy to stabilize and control without the need for applied gas flow, it has potential to be adapted for many different applications such as nitrogen fixation, fuel and carbon dioxide conversion, waste, odor and hydrogen sulfide treatment, etc.

The plasma pyrolysis and plasma catalysis of methane coupling were performed under room temperature and atmosphere. The coupling of methane through gliding arc plasma with different H 2 /CH 4 ratios and N 2 flow rates exhibited conversion from 25% to 40% and high selectivity of acetylene above 90%. Plasma emission spectra displayed lowest I Hβ /I Hα ratio at H 2 /CH 4 ratio of 3, while I Hβ /I Hα ratio decreased with increasing N 2 feed rate from 0 to 2 L/min, which had similar variation with selectivity of acetylene. X-ray photoelectron spectra for reduced catalysts demonstrated that metallic Pd species (335.4 eV) were transferred to electron-rich Pd species (334.8eV and 334.1 eV) with increasing Pd loading and Ag/Pd ratio, corresponding to red shift of linear adsorbed CO stretching frequency from 2060 to 2068 cm−1 to 2055-2015 cm−1. Superior plasma catalytic behavior over 0.1Pd0.5Ag/Al 2 O 3 catalyst has been reached with 86.5% selectivity of ethene and 36.2% conversion of methane. • Methane coupling to ethene can achieve high yield of 30.2% through plasma catalysis. • Gliding arc plasma made high gas temperature leading to more acetylene production. • Proper AgPd catalyst exhibited great suitability for plasma catalysis process. [ABSTRACT FROM AUTHOR]

The need for energy resources that do not belong to the group of fossil fuels and a wide availability of various low-calorific gases leads humanity to search for solutions to adapt external sources of force that would allow for the use of these resources. One of such solutions is the usage of non-thermal plasma applications for pre-ignition stage, ignition, and, finally, combustion. Plasma assistance is a promising technology for improving processes of ignition and flame stabilization, as well as propagating flame speed. This study focuses on influence of the non-thermal plasma on both for CH4, CO2 gases, and their mixture in pre-ignition stage by performing emission spectroscopy, and determining tendency of excited species at different frequency rates for optimal plasma parameters to reduce NO formation and increase efficiency during combustion. The results obtained exhibit a non-linear dependence of radical's emission from the frequency of plasma. As an example of possible profits from correctly choosing plasma parameters, the calorific value of gases increased from 2.86 times for BG25/75 to 4.78 times for BG30/70. However, the decomposition on higher frequencies causes higher rates of nitrogen-bands emissions, which would increase NOx emissions in the combustion process. [ABSTRACT FROM AUTHOR]

Aiming at a deep understanding of the reaction kinetics of gliding arc (GA) plasma reforming, a new approach to combining simulation and experiment is reported. By adding thermodynamic module and conservation equations of mass and energy into the conventional 0D plasma kinetics model, an effective link between experimental diagnostics and reaction kinetics simulation is established for dry reforming of CH4 in GA plasma. The GA plasma parameters are diagnosed experimentally as electron density of 1.4 × 1014 cm−3, electron temperature of 1.5 eV, and arc gas temperature of 2500 K. The kinetics simulation is implemented based on the obtained plasma parameters and verified by the online analysis of gaseous products. Consequently, the reaction mechanism is revealed by the reliable model. [ABSTRACT FROM AUTHOR]

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Ammonia as a non-carbon fuel is expected to play an important role in the future, but it is difficult to be effectively utilized at this stage due to its flame retardancy and other characteristics. Therefore, we propose to use gliding arc plasma combined with a swirl burner to enhance the combustion performance of ammonia. The electrical characteristics, electron density, gas rotational temperature and the distribution of key active species in the burner were studied via optical emission spectroscopy (OES). With the increase of equivalence ratio (EQR), the width of the Hα line decreases significantly, indicating that the electron density shows a downward trend, even as the gas rotational temperature shows an upward trend. When the equivalence ratio was 0.5, the gas rotational temperature increases by about 320 K compared with the pure air condition. During pure air discharge, there will still be obvious NO emission due to the plasma reaction, but with the addition of NH3, the NO content in the emission is significantly reduced. The light intensity of O atoms in the burner gradually decreases with the increase of the equivalence ratio, the light intensity of H atoms increases first and then decreases, and the light intensity of NH shows an upward trend. The reason may be that the plasma discharge effectively strengthens NH3(E)->NH2+H, NH2+H->NH+H2 and other reactions promote the initial reaction step of NH3 which thus effectively strengthens the NH3 combustion. [ABSTRACT FROM AUTHOR]

