Glow Discharge In Air Research Articles

Experiments and Theory on Droplet Ignition with Spark Discharges

ABSTRACT Ignition experiments were performed with individual n-decane droplets, initially, about 1 mm in diameter, which were suspended in quartz fibers and subjected to electrical discharges (sparks) of controlled power and duration. Experiments were performed with glow and arc discharges in air at 1 atm and approximately 300 K . Theory is developed to predict the probability of ignition of a fuel droplet as a function of time when it is exposed to an ignition spark. The theory considers the effect of random spark-to-spark fluctuations in the heat flux into the liquid on the time for the droplet surface temperature to be high enough to enable ignition. A Bayesian analysis is also performed to evaluate confidence intervals for parameters related to droplet ignition. Reasonable agreement between theory and experiment is demonstrated, suggesting that spark-to-spark fluctuations of the heat flux into a droplet may lead to a sigmoidal variation of the probability of ignition with respect to time.

Assessing the efficacy of an atmospheric air DC glow discharge system for sustainable nitrogen fixation: a vibrational coherent anti-Stokes Raman scattering study

In addressing the substantial greenhouse gas emissions produced by the energy-intensive Haber–Bosch synthesis, this study investigates the viability of sustainable nitrogen fixation (NF) via low-temperature plasma systems energized by renewable sources. Utilizing vibrational coherent anti-Stokes Raman scattering as a diagnostic tool, we probed the nitrogen rovibrational temperature and population dynamics within a DC glow discharge in atmospheric air, a setting with considerable promise for eco-friendly fertilizer production. Besides, density for atomic N , O , and NO was quantified by laser-induced fluorescence (LIF) or two-photon absorbed LIF methods. Our findings reveal a quasi-equilibrium between rotational and vibrational energy states in the DC glow discharge environment, reaching an approximate value of 3500 K at the discharge core. The discharge parameters, discharge current, air flow rate, and discharge gap influence the rovibrational temperature, density distribution of species of interest, and the NF energy cost. However, the influences induced by these parameters are of limitations. Further analysis implies that the high gas temperature and its induced significant vibrational-rotational and vibrational-translational energy exchange are mainly responsible for the non-ideal NF energy cost.

The impact of large volume atmospheric pressure air glow discharge plasma on enhancing denim fabric (textile) sewing process

A direct-current large-volume atmospheric pressure air glow discharge plasma (APAGDP) was developed to enhance the sewing process of denim fabric. The generated plasma was characterized optically, electrically, and spectroscopically. The generated plasma presents a positive electric resistance behaviour. The plasma emission spectra are dominated by the nitrogen second positive system. Its intensity increases with the applied voltage. The generated plasma was used as a pre-treatment to enhance the sewing of the denim fabric at different exposure times, from 5 to 600 s. The scanning electron microscopy images showed no damage to the surface morphology of the denim fabric after plasma treatment. The sound pressure level (SPL) was used to verify the plasma effect on the denim fabric as compared to the untreated fabric. The SPL decreases with plasma exposure time. This result indicates that the plasma improves the sewing performance of the denim fabric.

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

The kinetics of decomposition of ibuprofen in its aqueous solution by the action of atmosphericpressure direct-current discharge in ambient air has been studied. The treated solution served as both the cathode and the anode of the discharge system. Degradation rates and effective degradation rate constants have been determined. Based on these data, the energy yields and degrees of destruction were calculated for various discharge powers (discharge currents). Discharges in a liquid cathode and anode differ little in the energy yields of degradation. But the rates and rate constants of degradation in the liquid cathode are higher than in the liquid anode. Therefore, the complete destruction of ibuprofen in the liquid cathode is achieved within shorter discharge times. A comparison is made of the destruction efficiencies for the cases of solution treatment using glow, dielectric barrier, and pulsed corona discharges.

