Pulsed Dielectric Barrier Discharge Research Articles

Dry reforming of methane by microsecond pulsed dielectric barrier discharge plasma: Optimizing the reactor structures

Dry reforming of CH4 process can convert greenhouse gases into high-value-added fuels and chemicals with its broad application prospects in environmental protection and renewable energy. Non-thermal plasma is considered an effective alternative method because it can activate CH4 and CO2 under low temperature and atmospheric pressure. This paper is aimed to optimize the plasma-assisted dry reforming of CH4 process in a unipolar microsecond pulsed coaxial dielectric barrier discharge by investigating the effects of reactor structures. The results show that the conversions of reactants and the yields of syngas were significantly affected by the reactor structures. Specifically, a multi-stage or foil external electrode and negative polar discharge could promote CH4 and CO2 conversions, gas product yields, and energy conversion efficiencies. For different electrodes, the maximal conversions of CH4 and CO2 were 20.4% and 14.1%, with an energy conversion efficiency of 4.4% under our experimental conditions. Higher conversions, yields, and energy conversion efficiencies were obtained with lower power input when applying heat insulation measures. CH4 conversion was promoted to 27.9% with a moderate energy conversion efficiency of 3.8%, but the conversion of CO2 was only 12% when packing materials into the reactor. The results can provide specific guidance for designing plasma or plasma-catalytic dry reforming reactor.

Impact of the electrode proximity on the streamer breakdown and development of pulsed dielectric barrier discharges

The impact of the electrode proximity on the streamer breakdown and development of pulsed-driven dielectric barrier discharges (DBDs) in a single-filament arrangement has been investigated in a gas mixture of 0.1 vol% O2 in N2 at 0.6 bar and 1.0 bar. The gap distance was varied from 0.5 mm to 1.5 mm, and the applied voltage was adapted correspondingly to create comparable breakdown conditions in the gap. The development of the DBDs was recorded by an iCCD and a streak camera system, while fast electrical measurements provided insight into discharge characteristics such as the transferred charge and consumed energy. The results demonstrate that breakdown in a smaller gap is characterised by a slower streamer propagation but a significantly higher acceleration. It can therefore be concluded that the proximity of the cathode has a strong impact on the characteristics of the streamer breakdown. However, after the streamer has crossed the gap, the discharge structure in front of the anode was found to be the same independent of the actual gap distance.

Streamer dynamics and charge self‐erasing of two counter‐propagating plasmas in repetitively pulsed surface dielectric barrier discharge

The streamer dynamics and charge self-erasing of two counter-propagating plasmas generated by repetitively pulsed surface dielectric barrier discharge are investigated using electrical and optical diagnosis, and a two-dimensional fluid model. Three distinct discharge phases of primary, transitional and secondary streamers are identified in a single-pulse discharge through the time-resolved plasma images. Moreover, a merging phenomenon of the two opposing primary streamers is observed at the middle position of the discharge gap. Compared to the first pulse, a low streamer propagation velocity of the primary streamer is measured during the subsequent discharge process due to the limitation of residual surface charges left by the previous discharge. No significant differences of the transferred charge and the deposited energy are obtained in the sequential pulses at a discharge gap of 9 mm. Numerical simulations show that a reduction for the plasma intensity of the approached two primary streamers is attributed by the accumulated charge on the dielectric surface and gathered positive charges in the streamer head. Numerical and experimental studies indicate that the residual charges can be erased by the secondary streamer through the drifted electrons, namely that a phenomenon of charge self-erasing can be realized in the individual pulse.