This paper deals with the investigations of a low-current glow-type discharge in air flow as applied to the problem of nitrogen oxide production. The electrode configurations correspond to the classical coaxial plasmatron and to the so-called gliding arc. The discharge burns in a regime of constricted positive column with a typical current density from 47 to 120 A/cm2 and with the related electron density from 0.53⋅1014 to 2.3⋅1014 1/cm3. The gas temperature changes from 3000 to 3610 K. The described conditions provide a flow of NO molecules from the plasma column with the energetic cost for production of one molecule of (30–50) eV. Maximum content of NO molecules [NO] = 4 g/m3 (3500 ppm) was obtained. In spite of a rather high gas temperature, the plasma is still nonequilibrium. The high vibrational levels of the nitrogen molecules are populated, and the main channel of the nitric oxide production is associated with the reaction in which the vibrationally excited nitrogen interacts with atomic oxygen. [ABSTRACT FROM AUTHOR]

Nonthermal plasma (NTP) is a promising technology for the removal of persistent organic contaminants in wastewater thanks to its ability to generate powerful oxidizing species. In this work, a gliding arc discharge NTP was used for an experimental study to investigate the influence of relative humidity (RH) on reactive species generation depending on a plasma atmosphere (air and oxygen). In addition, an organic dye, Eriochrome Black T (EBT), was treated to investigate the removal potential of this plasma. Dimethyl sulfoxide was used as chemical probe for the detection of OH• and as a radical scavenger to explore the role of OH• in EBT removal. Hydrogen peroxide, nitrite, and nitrate quantification was also assessed. Results indicated that for air plasma, a RH of 30% contributed to the highest oxygen species generation, while dry conditions gave the best results under O2 plasma. The treatment of EBT revealed that humid air plasma (RH=30%) is more effective regarding decolorization. However, mineralization experiments showed that O2 plasma is more capable of mineralizing an EBT solution. The use of a radical scavenger showcased the potential of plasma gliding arc in humid air for the removal of organic contaminants when radicals' reactivity is inhibited. Therefore, this study may provide an effective and feasible method of applying NTP in wastewater treatment. [ABSTRACT FROM AUTHOR]

The treatment of produced water, associated with oil & gas production, is envisioned to gain more significant attention in the coming years due to increasing energy demand and growing interests to promote sustainable developments. This review presents innovative practical solutions for oil/water separation, desalination, and purification of polluted water sources using a combination of porous membranes and plasma treatment technologies. Both these technologies can be used to treat produced water separately, but their combination results in a significant synergistic impact. The membranes functionalized by plasma show a remarkable increase in their efficiency characterized by enhanced oil rejection capability and reusability, while plasma treatment of water combined with membranes and/or adsorbents could be used to soften water and achieve high purity. [ABSTRACT FROM AUTHOR]

In this paper, the collaboration of a GlidArc-type plasma reactor with four dedicated power supplies was analysed. Each power supply is characterised by a different design solution. Plasma generation by electrical discharge requires a careful analysis of the power supply design, its operating characteristics, currents, voltages and frequencies. Although the power supplies tested have similar abilities and provide similar power supply parameters, different plasma reactor performance characteristics are obtained for each of them. The results indicate that some power supply parameters were overestimated or underestimated at the design stage. Some of the power supplies tested under plasma reactor load also show poor interaction with the mains. The interaction of the power supplies with the plasma reactor and the mains supply is strongly influenced by the type of plasma gas. Analyses indicate that an optimally designed power supply should combine the solutions contained in each of the power supplies tested.

This study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma‐activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans. [ABSTRACT FROM AUTHOR]

In this article, a nonthermal gliding arc discharge (GAD) was generated in an air flow driven by a 40-kHz alternating current (ac) constant-current electric power supply. The influence of gas flow rate on the discharge characteristics of gliding arc was investigated using electrical diagnostics and fast Fourier transform (FFT) analysis method. The average discharge power, total harmonic distortion rate of arc voltage (THD ${_{u}}$), total harmonic distortion rate of arc current (THD ${_{i}}$), and the resistance of arc were experimentally studied. As the air flow rate increased from 4 to 12 L/min, it was found that the average discharge power of the gliding arc gradually decreased from 407.9 to 187.8 W. However, because of the nonlinear characteristics of the GAD circuit, with air flow rate increasing, both THDu and THDi linearly increased, while the resistance of arc gradually decreased from 26.3 to 14.1 $\text{k}\Omega $. Totally, the air flow rate influenced the discharge characteristics of the gliding arc mainly by ruling the average discharge power. Finally, for a better understanding of the discharge characteristics of the gliding arc, a discharge circuit model was further analyzed based on the average discharge power and reactive power. [ABSTRACT FROM AUTHOR]

Re-pulsing glow discharges in gaps up to 2 cm were experimentally investigated in atmospheric pressure air. Discharge was ignited as a sequence of spark and glow discharge and sustained in a glow regime after ignition. It was confirmed that the discharge with defined parameters could be ignited without any adjustments after initiation of the discharge. The discharges were characterized by a high-speed camera, current and voltage measurements, and optical emission spectrometry (OES). Typical structure of the glow discharge consisting of cathode glow, dark faraday space, positive column, and anode glow was observed. Transition from subnormal to normal glow mode was confirmed by analysis of current and voltage waveforms. It was found by OES that the type of discharge strongly affects the ratio of produced reactive species. It was confirmed that with change of discharge from subnormal to normal glow regime, rotational temperature could vary across a wide range (from 1650 to 3500 K). The developed device allows glow discharge to be ignited with defined parameters, which makes the control of the gas temperature and ratio of reactive species possible by presetting the discharge parameters. Additionally, it was demonstrated that corona discharge or repeating spark discharges could also be generated using the developed device without additional manipulations of the experimental setup by adjusting the discharge parameters.