Influence of air plasma modification power on surface properties of basalt fibers and basalt/poly(butylene succinate) adhesion

In this study, basalt fibers were treated with air glow discharge plasma at the powers of 50, 100, 200, and 300 W to investigate the influence of plasma power on fiber surface treatment and basalt/poly(butylene succinate) (PBS) adhesion. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images showed rougher fiber surfaces when the plasma power was higher than 50 W. Water absorption measurement results demonstrated that the wettability of plasma-treated groups was significantly improved. X-ray photoelectron spectroscopy (XPS) showed that the atomic ratio of O/C increased to 0.91, 1.05, 1.86, and 1.86 for the 50 W, 100 W, 200 W, and 300 W groups, respectively. Tensile testing results of single fibers showed no strength reduction after modification. Microbond pull-out test revealed an increase in the interfacial adhesion of up to 39.2 % between basalt fiber and PBS for the 300 W group. This study demonstrates that our air plasma treatment technique was effective in the modification process for improving the basalt/PBS interfacial adhesion, where the selection of appropriate plasma treatment power was critical.

In situ probing of atmospheric-pressure warm air glow discharge for nitrogen fixation by multiple laser spectroscopies

The fixation of atmospheric nitrogen into valuable compounds through reactive plasma processes has attracted intense interests due to its easy operation and compatibility with distributed renewable energy sources. However, practical implementation of plasma-assisted nitrogen fixation is hampered because of its relatively low throughput, which is dominantly limited by the unclear underlying mechanisms. In this study, effort was focused on the in situ production of key species in a DC-driven warm air glow discharge at atmospheric pressure with the help of advanced laser spectroscopic diagnostics. Laser Rayleigh scattering was applied to determine the gas temperature distribution in the discharge column. And mid-infrared quantum cascade laser absorption spectroscopy and one/two-photon absorption laser-induced fluorescence were performed on molecular nitric oxide (NO), atomic oxygen and nitrogen (O, N) for their absolute densities in the discharge. It is found that the spatial distributions of gas temperature, O and N atoms show peaks in the hot discharge center. In contrast, a hollow ‘doughnut’ shape characterized by the NO molecule was observed, particularly under conditions of high discharge current but low airflow rate. The steady-state simulation shows that the hollow pattern of NO is dominantly induced by the radial diffusion of species due to the steep spatial gradient of gas temperature in the discharge cross-section. Moreover, the reverse conversion by atomic N leads to a negative effect on the NO synthesis, especially at the discharge center where the N density and gas temperature are high. From the steady-state modeling, a similar hollow distribution of NO2 was depicted in the air glow discharge. These results demonstrate the strong dependence on atomic O for the major formation process of NO, and the importance of suppressing the reverse paths dominated by atomic N for higher NO production in the studied warm air plasma.

Volatile Organic Compound Fragmentation in the Afterglow of Pulsed Glow Discharge in Ambient Air.

Glow discharge (GD) source gained an increased level of attention in relation to the analysis of volatile organic compounds (VOCs) since past work showed that this soft ionization method allowed direct analysis of VOCs with minimal fragmentation, however, the issue of fragmentation was not previously studied in detail. The aim of the present work was to investigate the effect of discharge conditions on VOC fragmentation in the system consisting of the cell with pulsed glow discharge and a time-of-flight mass spectrometer. Ionization of VOCs of different classes (hydrocarbons, alcohols, esters, and carboxylic acids) was investigated. A copper cathode with flat geometry was used. VOCs were ionized in the afterglow of short pulse glow discharge in the air. The use of discharge afterglow significantly reduces or eliminates the effects of ionization mechanisms other than Penning process, in particular, electron ionization. This significantly reduced VOC fragmentation and provided rather low limits of detection. Specific cluster formation was observed for alcohols and esters, which may facilitate their identification.