Experimental study on the treatment of oil-based drill cutting by pulsed dielectric barrier discharge plasma at atmospheric pressure

Oil-based drilling cuttings produced in the process of oil exploration and shale gas development are harmful to the ecological environment. The emerging low-temperature plasma technology has shown potential for environmental protection. In this paper, pulsed dielectric barrier discharge (DBD) plasma was used to treat contaminated drilling cuttings at atmospheric pressure. The effect of adding active aluminium oxide (Al2O3) balls to the oil-based cuttings on the degradation rate of mineral oil was evaluated. Results showed that when the oil-based drilling cuttings were mixed with active Al2O3 balls, the highest degradation rate of mineral oil (68.1%) was achieved when the treatment time was 30 min. This rate was 41.8% higher than that obtained by DBD treatment alone. The Fourier transform infrared spectroscopy showed that the content of alkanes in the treated samples decreased significantly. The gas chromatography-mass spectrometry and ion chromatography analysis showed that formic acid, acetic acid, and other by-products were formed. The contents of C and H in the samples treated by DBD decreased. Overall, this study provides much-needed insights into the reaction mechanism and pollutant degradation process of the synergistic treatment system of pulsed DBD and active Al2O3 balls in the field of oil-based drilling cuttings treatment.

Mechanism and process of sulfamethoxazole decomposition with persulfate activated by pulse dielectric barrier discharge plasma

The present study focused on pulse dielectric barrier discharge (DBD) plasma activated persulfate (PS) for sulfamethoxazole (SMZ) degradation in water. The results showed that PS addition could enhance removal efficiency of SMZ in pulse DBD plasma system. The highest removal efficiency, kinetic constant and energy efficiency reached 93.4%, 0.084 min−1 and 0.353 g/kWh respectively with the PS dosage of 40:1 and input power of 85 W. With increase of imput power and pulse frequency, the removal efficiency of SMZ was also increased. The removal efficiency was firstly enhanced and then declined as raising duty cycle and liquid flow rate. SMZ degradation was promoted in alkaline solution conditions. Active species including ·OH, e-, ·O2–, 1O2 and ·SO- 4 play a certain role in the degradation of SMZ. The decline of O3 and enhancement of ·OH and H2O2 were found after PS addition. In process of SMZ degradation, the overall conductivity increased but pH decreased. PS addition accelerated the removal of COD and TOC. The degradation process was explored by UV–Vis spectra, three-dimensional fluorescence and LC-MS. Three degradation pathways were deduced based on the indentified intermediates. SMZ degradation in the system was considered as a toxicity-attenuation process. The water matrix including Cl-, HCO3–, SO42- and HA have some impact on SMZ degradation. This study presented that pulse DBD plasma could activate PS efficiently, which finally improved pollutant removal efficiency and energy utilization.

Plasma Surface Modification of Epoxy Polymer in Air DBD and Gliding Arc

We studied the epoxy polymer surface modification using air plasma treatment in a Gliding Arc (GA) plasma reactor and a pulsed Dielectric Barrier Discharge (DBD). We employed optical emission spectroscopy (OES) measurements to approximate the vibrational and rotational temperatures for both plasma sources, as well as surface temperature measurements with fiber optics and IR thermography to corelate with the corresponding hydrophilization of the epoxy material. Water contact angle measurements revealed a rapid hydrophilization for both plasma sources, with a slightly more pronounced effect for the air DBD treatment. Ageing studies revealed stable hydrophilicity, with water contact angle saturating at values lower than 50°, corresponding to a >50% decrease compared to the untreated epoxy polymer. ATR-FTIR spectroscopy studies showed an additional absorption band assigned to carbonyl group, with its peak intensity being higher for the DBD treated surfaces. The spectra were also correlated with the surface functionalization via the relative peak area ratio of carbonyl to oxirane and benzene related bands. According to SEM imaging, GA plasma treatment led to no apparent morphological change, contrary to DBD treatment, which resulted in nano-roughness formation. The enhanced surface oxidation as well as the nano-roughness formation on epoxy surface with the air DBD treatment were found to be responsible for the stable hydrophilization.