Re-pulsing glow discharges in atmospheric-pressure air were experimentally investigated using a push-pull generator with pulse-width modulation. Discharges were ignited as a spark-glow discharge sequence and sustained in a glow regime after ignition in a gap of 2 cm and characterized by current and voltage measurements, as well as by optical emission spectroscopy. It was found that at a certain range of parameters, the discharge could be stabilized even in the presence of external airflow. It was demonstrated that the type of discharge and total power dissipated in the plasma volume could be precisely controlled by pulse-width modulation. Additionally, it was confirmed that the rotational temperature varied across a wide range (1640-2440 K) by using pulse-width modulation with gas-flow control, when vibrational temperature was around 4610 ± 770 K. The generation of stable glow discharge in the presence of gas flow with a wide range of parameters that could be precisely controlled by pulse-width modulation looks promising for use in energy-efficient gas conversion.

Non-thermal plasma technology is an interesting method for removalof tar from gasified biomass. In this study, AC gliding-arc reactors with a reverse vortex flow configuration were developedfor biomass tar treatment. Successful generation of plasma discharge was obtained at high volume flowsof treated gas. Preliminary experimental results showed that the onset of electric discharge occurred at about 10 kV. A large numberof plasma discharges was evident. For our developed prototype, electric power input, total gas feed rate, and variouscarrier gases(Air, N2, N2+C10H8) were adjusted to investigate their effects on the dischargephenomena.The reverse vortex flow gliding arc discharges showed high residence timesfor potential chemical reactions inside the reactor. From preliminary tests, maximum removal efficiency of a representative tar compoundof more than 93%was found, atanenergy utilization efficiencyof about 30 g/kWh.

The design of efficient plasma reformers requires both efficient fuel conversion of fuel and chemical energy extraction. In this regard, liquid fuels provide the advantages of high gravimetric and volumetric energy densities, therefore yielding high energy; in particular, diesel is promising for use in plasma reformers. In this study, we investigated the ignition process in a diesel reformer driven by a rotating gliding arc using a high-speed camera. The locations of the flame kernel generated by the arc were clearly identified under different power conditions. At high power, the flame kernel was generated at the nozzle tip, which grew into a fully developed flame. This indicates that the period for fuel vaporization and mixing with air (which is a necessary step prior to chemical reactions and is typically longer than the characteristic chemical reaction time) is extremely short. Moreover, with low oxygen concentrations, we observed a rotating flame kernel. At low power, the flame kernel was generated at a distance from the nozzle tip and the arc. This result indicates that the generation mechanism of the flame kernel in the plasma reformer is not straightforward; flow and arc dynamics also influence the interactions between the arc and fuel droplets. [ABSTRACT FROM AUTHOR]

In this research, the polypropylene (PP) sheets used for automotive bumper surface were treated using two methods: air atmospheric gliding arc plasma and flame modifications. Atomic force microscopy was applied to study the morphology of surfaces before and after treatment processes. While calculating the surface free energy (SFE), contact angle of the surfaces was measured, and the chemical composition of the PP surface was analyzed using X‐ray photoelectron spectroscopy. Surface modifications by gliding arc plasma increased the ratio of the oxygen and nitrogen atoms on the surface by 100%, indicating that polar chemical functionalities form on the surface. The surface morphology was highly affected by gliding arc plasma treatments, which triggered an impact on roughness and etching. It was also found that the SFE was drastically increased by certain modifications. Noticeable improvement was also observed in wettability by the gliding arc plasma technique. In the next stage, polyurethane paints were coated on the treated and untreated PP surfaces. Then, we examined the flame and gliding arc plasma treatments' effect on coating properties of PP bumper, adhesion analysis, water immersion resistance, and sulfuric acid resistance. Finally, high‐pressure carwash test and gloss analysis were conducted on the treated and untreated coated sheets, respectively. [ABSTRACT FROM AUTHOR]

