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In this work, we investigated non-equilibrium plasma produced by nanosecond repetitively pulsed glow discharges applied across a lean premixed methane-air flame. The flame is stationary, axisymmetric, and laminar. The discharges are applied on the symmetry axis crossing the reactant gases, flame front, and product gases, allowing phase-locked averaged measurements and comparisons with axisymmetric numerical simulations. The thermal effect and methyl radical production are quantified in the discharge in the reactant gas region. One-dimensional, two-beam, hybrid, femtosecond-picosecond, coherent anti-Stokes Raman scattering is used to acquire spatial and temporal profiles of temperature and oxygen-to-nitrogen concentration ratio. Photo-fragmentation laser-induced fluorescence is used to acquire quantitative two-dimensional profiles of methyl radicals in the discharge providing the first quantitative imaging of methyl produced ahead of a flame by plasma-induced methane dissociation. The spatial profiles of temperature and oxygen-to-nitrogen concentration ratio are in steady state, indicating that individual discharges have an insignificant heating effect. Upper and lower bounds of the produced mole fraction of methyl radicals in the plasma are obtained due to uncertainties in the collisional quenching rates of excited state methylidyne radicals in the plasma. The discharges produce a maximum of 600–1100 ppm of methyl radicals upstream of the flame front within 25 ns. This amount is similar to the predicted methyl mole fraction for the flame without plasma and thus represents a significant chemical perturbation to the reactants upstream of the flame front. The produced methyl follows an exponential decay in the first microsecond after the discharge with a decay constant of 8 µs close to the flame, and 0.8 µs further from the flame. The decay then deviates from the exponential curve and the methyl persists for tens of microseconds. The results suggest that for the tested configuration, the thermal effect of individual discharges through fast gas heating is negligible, while active chemical species are produced in large quantities in the reactant gases, upstream of the flame front. [ABSTRACT FROM AUTHOR]

Ammonia is gaining increasing attention as a green alternative fuel for achieving large-scale carbon emission reduction. Despite its potential technical prospects, the harsh ignition conditions and slow flame propagation speed of ammonia pose significant challenges to its application in engines. Non-equilibrium plasma has been identified as a promising method, but current research on plasma-enhanced ammonia combustion is limited and primarily focuses on ignition characteristics revealed by kinetic models. In this study, low-temperature and low-pressure chemistry in plasma-assisted ammonia oxidative pyrolysis is investigated by integrated studies of steady-state GC measurements and mathematical simulation. The detailed kinetic mechanism of NH3 decomposition in plasma-driven Ar/NH3 and Ar/NH3/O2 mixtures has been developed. The numerical model has good agreements with the experimental measurements in NH3/O2 consumption and N2/H2 generation, which demonstrates the rationality of modelling. Based on the modelling results, species density profiles, path flux and sensitivity analysis for the key plasma-produced species such as NH2, NH, H2, OH, H, O, O(1D), O2(a1Δg), O2(b1Σg+), Ar∗, H−, Ar+, NH3+, O2− in the discharge and afterglow are analyzed in detail to illustrate the effectiveness of the active species on NH3 excitation and decomposition at low temperature and relatively higher E/N values. The results revealed that NH2, NH, H as well as H2 are primarily generated through the electron collision reactions e + NH3 → e + NH2 + H, e + NH3 → e + NH + H2 and the excited-argon collision reaction Ar∗ + NH3 + H → Ar + NH2 + 2H, which will then react with highly reactive oxidative species such as O2∗, O∗, O, OH, and O2 to produce stable products of NOx and H2O. NH3 → NH is found a specific pathway for NH3 consumption with plasma assistance, which further highlights the enhanced kinetic effects.

Plasma-assisted aerosol deposition (PAD) is a new ceramic coating technology that utilizes a low-pressure induction plasma jet to accelerate particles toward the substrate and form a coating. This plasma jet was generated by a radio frequency (RF) inductively coupled plasma torch under reduced pressure. Although the particle velocity was expected to directly influence the phenomena of particle collision, adhesion, and coating formation, it has not been investigated systematically. Thus, we aimed to clarify the velocity of particles accelerated by a subsonic or supersonic low-pressure induction plasma jet using a convergent-divergent (C-D) nozzle. The particles' velocity colliding with the substrate was measured using a time-of-flight method. The effects of the C-D nozzle, input RF power, and carrier gas flow rate on the particle velocity were investigated for alumina and yttria-stabilized zirconia particles. The use of the C-D nozzle increased the particle velocity, significantly, while the input RF power was an insensitive parameter for the particle velocity. This study implies the introduction of the C-D nozzle is effective on the particle acceleration in PAD. [ABSTRACT FROM AUTHOR]