Characteristics of a nanosecond pulsed dielectric barrier plasma actuator with a surface water film

Aircraft icing is one of the most serious hazards for airflight operations. The nanosecond pulsed surface dielectric barrier discharge (NSDBD) plasma actuator is recognized as an extremely promising anti-icing technology. In this paper, a multi-physics coupling simulation is used to study the plasma-discharge characteristics and responses of the air–water flow field generated by an NSDBD plasma actuator with a surface water film. The computational model describes air flows through an NSDBD plasma actuator with a water film at the center of two upper powered electrodes. The multi-physics model is solved using the drift-diffusion and energy-conservation equations for the plasma discharge and the mass, momentum, energy, and concentration equations for the air–water flow. The results show that, at the beginning of the voltage pulse, the surface water film has no effect on the plasma discharge. Then, during the pulse plateau time, the film leads to a longer plasma-discharge time and a larger plasma-discharge region. Furthermore, the film causes the plasma-actuator surface to develop a virtual positive electrode that would otherwise be absent and results in the plasma actuator generating more intense shock waves, higher gas temperatures, and larger heated regions.

Highly Selective Conversion of Alkali Lignin into Aromatic Monomers by Pulse Dielectric Barrier Discharge Plasma at Mild Reaction Conditions

Highly Selective Conversion of Alkali Lignin into Aromatic Monomers by Pulse Dielectric Barrier Discharge Plasma at Mild Reaction Conditions

Experimental study on plasma actuation characteristics of nanosecond pulsed dielectric barrier discharge

Combining high-speed schlieren technology and infrared imaging technology, related research has been carried out on the influence of parameters such as actuation voltage, repetition frequency, and electrode size of an actuator on the discharge characteristics, induced flow field characteristics, and thermal characteristics of nanosecond pulsed dielectric barrier discharge. The results show that increasing the value of the actuation voltage can significantly increase the actuation intensity, and the plasma discharge area is significantly extended. Increasing the repetition frequency can increase the number of discharges per unit time. Both will cause more energy input and induce more changes in the flow field. The effect of temperature rise is more significant. The width of the covered electrode will affect the potential distribution during the discharge process, which in turn will affect the extension process of the plasma discharge filament. Under the same actuation intensity, the wider the covered electrode, the larger range the induced flow field and temperature rise is. Preliminary experimental analyses of high-frequency actuation characteristics, temperature field characteristics, flow field characteristics and actuation parameter settings provide support for the parameter selection and partial mechanism analysis of plasma anti-icing.

Ice shape modulation with nanosecond pulsed surface dielectric barrier discharge plasma actuator towards flight safety

Ice accretion on aircraft wings seriously damage the aerodynamic performance and flight safety of an aircraft. To deal with this issue, a leading-edge ice shape modulation method using nanosecond pulsed surface dielectric barrier discharge (nSDBD) is proposed, featuring the merit of less energy consumption when compared to full-wing de-icing. A set of wind tunnel experiments are conducted for verification purposes. Results show that the dangerous continuous ice can be modulated into periodically segmented ice pieces by nSDBD, forming a wavy leading edge, and the energy consumption of ice shape modulation is less than 50% of that of complete deicing. In the case of NACA0012 airfoil, ice shape modulation can improve the lift noticeably at each angle of attack (0° to 22°), delay the stall angle by 2°, and reduce the drag coefficient by more than 50% compared to full ice condition. The duration of ice shape modulation with plasma actuators lasts for about 4 min to 6 min. For flow separation control, the coherent streamwise vortices generated by the wavy leading edge are able to enhance the mixing between the boundary layer and the freestream, resulting in an increase of the ability to resist the adverse pressure gradient above the airfoil. Since both ice shape modulation and flow separation control benefit the aerodynamic performance of icing airfoils, the flight safety is improved.