The mass transfer and energy efficiency in the "batch" and "Circulating" gliding arc configuration reactors for the direct discharges and degradation of pollutants in the aqueous solution have been investigated. The mass transfer characterization and energy efficiency in this study showed that the "Batch" configuration would be more efficient than the "Circulating" reactor. The difference between these reactors is due to the plasma (gas)–solution (liquid) contact time, therefore the gas–liquid transfer phenomenon. The lowest value of pH (2.5) and high temperature obtained in the "Batch" reactor contributes to better nitrogen oxides (NOx) transfer and solubility consequently the high conversion of the phenol in this reactor configuration (100% after 10 min of treatment) relative to that obtained in the circulating reactor (≈ 50% after 30 min) with pH 4.7. [ABSTRACT FROM AUTHOR]

Activated carbon has been extensively utilized to adsorb pollutants generated by industrial activities. There have been many attempts to efficiently produce activated carbon from spent coffee grounds in the field of environmental technology. In this study, the feasibility of the novel production of activated carbon from coffee ground waste using a plasma jet was evaluated. A rotating gliding arc generator was designed that used an N2 plasma jet for the carbonization process and a CO2 plasma jet for the activation process. It was confirmed that the coffee ground waste could be carbonized and activated by the two plasma jets in the same reactor. The characteristics of the surface morphologies of the activated carbon samples varied depending on the plasma treatment conditions, such as the electric power of the plasma jet and the treatment time. The results implied that the adsorption capacity of the activated carbon could be optimized by regulating the pore size and distribution based on the plasma treatment conditions with regard to the molecular size of the target adsorbate.

There is increasing interest in plasma technology for CO2 conversion because it can operate at mild conditions and it can store fluctuating renewable electricity into value-added compounds and renewable fuels. This perspective paper aims to provide a view on the future for non-specialists who want to understand the role of plasma technology in the new scenario for sustainable and low-carbon energy and chemistry. Thus, it is prepared to give a personal view on future opportunities and challenges. First, we introduce the current state-of-the-art and the potential of plasma-based CO2 conversion. Subsequently, we discuss the challenges to overcome the current limitations and to apply plasma technology on a large scale. The final section discusses the general context and the potential benefits of plasma-based CO2 conversion for our life and the impact on climate change. It also includes a brief analysis on the future scenario for energy and chemical production, and how plasma technology may realize new paths for CO2 utilization.

In order to solve the problem of small and asymmetrical plasma area of the gliding arc (GA) in the chemical treatment process, a plasma actuator driven by alternating current (AC) with a frequency of 23.2kHz was designed to multichannel gliding arcs (MGAs) in a rotational air flow at atmospheric pressure. The spatiotemporally resolved discharge characteristics of the MGA, including long-length breakdown, long-term extinction and typical breakdown features, were investigated combining optical and electrical diagnostic methods simultaneously at a flow rate of 250 SLM (standard liter per minute). The response characteristics of MGA under different flow rates were analyzed. On average, the MGA exhibit 48.8% more discharge power compared to traditional single-channel GA under flow rates of 50–250 SLM, which is due to the GAs continual existence at long-length state, representing better stability of the MGA plasma actuators. It was observed that the frequency of typical breakdown and long-term extinction increased as the flow rate accelerated, and the maximum height the GA could reach decreased with the number of channels increasing from 1 to 5, which can be attributed to the power decline of separate channels of GAs at 50 SLM. It was also found that MGA showed a broader plasma distribution of low electron temperature than traditional single-channel GA. [ABSTRACT FROM AUTHOR]

Controllability of the kinetic path of methane conversion in plasma driven oxidation reaction is investigated. Different geometries in a rotating gliding arc reactor are adopted to control reaction paths in methane oxidation reaction. Diverging and converging type reactor product different reaction environments in view point of both the reaction time and the degree of thermal activation. In the diverging reactor, the partial oxidation process is dominant with high methane conversion because the diverging section facilitates to elongate the arc length and decrease the flow velocity. Thus, the convective and radiative heat transfer from the arc column to the reactants could be enhanced. The role of plasma in the diverging reactor is mainly igniting and sustaining the partial oxidation, which is rather different from that in the converging reactor where the plasma plays as a heat source for thermal pyrolysis of methane with the help of focusing thermal energy of the arc. • Geometry of rotating gliding arc reactor affects methane oxidation processes. • Diverging type reactor head is beneficial for the partial oxidation process. • Converging type reactor head is advantageous for the pyrolysis process. [ABSTRACT FROM AUTHOR]

To disclose water roles in plasma reforming of methanol for hydrogen production, gliding arc discharge characteristics, optical emission spectra, and reaction behavior are investigated over a water concentration range of 0–95 mol%. It can be concluded that the varied reaction behavior with water concentration derives from three water roles as a homogeneous catalyst, CO oxidant, and side‐product. The former two roles of water are beneficial for hydrogen production. The side‐product role of water, accompanied by hydrocarbons formation, which is disadvantageous to hydrogen production and can be almost fully inhibited by the homogeneous catalysis of water at above 33 mol% H2O. As an oxidant, water conversion is controlled by the thermodynamic equilibrium at the gas temperature of arc. [ABSTRACT FROM AUTHOR]