(Invited) On Several Atmospheric Pressure Plasma Sources

In this talk, firstly, several plasma jets developed in our group are presented, including a nobble gas plasma jet for root canal treatment and four air plasma jet devices [1, 2] . Secondly, several interesting physics phenomena of plasma jets are introduced, such as the repeatability of the plasma bullet, the plasma interruption behavior, the plasma transfer dielectric phenomenon, and the appearance of multiple plasma bullet per voltage pulse [2-4] . Thirdly, the state-of-the-art on the measurement of VUV emission of atmospheric pressure air plasma is discussed and our results by using differential pumping system as EUV window are presented [5] . Fourthly , several different configurations of nonequal gap distance DBD are described [6, 7] . Finally, an atmospheric pressure glow discharge in air stabilized by a magnetic field and its application on nitrogen fixation are rep orted. Li, J. Liu, X. Lu, A large atmospheric pressure nonequilibrium open space air plasma based on a rotating electrode,P lasma Sources Sci. Technol. 29, 045015 (2020)Lu*, G. Naidis, M. Laroussi, K. Ostrikov, Guided ionization waves: Theory and experiments. Physics Reports , 540,123-166 (2014)Lu*, and Kostya (Ken) Ostrikov, Guided ionization waves: The physics of repeatability, Appl. Phys, Rev ,5, 031102 (2018)Liu, L. Nie, Y. Xian, X. Lu*, The twisted behavior of a rotating electrode atmospheric-pressure argon plasma jet, J. Phys. D: Appl. Phys. 54, 185201 (2021)F Liu, L Nie, X Lu, J Stephens and K Ostrikov, Atmospheric plasma VUV photon emission, Plasma Sources Sci. Technol. 29, 065001(2020)Li, S. Jin, Y. Xian, L. Nie, D. Liu, X. Lu*, A non-equal gap distance dielectric barrier discharge: between a wedge-shaped and a plane-shaped electrode, Plasma Sources Sci. Technol. 30, 065026 (2021)Jin, Z. Li, Y. Xian, L. Nie, X. Lu*, A non‐equal gap distance dielectric barrier discharge: Between cone‐shape and cylinder‐shape electrodes, High Voltage , 1-9 (2021)

An atmospheric pressure glow discharge in air stabilized by a magnetic field and its application on nitrogen fixation

AbstractAn atmospheric pressure glow discharge in air stabilized by a magnetic field is reported. The plasma is fixed at a position when the direction of the Lorentz force and the direction of the air flow is opposite. Under such condition, a stable glow discharge can be achieved and the plasma parameters can be independently controlled by the applied voltage, the magnetic field and the air flow rate, which is not the case for the widely used gliding arc (GA) discharge. For applied voltage of 6.5 kV, air flow rate of 2 L min−1, and magnetic field of 0.11 T perpendicular to the paper pointing outward, the discharge voltage (Vdis) and discharge current (Idis) are 1.2 kV and 49.7 mA, respectively. The rotational and vibrational temperature is about 3420 K and 4550 K, respectively. The electron density is on the order of 1014 cm−3 and the reduced electric field of plasma is about 36.9 Td, which is favorable for vibrational excitation of N2 to promote the production of NOx. As the plasma is fixed at a position, all the gas has to pass the plasma region and treated by the plasma when they are flowing, which is not the case for GA discharge where only a little percentage of gas is actually treated by the plasma. The energy cost of NOx production for the plasma stabilized by magnetic field of 0.19 T pointing outward is about 2.65 MJ mol−1, which is 41% lower than the GA discharge.

In situ quantification of NO synthesis in a warm air glow discharge by WMS-based Mid-IR QCL absorption spectroscopy

Nitric oxide (NO) is one of the most crucial products in the plasma-based nitrogen fixation process. In this work, in situ measurements were performed for quantifying the NO synthesis spatially in a warm air glow discharge, through the method of Mid-infrared quantum cascade laser absorption spectroscopy (QCL-AS). Two ro-vibrational transitions at 1900.076 cm−1 and 1900.517 cm−1 of the ground-state NO(X) were probed sensitively by the help of the wavelength modulation spectroscopy (WMS) approach to increase the signal/noise (S/N) level. The results show a decline trend of NO synthesis rate along the discharge channel from the cathode to the anode. However, from the point of energy efficiency, the cathode region is of significantly low energy efficiency of NO production. Severe disproportionality was found for the high energy consumption but low NO production in the region of cathode area, compared to that in the positive column zone. Further analysis demonstrates the high energy cost of NO production in the cathode region, is ascribed to the extremely high reduced electric field therein not selectively preferable for the processes of vibrational excitation or dissociation of N2 and O2 molecules. This drags down the overall energy efficiency of NO synthesis by this typical warm air glow discharge, particularly for the ones with short electrode gaps. Limitations of further improving the energy cost of NO synthesis by variations of the discharge operation conditions, such as discharge current or airflow rate, imply other effective manners able to tune the energy delivery selectively to the NO formation process, are sorely needed.