Numerical Study on Mechanism and Optimization of Pulsed Discharges Without Voltage Plateau Phase

In recent years, pulsed discharges at atmospheric pressure have attracted extensive attention due to their remarkable discharge advantages. In this article, a fluid model is applied to investigate a new type of pulsed dielectric barrier discharge (DBD), characterized by a sharp rising phase and slow falling phase but without a plateau phase, which could be realized by using a circuit composed of a device called silicon diode for alternating current (SIDAC). Based on the computational data, the influences of voltage waveform on the plasma density and electric field are carefully discussed. The simulation results show that only one significant discharge event occurs during the voltage rising phase, which produces a large electron density with high electron temperature, but the secondary discharge current cannot be observed due to the slow voltage falling phase. We also qualitatively investigate the effects of discharge parameters on the plasma dynamics, such as the relative permittivity, barrier thickness, and repetitive frequency from simulation data, which agree well with the experimental observation. Based on the simulation results, the optimization of this pulsed discharges to enhance the electron density and improve the electron temperature is discussed, thus promoting the wide applications of the pulsed discharges.

Flow separation control in S-shaped ∼inlet with a nanosecond pulsed surface dielectric barrier discharge plasma actuator

A nanosecond pulsed surface dielectric barrier discharge (nSDBD) plasma actuator is proposed to eliminate the complex 3D flow separation in an S-shaped ∼engine inlet. A set of wind tunnel experiments based on pressure measurements are conducted to verify the flow control effectiveness and obtain the influence laws of actuation voltage, pulse frequency, actuator layout and coverage area. The results show that nSDBD can effectively eliminate flow separation, leading to a noticeable improvement in the total pressure distribution at the outlet, manifested as a reduction in the low-pressure zone and an extension of the high-pressure zone. The spanwise layout nSDBD delivers a better flow control effect compared to the streamwise layout. For the same geometrical layout, the flow control effect improves with increasing voltage, and the optimal actuation frequency corresponds to a Strouhal number of approximately F + = 0.5. In particular, with a spanwise array of nSDBD plasma actuators operating at V p-p = 10 kV and F + = 0.5, the flow separation region is completely suppressed. The mechanism of flow separation with nSDBD can be ascribed to the mixing enhancement between the boundary layer and the main flow, which improves the boundary layer’s ability to resist the adverse pressure gradient.

Numerical modeling and mechanism investigation of nanosecond-pulsed DBD plasma-catalytic CH4 dry reforming

Plasma-catalytic CH4 dry reforming is an emerging technology that takes advantage of plasma-catalysis interactions to implement the conversion of CH4 and CO2 into syngas and valuable chemicals. In this work, an experiment is conducted to determine the reduced electric field E/N in the numerical modeling. In addition to essential reactor parameters, catalysis characteristics are integrated into the modeling. The 3D geometry of a nanosecond (ns) pulsed DBD plasma reactor for plasma-catalytic CH4 dry reforming is reduced into a 0D kinetics model to investigate the inherent plasma-catalysis mechanisms. The simulation results indicate that C2O4 + and CH4 +, H and O, and CH4(v 13) are the dominant ions, radicals and vibrationally excited species, respectively. Although the reactions related to CH4 and CO2 consume 19.7% and 80.3% of the total electron energy, the electron energy loss caused by the CH4 ionizations (1.3%) is distinctly higher than that caused by the CO2 ionizations (0.4%). Surface reactions can generate a large amount of adsorbed species CH3(s), H(s), CO(s) and O(s). An amount of 77.2% of formaldehyde is produced by the reaction between CH3 and O. In addition, methanol is derived from the reactions between CH3 and OH in the pulsed dielectric barrier discharge (DBD) plasma catalytic reforming CH4/CO2. This numerical modeling reflects the practical plasma-catalysis system and therefore should be a novel tool to further understand the complicated underlying mechanism of the ns-pulsed DBD plasma-catalytic CH4 dry reforming.