We studied hydrogen sulfide (H2S) decomposition into hydrogen (H2) and sulfur (S2) in a gliding arc plasmatron (GAP) and microwave (MW) plasma by a combination of 0D and 2D models. The conversion, energy efficiency, and plasma distribution are examined for different discharge conditions, and validated with available experiments from literature. Furthermore, a comparison is made between GAP and MW plasma. The GAP operates at atmospheric pressure, while the MW plasma experiments to which comparison is made were performed at reduced pressure. Indeed, the MW discharge region becomes very much contracted near atmospheric pressure, at the conditions under study, as revealed by our 2D model. The models predict that thermal reactions play the most important role in H2S decomposition in both plasma types. The GAP has a higher energy efficiency but lower conversion than the MW plasma at their typical conditions. When compared at the same conversion, the GAP exhibits a higher energy efficiency and lower energy cost than the MW plasma. [ABSTRACT FROM AUTHOR]

In this work, we developed a portable device with low production and operation costs for generating ambient-air glow discharge (AAGD) that is transferred to the surface of flowing liquid and demonstrated its applicability to practical use in agriculture. An experiment procedure that ensured the stable treatment of various liquids was established. Additionally, it was found that humidity did not have a significant effect on the treatment process, which makes the use of the developed device possible in various locations. It was found that an L-phenylalanine solution treated with AAGD allows simultaneous 40% hydroponic radish-sprout growth promotion with a bactericidal effect. Further, scalability and practical-application possibilities in hydroponic plant growth were discussed. [ABSTRACT FROM AUTHOR]

Gliding arc is a mostly used non-equilibrium plasma generation method whose characteristic is affected by the back-breakdown phenomenon. Mode transition induced by back-breakdown of the gliding arc is studied in this work and effects of gas flow rate, applied voltage, electrode parameters on mode transition were studied. Experimental results show that there are two typical modes during the development of the gliding arc. Mode A comprises periodicitical development of the arc from the minimum gap breakdown to the longest extinguishment, while the arc in mode B continues to produce a back-breakdown at the ends of the electrodes. As the flow rate descends, the gliding arc gradually changes from mode A to B. It is the decrease of the arc velocity caused by lower flow rate leads to the occurrence of back-breakdown, which generates mode B. Smaller electrode opening angle, shorter length and wider minimum gap reduce the gliding speed, so that arc is more likely to enter mode B. As the applied voltage is increased, enhancing of the electric field strength on the breakdown path of the back-breakdown and thickening of the arc's diameter allow the gliding arc to enter mode B at a higher arc speed.

Hydrogen produced from CH 4 –CO 2 reforming by an optimized rotating gliding arc discharge plasma reactor is investigated in this study. The effect of CH 4 /CO 2 ratio (mole ratio), total input flow rate, discharge gap, voltage, and discharge frequency are analyzed. The results show that H 2 yield increases with the increase of CH 4 /CO 2 ratio. Arc can be stretched effectively by increasing total input flow rate, then the discharge region is enlarged. Increasing discharge gap can enlarge the discharge region, but the reaction of the gas mixture would be suppressed if the discharge region was excessively large. The discharge region decreases with the increased discharge frequency to a certain degree. Based on the experimental results, the optimal experimental condition is concluded as applied voltage 60 V, discharge frequency 20 kHz, and minimum discharge gap 3 mm. It is anticipated that the results would serve as a good guideline to the application of hydrogen production from hydrocarbon fuels by plasma reforming onboard. • An optimized rotating GAD plasma reactor is designed for CH 4 –CO 2 reforming. • Performance comparisons of different GAD plasma reactors are made. • Experimental investigations of hydrogen production are carried out. • The effects of different characteristics on the reaction are discussed. [ABSTRACT FROM AUTHOR]

The paper relates to the investigations of a low-current discharge in a vortex airflow with the electrode configuration corresponding to classical coaxial plasmatron. The gas flow rate is varied from 0.1 to 0.3 g/s at an inner diameter of the plasmatron nozzle of 5 mm. The discharge is powered by dc voltage via a ballast resistor. Typical averaged current is changed from 0.06 to 0.15 A so that a maximum averaged power dissipated in the discharge amounts to 160 W. In these conditions, a luminous gas region at the plasmatron exit, which in most publications is associated with a plasma jet, is observed. The method for the jet diagnostics based on a usage of the additional electrodes at the plasmatron exit has been proposed. The main idea of the experiments is the elucidation of the problem whether the jet actually represents the plasma area or we have to apply the term "plasma" with care. In particular, in the case under discussion the main charged particles in the jet are electrons that are emitted from a plasma column located in the plasmatron nozzle. The model that describes the formation of electron flow in the jet has been proposed. Typical electron density in the jet estimated with a usage of the model is at a level of 109 cm−3. [ABSTRACT FROM AUTHOR]