In recent years, enormous efforts have been devoted to alleviating global energy demand and the climate crisis. This has instigated the search for alternative energy sources with a reduced carbon footprint. Catalytic hydrogenation of CO2 to CH4, known as the methanation reaction, is a pathway to utilise CO2 and renewable hydrogen simultaneously. However, owing to the high stability of CO2 and thermodynamic limitations at higher temperatures, the methanation process is energy intensive. Non-thermal plasma technology has recently emerged as a promising approach to lowering the activation temperature of CO2. The application of a plasma coupled with catalytic materials allows the methanation reaction to occur at or near ambient conditions, with dielectric barrier discharges providing superior performance. The review considers the various catalytic materials applied for plasma-assisted catalytic CO2 methanation and assesses CO2 conversion, CH4 yield and fuel production efficiency obtained. The importance of reactor designs and process parameters are discussed in detail. The possible reaction pathways are considered based on in-situ and other diagnostics and modelling studies. Finally, a perspective on current barriers and opportunities for advances in non-thermal plasma technology for CO2 methanation is presented. [ABSTRACT FROM AUTHOR]

This study experimentally examines the impact of nanosecond repetitively pulsed (NRP) discharges on lean premixed methane-ammonia-air swirl flames at pressures up to 4 bar. The results reveal the extension of flame blowout limit by 10–12 % under atmospheric conditions and 5–6 % at 4 bar, when NRP discharges are applied. This decrease in the plasma effect could be attributed to the detrimental impact of strong shock waves at high pressure, destabilizing the flame. NH3-CH4-air flames shows higher lean blowout limits in comparison to CH4-air flames. NRP discharges exhibit consistent impact on the lean blowout limit enhancement across ammonia fractions (20–60 %), irrespective of pressure conditions. These results are obtained for a ratio of NRP discharge power to flame thermal power of 0.63 % and constant pulse repetition frequency of 30 kHz.

In non-equilibrium plasmas, the temperature cannot be uniquely determined unless the energy-distribution function is approximated as a Maxwell–Boltzmann distribution. To overcome this problem, we applied Tsallis statistics to determine the temperature with respect to the excited-state populations in non-equilibrium state hydrogen plasma, which enables the description of its entropy that obeys q-exponential population distribution in the non-equilibrium state. However, it is quite difficult to apply the q-exponential distribution because it is a self-consistent function that cannot be solved analytically. In this study, a self-consistent iterative scheme was adopted to calculate q-exponential distribution using the similar algorithm of the Hartree–Fock method. Results show that the excited-state population distribution based on Tsallis statistics well captures the non-equilibrium characteristics in the high-energy region, which is far from the equilibrium-Boltzmann distribution. The temperature was calculated using the partial derivative of entropy with respect to the mean energy based on Tsallis statistics and using the coefficient of q-exponential distribution. An analytical expression was derived and compared with Boltzmann statistics, and the distribution was discussed from the viewpoint of statistical physics. [ABSTRACT FROM AUTHOR]

Non-equilibrium plasma discharges can create a favorable environment for combustion processes, at low energy cost. "How favorable?" and "How low?" are two open questions that can be answered only by gaining a deep understanding of the coupling between flames and plasmas. This paper reviews recent progress in plasma-assisted combustion with a special focus on flame dynamics. First, different non-equilibrium plasma discharges are presented and their effects on flame properties are discussed. Then, an additional level of complexity is introduced by considering the effect of such plasmas on the coupling between flames and acoustic waves. While initial results suggested that the best plasma actuation would combine thermal and chemical effects, a shift towards favoring a chemical impact is emerging. Reasons for this shift are explained and future research directions are finally proposed. [ABSTRACT FROM AUTHOR]