Numerical investigation on the heterogeneous pulsed dielectric barrier discharge plasma catalysis for CO2 hydrogenation at atmospheric pressure: Effects of Ni and Cu catalysts on the selectivity conversions to CH4 and CH3OH

AbstractThe simulation model of the pulsed dielectric barrier discharge plasma catalytic CO2 hydrogenation is established to numerically investigate the effects of Ni and Cu catalysts on the selectivity conversions to CH4 and CH3OH. Under plasma without catalyst, the electron impact CO2 and CO produce CO and C, and then stepwise hydrogenations of CO and C generate CH3OH and CH4. Under plasma with Ni catalyst, Langmuir–Hinshelwood (LH) reactions mainly form the CHx(s) and Eley–Rideal (ER) reaction CH3(s) + H → CH4 are the key paths of CH4 synthesis. Under plasma with Cu catalyst, the intermediate CH3O(s) is principally produced by the LH reaction between CH2O(s) and H(s), followed by the ER reaction CH2O(s) + H → CH3O(s). While CH3OH(s) is mainly produced by the ER reaction CH3O(s) + H → CH3OH(s), CH3O(s) + H(s) → CH3OH(s) + S is a rate‐limiting step owing to the higher reaction energy barrier.

Patterned superhydrophobic surface fabrication by coupled atmospheric pressure RF and pulsed volume dielectric barrier discharges

AbstractSuperhydrophobic (SH) surfaces have great potential in numerous applications. Plasma polymerization is one of the most efficient technologies for engineering SH surfaces due to its unique feature of tailoring surface chemistry and surface topography simultaneously. Herein, a novel sandwich‐like plasma device that consists of contiguous two‐stage dielectric barrier discharges (DBDs) driven by the time‐modulated radiofrequency (RF) and pulsed power sources is proposed to polymerize hexamethyldisilazane (HMDSN) at atmospheric pressure for the purpose of SH surface engineering. The coordination of dual power sources shows effective performances in plasma operation and material surface treatment, compared to the case driven by any power source alone. Easy ignition and enhanced stability are achievable for the upper RF DBD with the assistance of the bottom pulsed DBD. Vice versa, a diffuser pulsed discharge is obtainable with the input of abundant active and energetic species and precursor fragments from the upper RF plasma. Diagnostic measurements by optical emission spectroscopy and Mie scattering demonstrate that HMDSN fragmentation and nanoparticle nucleation are initiated predominantly by the RF‐driven plasma. These species and nanoparticles are further fragmented and dispersed in the bottom pulsed discharge. Consequently, the desired SH surface is fabricated with a similar pattern to that of the pulsed DBD geometry. This study provides a new pathway based on the plasma‐assisted method to control surface hydrophobicity and provides insights on a new plasma deposition method suitable for atmospheric pressure material processing.

Tailoring the working gas flow to improve the surface modification of plasma-treated polymers

The paper aims to comparatively investigate the plasma-induced effects − under different discharge regimes: stationary and flowing gas (He and He + 0.5%O2) − on the surface properties of four types of polymers, with a distinct structure, degree of oxidation, and functionality. A pulsed dielectric barrier discharge is used to produce homogenous non-thermal atmospheric-pressure plasma for uniform, efficient, reproducible chemical surface processing. The discharge characteristics, specific to each mode of operation, were analyzed in correlation with the changes in the surface characteristics found following plasma exposure. The plasma treatment increases the surface hydrophilization of all tested polymers, regardless of the discharge mode of operation. Nevertheless, the optimum discharge regime for surface functionalization is correlated with the polymer structure and discharge characteristics. Thus, polypropylene and polystyrene present the maximum wettability in trapping gas mode, while poly(methyl methacrylate) and polysulfone, in the flowing gas mixture. The experimental results demonstrate that working in trapping gas mode is advantageous due to enhanced (>15÷40%) incorporation onto the surface of functional groups related to both oxygen and nitrogen species.