• Plasma-catalytic reforming of mixed naphthalene and toluene was carried out using a gliding arc. • Coupling plasma with NiCo/Al2O3 catalysts enhanced the oxidation of mixed tars. • The highest toluene conversion was 95.7% when using a 7.5%Ni7.5%Co. • catalyst o The highest energy efficiency for mixed tar reforming was 40.3 g/kWh. • The presence of NiCo catalysts reduced the formation of by-products. Plasma-catalytic steam reforming of mixed tar model compounds (toluene and naphthalene) from biomass gasification has been carried out in a gliding arc discharge (GAD) plasma reactor. The influence of three catalysts (15Ni, 7.5Ni7.5Co and 15Co) on the performance of the plasma reforming of toluene and naphthalene has been evaluated including the conversion, the energy efficiency, the yield/selectivity of gaseous products and the formation of by-products. A plasma-catalysis synergy was generated when introducing the catalysts to the plasma tar reforming process. The highest toluene conversion of 95.7% and naphthalene conversion of 83.4% were achieved when the 7.5Ni7.5Co catalyst was integrated with the GAD plasma at a total tar concentration of 16.0 g/Nm3 and a discharge power of 75 W. The corresponding energy efficiency for the conversion of toluene and naphthalene was 38.0 g/kWh and 2.3 g/kWh, respectively, giving the highest total tar conversion of 95.1% and overall energy efficiency of 40.3 g/kWh. The coupling of GAD with the 7.5Ni7.5Co catalyst also showed the highest yield of H 2 (42.3%) and CO (37.3%) and the highest CO selectivity of 40.1%. In addition, the combination of the GAD plasma with 7.5Ni7.5Co reduced the carbon deposition on the catalyst surfaces and the formation of by-products in the plasma-catalytic tar reforming process. The enhanced reducibility and NiCo alloy formation of the 7.5Ni7.5Co catalyst contribute to the enhanced conversion of mixed tar compounds and the formation of the plasma-catalysis synergy in the hybrid plasma-catalytic tar reforming process. [ABSTRACT FROM AUTHOR]

• Warm plasma catalytic steam methane reforming (SMR) for distributed hydrogen production is demonstrated. • The methane conversion of 90% is achieved at total hydrogen (t -H 2) production rate of 2.7 SLM. • The energy efficiency (of CH 4 to t -H 2) of 75% and the low energy cost of 1.5 kW h/Nm3 is achieved. • The formation of C 2 H x can be suppressed by SEI and S/C at plasma zone, and completely dismissed at catalyst bed zone. Steam methane reforming (SMR) via thermal catalytic approach is one of the dominant sources of industrial hydrogen, however it proceeds with slow response and low specific productivity. Here we demonstrate a plasma catalytic SMR for distributed hydrogen production, for which warm plasma by gliding arc discharge initiates the reaction, followed by Ni-based catalyst in a heat-insulated reactor without extra heating. In terms of the plasma alone process, specific energy input (SEI), steam/CH 4 ratio (S/C) and total inlet flow rate (F t) contribute to the methane conversion. In parallel, SEI and S/C account for the decrease in C 2 H x selectivity hence the increase in selectivity of CO and CO 2 , while with F t all the selectivity is approximately constant. The reaction pathway represented by the selectivity can be influenced by SEI and S/C rather F t. To utilize the heat and active species with the reaction in plasma zone, Ni/CeO 2 /Al 2 O 3 catalyst bed is coupled. For the coupled process, the conversion approaches the thermodynamic equilibrium values, with the favorable dismissed C 2 H x selectivity thus the complete selectivity to CO and CO 2. The coupled process was maintained steady for six hours, and the methane conversion of 90% at total hydrogen (t -H 2) production rate of 2.7 SLM is achieved under optimum conditions of SEI , S/C, F t and gas hourly space velocity (GHSV) of 110 kJ/mol, 3, 3 SLM and 18,000 ml·g−1 h−1. Compared to 59% and 2.3 kW h/Nm3 of the plasma alone process, such a coupled process achieves the energy efficiency (of methane to t -H 2) of 75% and the low energy cost of 1.5 kW h/Nm3. Consequently, our approach of plasma catalytic SMR features the merits of rapid response, compact system and high specific productivity, which can be anticipated for the emerging needs of distributed hydrogen generation. [ABSTRACT FROM AUTHOR]