Surface modification and improvements of wicking properties and dyeability of grey jute-cotton blended fabrics using low-pressure glow discharge air plasma

Herein, we reported the improvements of wicking properties and dyeability of the jute-cotton blended (40:60) fabrics due to the effect of low-pressure glow discharge (LPGD) air plasma under selected exposure times. The microscopic features, functional groups, wettability, contact angles, wetting area, wicking rates, and reflectance values of the jute-cotton blended fabrics were analyzed using numerous experimental techniques. The scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques were used to investigate the morphological and compositional modifications of plasma-treated jute blended cotton fabrics. The compositional analysis confirmed various functional groups such as –OH, C–O, and COO− on the surface of jute blended cotton fabrics. The average pore radii and diffusion coefficient were calculated by using the modified Lucas-Washburn equation. The plasma-treated fabrics were shown to have an average pore radius of 0.93, 1.46, 2.26, and 4.8 μm under treatment time of 5,10,15, and 20 min. Nearly 50% reduction of contact angle was observed after a plasma treatment time of 20 min. The absorption to scattered ratio, K/S (determined using Kubel-Munk model) of the colored fabrics with 5 min pre-treated plasma was 6.47, although it was raised up to 8.51 after 20 min of pre-treatment. A reactive dye, Bezaktiv Red S–3B, was used for the dyeability test, and our findings showed that the dyeability and the wettability of the fabric were substantially enhanced with the treatment time of LPGD air plasma. Among the samples, only 10 min plasma pre-treated colored fabric exhibited a color difference of less than one compared to the standard one.

A proposed method for measurement of absolute air fluorescence yield based on high resolution optical emission spectroscopy

In this work, we present a method for absolute measurement of air fluorescence yield based on high resolution optical emission spectroscopy. The absolute measurement of the air fluorescence yield is feasible using the Cherenkov light, emitted by an electron beam simultaneously with the fluorescence light, as a “standard candle”. The separation of these two radiations can be accomplished exploiting the “dark” spectral regions of the emission band systems of the molecular spectrum of nitrogen. In these “dark” regions the net Cherenkov light can be recorded experimentally and be compared with the calculated one. The instrumentation for obtaining the nitrogen molecular spectra in high resolution and the noninvasive method for monitoring the rotational temperature of the emission process are also described. For the experimental evaluation of the molecular spectra analysis we used DC normal glow discharges in air performed in an appropriate spectral lamp considered as an air-fluorescence light emulator. The proposed method and the associated instrumentation could be tested and used in thin or thick target experiments in electron beam accelerators as a candidate optical system for this purpose.

Spectroscopic of Radicals Formed and Nitrate Production by Contact Glow Discharge Air Plasma Electrolysis

This research’s aims to determine the hydroxyl radicals formed and the production of liquid nitrate in the nitrate synthesis process using plasma electrolysis. Nitrate synthesis has been carried out by various methods including Haber Bosch nitrogen fixation. The synthesis of Haber Bosch nitrate actually causes high gas emissions and is not environmentally friendly. This has led to the synthesis of nitrate which does not cause emissions and is environmentally friendly, namely by plasma electrolysis. The methodology used in plasma electrolysis to produce liquid nitrate fertilizer, by injecting air into the tungsten anode and K2SO4 electrolyte. The hydroxyl analysis formed was carried out by looking at the IR spectrum measured using FTIR spectroscopy at an absorption band of 500 cm−1 to 4000 cm−1. Analysis of the nitrates formed was carried out using a UV-VIS spectrophotometer. The results obtained were that at t = 10 minutes OH and NH3 radicals were formed at a wavelength of 3331.47 cm-1 and 1634.63 cm-1. The nitrate produced at 0.02 M K2SO4 with an airflow rate of 0.2 lpm resulted in an optimal nitrate of 269.12 ppm with an energy consumption of 82.95 kJ/mmol and a yield of 21.7% mol.

Treatment of starch films with a glow discharge plasma in air and O2 at low pressure.