The laser irradiation of TiH2 targets has been investigated to measure the proton energy transferred by hot non‐equilibrium plasmas in vacuum. The proton and titanium emission have been monitored by time‐of‐flight measurements to evaluate their maximum ion energy and dependence on the laser intensity. Backward and forward plasma have been generated in the range 1010–1016 W/cm2 intensity using ns and sub‐ns laser shots. Proton energy has been measured by tens eV up to about 4 MeV. The interest in proton beams generated by laser‐plasma is presented and discussed. [ABSTRACT FROM AUTHOR]

The present study evaluates the antimicrobial potential of non-equilibrium plasma against microorganisms isolated from diatomaceous earth, which is a waste product from the beer filtration process. For evaluation, waste diatomaceous earth from an industrial brewery was treated with non-equilibrium plasma using a glidearc reactor. The temperature of the treated samples was monitored. The effect of plasma on the morphology of the treated material was investigated microscopically. Plasma can affect the treated material in various ways and change its physicochemical properties. Consequently, the scope of potential plasma applications is constantly expanding from material technologies to decontamination applications in the food industry, environmental protection and medicine and stimulates activities in, for example, agriculture and medicine. At the same time, microbiological analyzes were carried out to determine the presence of selected groups of microorganisms on diatomaceous earth before and after plasma treatment. The study revealed that the porous structure of diatomaceous earth is not an obstacle to the effective removal of microorganisms from it using plasma. A significant decrease in the amount of both bacteria and yeast relative to the control (non-plasma samples) was observed with the increasing contact time of the diatomaceous earth with the plasma. The numbers of bacteria and yeast decreased by a maximum of 2.2 log10 CFU∙g−1 and 1.72 log10 CFU∙g−1 (30 min of plasma contact), respectively. The obtained results are extremely promising and encourage further, in-depth research to optimize the plasma process and its effect on microorganisms. [ABSTRACT FROM AUTHOR]

In this letter, an annular anode is designed for producing arc plasmas with a large non-equilibrium region by using a counterflow cold gas through the annular anode. The coupled mass-momentum-energy exchange processes in an argon arc plasma are studied numerically and experimentally. The counter-injection of the cold argon gas from the center of the anode leads to a steep gradient of the heavy-particle temperature due to the formation of a thin stagnation layer resulting from the interaction of the high temperature plasma with the cold gas; and in particular, a large volume non-equilibrium 'dark' plasma region is obtained above the anode surface. The results show that, with the enhancement of the convective heat transfer process in the plasma core region, the fraction of the non-equilibrium region to the whole arc plasma region reaches 92.2% where the heavy-particle temperature can be reduced significantly, e.g. ∼2300 K, while simultaneously, the electron temperature and number density are remained at high levels greater than 8000 K and 2.4 × 1020 m−3, respectively, under the operating condition studied in this letter. This research not only deepens the understanding to the non-equilibrium synergistic transport mechanisms of arc plasmas, but also provides a method for producing a large volume non-equilibrium plasma region so as to promote various existing applications, or even creating new applications in the future. [ABSTRACT FROM AUTHOR]

Electron temperature is reconsidered for weakly-ionized oxygen and nitrogen plasmas with its discharge pressure of a few hundred Pa, with its electron density of the order of 10 17 m − 3 and in a state of non-equilibrium, based on thermodynamics and statistical physics. The relationship between entropy and electron mean energy is focused on based on the electron energy distribution function (EEDF) calculated with the integro-differential Boltzmann equation for a given reduced electric field E / N . When the Boltzmann equation is solved, chemical kinetic equations are also simultaneously solved to determine essential excited species for the oxygen plasma, while vibrationally excited populations are solved for the nitrogen plasma, since the EEDF should be self-consistently found with the densities of collision counterparts of electrons. Next, the electron mean energy U and entropy S are calculated with the self-consistent EEDF obtained, where the entropy is calculated with the Gibbs's formula. Then, the "statistical" electron temperature T e st is calculated as T e st = [ ∂ S / ∂ U ] − 1 . The difference between T e st and the electron kinetic temperature T e kin is discussed, which is defined as [ 2 / (3 k) ] times of the mean electron energy U = 〈 ϵ 〉 , as well as the temperature given as a slope of the EEDF for each value of E / N from the viewpoint of statistical physics as well as of elementary processes in the oxygen or nitrogen plasma. [ABSTRACT FROM AUTHOR]

Machine learning (ML) is a set of computational tools that can analyze and utilize large amounts of data for many different purposes. Recent breakthroughs in ML and artificial intelligence largely enabled by advances in computing power and parallel computing present cross-disciplinary research opportunities to exploit some of these techniques in the field of non-equilibrium plasma (NEP) studies. This paper presents our perspectives on how ML can potentially transform modeling and simulation, real-time monitoring, and control of NEP.