Research on Electron Evolution of Atmospheric Pressure Pulsed Dielectric Barrier Discharge Based on Two-dimensional Symmetrical Fluid Model

In recent years, plasma technology under atmospheric pressure has been widely used, and it is urgent to study the mechanism of plasma microcosmic particles. With the development of computer technology, it may be a promising method to describe the microcosmic discharge process by simulation. In this study, a two-dimensional symmetrical fluid model of ns pulse dielectric barrier discharge (DBD) at atmospheric pressure was constructed using COMSOL software. The movement behavior of electrons in different working gas, different gap distance and different electrode radius was analyzed. It was found that in helium, the electrons would move to the outside electrode area with low electron density obviously. In argon, the electrons would always be mainly constrained within the electrode area, and the electron density is more than 105 times than that of the initial value. Changing the gap distance will change the diffusion rate and maximum density of electrons. The electron distribution will be more homogeneous, and the density within the electrode area will increase 102-103 times at large gap distance. Changing the electrode diameter has little impact on electron movement behavior. The validity of the model is verified by comparing experimental and simulated voltage and current waveforms.

Reaction mechanism in non-thermal plasma enabled methane conversion: correlation between optical emission spectroscopy and gaseous products

In this work, the reaction mechanism in non-thermal plasma enabled methane conversion driven by different sources, i.e. microwave discharge, nanosecond pulsed dielectric barrier discharge, and spark discharge, is investigated. The behaviour of reactive species is monitored using the optical emission spectroscopy (OES), while the final gaseous products are analysed with gas-chromatograph. A zero-dimensional (0D) reaction kinetics model is established to reveal the underlying reaction processes. By changing pressure, different plasma modes (diffuse and filamentary) are achieved and the relative emission intensity of different species and distribution of gaseous productions are manipulated. It is found that there is a strong correlation between the intensity-ratio of C2 A → X and CH A → X, gas temperature, and the relative concentration of C2 products in different discharge forms, i.e. higher intensity ratio of C2/CH is associated with higher gas temperature and more unsaturated hydrocarbon products. Assisted with the 0D reaction kinetics model, the relationship between the intermediate species and final products is illustrated. Based on the investigation in this work, it is proposed that intensity ratio of OES can be widely adapted as a non-intrusive and real-time process monitoring in the plasma-enabled methane conversion.

Investigation of vertical tail buffeting alleviation controlled by nanosecond plasma actuators

An experimental study was conducted with the aim of alleviating the vertical tail buffeting of a 55° delta wing using pulsed nanosecond dielectric barrier discharge plasma actuators. The flow physics in the event of wing stall, flow reattachment, vortex breakdown, shear layer under plasma actuation were obtained and analyzed, and results indicate that plasma actuation promotes flow attachment and manipulates the shear layer. The acceleration results indicate that the structural response of the vertical tail increases with an increasing angle of attack, and the first bending mode response increases most significantly at the post-stall angle. Manipulation of flow field by plasma actuation produces a considerable reduction in buffeting response and mainly controls the first bending mode. The characteristics of velocity fluctuations show two important factors affecting buffeting: the redistribution of loads and the spectrum change of fluctuations, both of which are related to the movement of the impingement point of the shear layer onto the vertical tail controlled by plasma actuation. Theoretical analysis indicates that the impingement point moving downward in the vertical direction of the vertical tail under plasma actuation is the main reason for reduction of the first bending mode response.

Effect of voltage and oxygen on inactivation of E. coli and S. typhi using pulsed dielectric barrier discharge

This work presents the study of the voltage and oxygen effect on bacterial inactivation in water using a pulsed dielectric barrier discharge (DBD) under atmospheric pressure, where Escherichia coli (E. coli) and Salmonella typhi (S. typhi) bacteria were used as model microorganisms. A cylindrical DBD reactor was developed and tested in applications to assay the efficiency of bacterial inactivation in water on a volume of 500 mL flowing continuously throughout the system assisted with a peristaltic pump at 4.4 ± 0.1 mL/s. The efficiency of the treatment reached a 6-log10 reduction for both E. coli and S. typhi bacteria at 106 CFU/mL of concentration at the end of the first cycle of treatment at a minimum voltage of 12 kV with oxygen bubbling gas, concluding that there was a minimum voltage to produce inactivation of E. coli and S. typhi samples. Bacterial inactivation without the oxygen condition contrasted with the high rate of inactivation with oxygen at relatively low voltage discharges.