In this study, the effect of different cold plasma treatments was investigated as a novel method for the modification of starch film properties. The films were prepared from wheat starch using a solvent casting method and then treated with air and O2 glow discharge plasma at different durations (4, 8, and 12 min). A significant increase in the hydrophilicity of the films was observed due to the formation of oxygen-containing groups after plasma treatment. Fourier transform infrared analysis illustrated a decrease in C-H groups that caused an increase in C-O and C-O-C groups in air-treated films and carbonyl groups in O2-treated films. The surface roughness of the treated films increased from 17.6 nm to 22.5 and 20.6 nm after air and O2 treatments, respectively. Plasma treatments decreased oxygen permeability of the films but no significant difference in the water vapor permeability was observed. After plasma treatment, tensile strength of films was improved due to crosslinking and etching at the surface, although elongation at break remains unchanged.

Modelling of an Atmospheric–Pressure Air Glow Discharge Operating in High–Gas Temperature Regimes: The Role of the Associative Ionization Reactions Involving Excited Atoms

A model of a stationary glow-type discharge in atmospheric-pressure air operated in high-gas-temperature regimes (1000 K < Tg < 6000 K), with a focus on the role of associative ionization reactions involving N(2D,2P)-excited atoms, is developed. Thermal dissociation of vibrationally excited nitrogen molecules, as well as electronic excitation from all the vibrational levels of the nitrogen molecules, is also accounted for. The calculations show that the near-threshold associative ionization reaction, N(2D) + O(3P) → NO+ + e, is the major ionization mechanism in air at 2500 K < Tg < 4500 K while the ionization of NO molecules by electron impact is the dominant mechanism at lower gas temperatures and the high-threshold associative ionization reaction involving ground-state atoms dominates at higher temperatures. The exoergic associative ionization reaction, N(2P) + O(3P) → NO+ + e, also speeds up the ionization at the highest temperature values. The vibrational excitation of the gas significantly accelerates the production of N2(A3∑u+) molecules, which in turn increases the densities of excited N(2D,2P) atoms. Because the electron energy required for the excitation of the N2(A3∑u+) state from N2(X1∑g+, v) molecules (e.g., 6.2 eV for v = 0) is considerably lower than the ionization energy (9.27 eV) of the NO molecules, the reduced electric field begins to noticeably fall at Tg > 2500 K. The calculated plasma parameters agree with the available experimental data.

Comparative Kinetics of Changing Chemical Composition of Liquid Water Anode and Cathode of DC Glow Discharge in Air

The kinetics of the formation of nitrates, nitrite ions, and hydrogen peroxide, the products of the action of a glow discharge in air on distilled water taken as the anode of a plasma–solution system, has been first studied. A comparative analysis of the obtained experimental results with the behavior of the concentrations of products of plasma interaction with liquid cathode has been carried out. It has been shown that alternation of the polarity of the liquid electrode significantly affects the product composition and formation kinetics in the liquid phase. Qualitative explanations of the observed differences have been proposed.

Control and Stabilization of Centimeter Scale Glow Discharge in Ambient Air Using Pulse-Width Modulation

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.

Specific energy cost for nitrogen fixation as NOx using DC glow discharge in air

We report on factors influencing the specific energy costs of producing NOx from pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al2O3 catalyst powder were examined. The presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10–15 l min−1). Under these conditions, the catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200–250 GJ/tN. The transport of active chemical species and energy are likely key factors controlling the specific energy costs of NOx production in the presence of a catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.

Airglow discharge plasma treatment affects the surface structure and physical properties of zein films

Airglow discharge plasma (ADP) was used to modify the surface properties of zein film, and the influence of plasma dosage was investigated by controlling treating time (from 0s to 120s). Fourier transform infrared spectrophotometry (FT-IR) results indicated that the ADP treatment partly destroyed the acylamino groups of zein film, and the X-ray photoelectron spectrometer (XPS) analysis proved that oxygen was introduced into the matrix of zein films during ADP treatment, with the content enhanced from 14.29% to 18.45%. The microstructure of zein film exhibited a more robust surface with longer treating time, corresponding to the X-ray diffraction (XRD) results that the crystal structure of zein film was destructed under ADP treatment. The contact angle changed from 78.3° ± 2.3° to 62.1° ± 1.7° under ADP treatment, representing higher wettability. Mechanical properties also showed desirable changes under ADP treatment, with the tensile strength increased from 12.25 ± 1.23 MPa to 18.12 ± 0.68 MPa. ADP treatment could be a promising approach to modify the surface properties of protein films.