In this study, surface modification of a silane-crosslinked polyethylene (Si-XLPE) compound was carried out by gliding arc atmospheric plasma. Samples were exposed to the plasma for different durations and the plasma-induced alterations of the surfaces were comprehensively assessed. Surface chemistry was evaluated initially via Fourier transform infrared spectroscopy (ATR-FTIR) and energy-dispersive X-ray (EDX) analysis. Surface morphology was investigated by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). For calculating surface free energy (SFE), contact angle measurement (CAM) was performed. In order to have accurate details on the surface chemistry and morphology, X-ray photoelectron spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXRD) analysis were conducted, respectively. Results revealed that this modification method doubled the amount of atomic oxygen and nitrogen on the surface, indicating the formation of polar chemical components on the surface. Moreover, plasma could change the surface morphology considerably by selective etching and impacting on roughness. Furthermore, it was observed that the modification improved the surface crystallinity to some extent and also increased SFE drastically. Surface modification of Si-XLPE by gliding arc plasma has then proved to be an effective technique during which noticeable improvement in wettability has occurred. • Silane-crosslinked polyethylene surfaces were modified by gliding arc plasma. • Noticeable alterations were observed in surface chemistry and morphology. • Wettability of the treated surface improved remarkably in the optimum condition. • Simultaneous surface functionalization and etching occurred due to the plasma. • Selective etching happened on the surface due to the presence of resistant zones. [ABSTRACT FROM AUTHOR]

• Plasma reforming of mixed naphthalene and toluene was carried out using a gliding arc. • The presence of OH radicals enhanced the oxidation of naphthalene and toluene. • The highest conversion of mixed tar was achieved at an optimal S/C ratio of 1–1.5. • The highest energy efficiency for mixed tar reforming was 53.6 g/kWh. • Adding steam or catalyst to the plasma process reduced the formation of by-products. Non-equilibrium plasma technology provides an unconventional but promising solution for the cleaning of tar contaminated bio-syngas in biomass gasification. This work is focused on the reforming of mixed naphthalene (C 10 H 8) and toluene (C 7 H 8) as typical single ring and double ring tar model components using a gliding arc discharge (GAD) reactor. The influence of naphthalene content, steam/carbon molar ratio and discharge power on the destruction of C 10 H 8 and C 7 H 8 was evaluated to understand their effects on the tar conversion, gas yield, and the energy consumption. Adding H 2 O to the plasma process forms OH radicals, creating additional reaction routes for the step-wised oxidation of naphthalene, toluene and their fragments towards the production of CO, CO 2 , and water. The highest conversion of naphthalene and toluene (∼80% overall) was obtained when the steam/carbon molar ratio changed between 1.0 and 1.5, which was dependent on the balance between two opposite effects due to the presence of steam: positive effect of OH radicals and negative effect of electron attachment on water molecules. The highest energy efficiency (53.6 g/kWh) was obtained for the conversion of mixed tar compounds, which is by far the highest in previously reported works. CO, H 2 and C 2 H 2 were the major gases with the highest CO yield of 38.6% and H 2 yield of 39.1%. Emission spectroscopic diagnostics was employed to understand the contribution of chemically reactive species to the GAD reaction. Possible reaction pathways in the plasma reforming of mixed naphthalene and toluene were proposed based on the plasma spectroscopic diagnostics coupled with a comprehensive analysis of major gas products and condensable by-products. [ABSTRACT FROM AUTHOR]

The polypropylene (PP) strips were modified with the industrial gliding arc discharge working in air flow at 50 Hz. The experiments aimed at increased wettability and improved strength of the epoxy adhesive DP190 bond with PP. While working only in dry air, the deterioration of the plasma treatment uniformity was observed at higher treatment speeds than 100 mm/s. At the same time, the tensile strength of the adhesive bond and the atomic concentrations of O and N decreased whereas the water contact angle (WCA) measurement error increased. The fast camera measurements revealed that the PP surface was treated by the direct contact with active plasma filaments. The non-uniformity of the PP surface treatment for increased treatment speed can be explained by taking into account the stochastic character of the filament propagation direction and the characteristic time scales of the process. As an improvement of the gliding arc treatment technology a new geometry utilizing the gas cross flow was proposed with the help of gas dynamic simulations. The addition of argon cross flow led to an improvement of the treatment uniformity and, for the optimized conditions, the measured tensile strength of the adhesive bond to PP was 6.5 times higher than for the untreated PP sample. The treatments with the cross flow of argon mixed with water vapors and volatile organic compounds (VOCs), ethanol and isopropanol, did not increase the tensile strength of the adhesive joint even though the wettability was higher for the mixtures with VOCs. Since the concentration of functional groups measured by X-ray photoelectron spectroscopy was well correlated with the tensile strength of adhesive joints, WCA measurements cannot be used as the only parameter judging the success of the plasma treatment aimed at an improvement of adhesive joint strength. • High speed camera revealed long plasma filaments propagating along polymer surface. • Gas cross flow addition into the air gliding arc was proposed using gas dynamics simulations. • Argon cross flow improved the width and the uniformity of the plasma treatment. • Tensile strength of adhesive bond to polypropylene was improved up to six times. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Plasma chain catalytic reforming of methanol is demonstrated. • The energy efficiency of 91% with methanol conversion of 92% is achieved. • The hydrogen atom utilization approaches 88% (59 vol%, 4.1 SLM). • Warm plasma and two-stage catalysts in a heat-insulation reactor are coupled. Abstract Hydrogen and fuel cell technologies are being deployed to increase energy reliability and environmental performance. On-board hydrogen production via thermocatalytic reforming of liquid fuels is not a new concept, but has not been realized previously due to mismatches in rates and sizes of the necessary reactors. Here we demonstrate an advanced on-board hydrogen production by warm plasma chain catalysis for fuel-cell electric vehicles (FCEVs) with high specific productivity and transient response. Methanol, air and steam reactants as two specific feeds are fed into the reactor without soot formation and catalyst sintering. Oxidative pyrolysis reaction (OPR) by plasma, steam reforming (SR), and pyrolysis at high temperature, and SR and water gas shift (WGS) at medium temperature over catalysts occur subsequently for the coupled process. The heat with OPR is efficiently utilized by the subsequent endothermic reactions. Hydrogen selectivity of 99% (59 vol%, 4.1 SLM) with methanol conversion of 92% is achieved. The CO concentration of 7 vol% approaches the thermodynamic equilibrium value of 6.65 vol%. A fascinating match of energy efficiency of 91% (of methanol to hydrogen) and the hydrogen atom utilization of 88% is stressed. It is attributed to the chain catalysis of (oxidative) pyrolysis and WGS in sequence (as well as SR), which is initiated by warm plasma. Such a coupled process can be scaled up and used for wide applications from FCEVs and hydrogen refueling stations. [ABSTRACT FROM AUTHOR]