Plasma methods are often employed for the desired wettability and soaking properties of polymeric textiles, but the exact mechanisms involved in plasma–textile interactions are yet to be discovered. This review presents the fundamentals of plasma penetration into textiles and illustrates mechanisms that lead to the appropriate surface finish of fibers inside the textile. The crucial relations are provided, and the different concepts of low-pressure and atmospheric-pressure discharges useful for the modification of textile's properties are explained. The atmospheric-pressure plasma sustained in the form of numerous stochastical streamers will penetrate textiles of reasonable porosity, so the reactive species useful for the functionalization of fibers deep inside the textile will be created inside the textile. Low-pressure plasmas sustained at reasonable discharge power will not penetrate into the textile, so the depth of the modified textile is limited by the diffusion of reactive species. Since the charged particles neutralize on the textile surface, the neutral species will functionalize the fibers deep inside the textile when low-pressure plasma is chosen for the treatment of textiles. [ABSTRACT FROM AUTHOR]

In this research, a type of gram negative bacteria was exposed to non-thermal plasma at a distance of (2 and 3 cm) from the plasma flow nozzle, with the use of an alternating power supply (5KHz), where exposure was made at two different voltages (4.9 and 8 kV). A negative gram of Pseudomonas aeruginosa bacteria was isolated and exposed to non-thermal plasma at different flow rates of argon gas whose value ranged from (1-5) liters/minute. The results showed that bacterial killing rate is directly proportional to distance while exposing the samples to nonthermal plasma, and the best factors by which a complete killing rate was obtained were at a distance of 2 cm with a voltage of 8 kV and a gas flow rate of 5 liters/min, while complete killing of bacteria was not achieved at a distance of 3 cm where the percentage was 95% at the same argon gas flow rate. [ABSTRACT FROM AUTHOR]

In non-equilibrium plasmas, the temperature cannot be uniquely determined unless the energy-distribution function is approximated as a Maxwell–Boltzmann distribution. To overcome this problem, we applied Tsallis statistics to determine the temperature with respect to the excited-state populations in non-equilibrium state hydrogen plasma, which enables the description of its entropy that obeys q-exponential population distribution in the non-equilibrium state. However, it is quite difficult to apply the q-exponential distribution because it is a self-consistent function that cannot be solved analytically. In this study, a self-consistent iterative scheme was adopted to calculate q-exponential distribution using the similar algorithm of the Hartree–Fock method. Results show that the excited-state population distribution based on Tsallis statistics well captures the non-equilibrium characteristics in the high-energy region, which is far from the equilibrium-Boltzmann distribution. The temperature was calculated using the partial derivative of entropy with respect to the mean energy based on Tsallis statistics and using the coefficient of q-exponential distribution. An analytical expression was derived and compared with Boltzmann statistics, and the distribution was discussed from the viewpoint of statistical physics.

Numerical results of plasma supported deflagration to detonation transition have been presented. The mathematical model includes Reynolds averaged Navier-Stokes equations for the compressible medium, enthalpy equation, the standard k- ω turbulence model, transport equations for the progress variable and flame wrinkling factor. Non-equilibrium plasma was modeled as a source of radicals. Initial concentrations of radicals were taken from the detailed plasma simulation using a three-temperature plasma model. To model equilibrium plasma we used a Joule heating source with the conductivity depending on the energy deposition time. Simulations showed that the injection of radicals was more efficient than a thermal effect of plasma in the deflagration to detonation transition time and distance. We observed changes in the detonation cell size and improvement of the detonation structure stability with the plasma addition. Because the oxygen atoms injection primarily controls the phenomenon, the detonation cell size depends on the oxygen atoms concentration and on the orientation of the plasma energy spot with respect to the detonation wave. [ABSTRACT FROM AUTHOR]