In this study, a cylindrical plasma generator with an axial magnetic field is constructed to obtain the magnetically stabilized gliding arc discharge (MSGAD). Using high speed photography, voltage waveform analysis and spectral diagnostics, the MSGAD physical characteristics, such as arc voltage, rotation speed, electric field, excitation/rotational temperature, etc., are investigated under different magnetic field. The experimental results reveal that as the magnetic field increases, the arc voltage, rotation speed, electric field and non-equilibrium level increase, and the MSGAD is more stable under the larger magnetic field. Additionally, carbon black nanoparticles with “crumpled paper sheet” structure are prepared by the MSGAD. The results indicate that the enhanced magnetic field can promote the transition from amorphous carbon to crystalline graphite. It is inferred that the transition is likely relevant to the rotation speed and electron energy of the arc plasma. [ABSTRACT FROM AUTHOR]

Ignition and flame stability in supersonic flow have always been the key problems of research in scramjet. In addition, ignition is difficult and the cavity flameholder is susceptible to support the flame stability under extreme conditions such as low equivalent ratio. In recent years, gliding arc plasma is recognized to expand ignition and extinction limit with lower energy consumption in the field of plasma assisted ignition due to its heating and chemical effects. In this paper, a gliding arc igniter has been designed and compared with the traditional spark plug in order to quantify the ignition ability. The igniter has the same size with the spark plug, using low-power AC gliding arc to carry out ethylene ignition test in Ma = 2.52 Ma supersonic flow. The average power of gliding arc discharge is 1199 W. A high-speed camera and CH ⁎ chemiluminescence were used to make combustion diagnosis. Founded in the same discharge period, the lean ignition limit of the gliding arc is lower than the ignition limit of the spark. The average expansion of ethylene ignition limit is 17%. The ignition process is that gliding arc continues to generate the initial flame kernels during the discharge period, but it is extinguished continuously due to the strong convection. Until generating an initial flame kernel which can successfully propagate the flame. The ignition process can be divided into four stages. It continues to generate new flame kernels in flame propagation process. Gliding arc reignites the fuel and generates the new flame kernels after forming a stable flame, appearing intermittent ignition in the cavity. The high equivalent ratio can make ignition delay time shorter, generating initial flame kernels more frequently. The heating effect of the gliding arc and reignition character make the thermal product and ethylene occur intermittent combustion more often in the cavity, increasing the area of the combustion reaction. Gliding arc plasma can achieve combustion enhancement during the flame stabilization process. The shear layer of flame thickness increased by the average of 2 mm on S-B-1 and G-B-1 conditions. Compared with the traditional spark ignition, gliding arc broaden the lean blow-off limit in different stages may be the significant reason for broadening lean ignition limit. It concludes that gliding arc makes the flame's ignition limit closer to the flame's blow-off limit. [ABSTRACT FROM AUTHOR]

In this work, we developed a portable device with low production and operation costs for generating ambient-air glow discharge (AAGD) that is transferred to the surface of flowing liquid and demonstrated its applicability to practical use in agriculture. An experiment procedure that ensured the stable treatment of various liquids was established. Additionally, it was found that humidity did not have a significant effect on the treatment process, which makes the use of the developed device possible in various locations. It was found that an L-phenylalanine solution treated with AAGD allows simultaneous 40% hydroponic radish-sprout growth promotion with a bactericidal effect. Further, scalability and practical-application possibilities in hydroponic plant growth were discussed.