Water purification by non-equilibrium atmospheric pressure plasma has attracted much attention and is expected to be a next-generation method. However, general approaches to improve the energy efficiency of the water purification have not been revealed. Therefore, to investigate important factors for increasing its energy efficiency, we developed coaxial cylindrical plasma reactors where pulsed streamers were generated between a high-voltage electrode and running water film. To evaluate the performance of the plasma reactors, we measured hydroxyl (OH) radicals in solution based on a chemical probe method using disodium terephthalic acid (NaTA) and decolorized indigo carmine solution. Our experimental results showed that the production rate of the OH radicals was approximately 20 nmol/s and that the energy efficiency of the decolorization was on the order of 10 g/kWh. In addition, we found that controlling liquid flow based on the Coandă effect and introducing the intermittent operation of the streamer discharges to use post-discharge reactions increased the energy efficiency by a factor of approximately 3.5, which indicated that these approaches are effective to improve the performance of the water purification by plasma. [ABSTRACT FROM AUTHOR]

While polymer flooding improves oilfield recovery, it also produces a large amount of polyacrylamide wastewater (PAM). Polyacrylamide wastewater has the characteristics of a high degree of emulsification, high viscosity, and difficulty degrading. The treatment of polymer-containing sewage has become a research hotspot. In this paper, based on the dielectric barrier discharge (DBD) experiment, the effect of non-equilibrium plasma on the degradation rate and viscosity of PAM solution was studied by changing the discharge time, discharge voltage, and PAM solution concentration. At the same time, the environmental scanning electron microscopy was used to observe the PAM before and after discharge. As the morphology of the solution changed, the degradation products of PAM solution after discharge were detected by Fourier-transform infrared absorption spectrometer. The results show that under the conditions of a discharge voltage of 20 kV and a frequency of 10 kHz, the degradation rate of DBD to a PAM solution with a concentration of 1,000 mg/L can reach up to 89%. DBD can cause the PAM molecular chain to curl up and reduce its viscosity rapidly. DBD is produced as the active substance first broke the PAM macromolecular chain into small molecules. Further treatment can produce acrylamide monomer and acrylic acid. [ABSTRACT FROM AUTHOR]

The present study evaluates the antimicrobial potential of non-equilibrium plasma against microorganisms isolated from diatomaceous earth, which is a waste product from the beer filtration process. For evaluation, waste diatomaceous earth from an industrial brewery was treated with non-equilibrium plasma using a glidearc reactor. The temperature of the treated samples was monitored. The effect of plasma on the morphology of the treated material was investigated microscopically. Plasma can affect the treated material in various ways and change its physicochemical properties. Consequently, the scope of potential plasma applications is constantly expanding from material technologies to decontamination applications in the food industry, environmental protection and medicine and stimulates activities in, for example, agriculture and medicine. At the same time, microbiological analyzes were carried out to determine the presence of selected groups of microorganisms on diatomaceous earth before and after plasma treatment. The study revealed that the porous structure of diatomaceous earth is not an obstacle to the effective removal of microorganisms from it using plasma. A significant decrease in the amount of both bacteria and yeast relative to the control (non-plasma samples) was observed with the increasing contact time of the diatomaceous earth with the plasma. The numbers of bacteria and yeast decreased by a maximum of 2.2 log10 CFU∙g−1 and 1.72 log10 CFU∙g−1 (30 min of plasma contact), respectively. The obtained results are extremely promising and encourage further, in-depth research to optimize the plasma process and its effect on microorganisms.

Electron temperature is reconsidered for weakly-ionized oxygen and nitrogen plasmas with its discharge pressure of a few hundred Pa, with its electron density of the order of 1017m−3 and in a state of non-equilibrium, based on thermodynamics and statistical physics. The relationship between entropy and electron mean energy is focused on based on the electron energy distribution function (EEDF) calculated with the integro-differential Boltzmann equation for a given reduced electric field E/N. When the Boltzmann equation is solved, chemical kinetic equations are also simultaneously solved to determine essential excited species for the oxygen plasma, while vibrationally excited populations are solved for the nitrogen plasma, since the EEDF should be self-consistently found with the densities of collision counterparts of electrons. Next, the electron mean energy U and entropy S are calculated with the self-consistent EEDF obtained, where the entropy is calculated with the Gibbs’s formula. Then, the “statistical” electron temperature Test is calculated as Test=[∂S/∂U]−1. The difference between Test and the electron kinetic temperature Tekin is discussed, which is defined as [2/(3k)] times of the mean electron energy U=⟨ϵ⟩, as well as the temperature given as a slope of the EEDF for each value of E/N from the viewpoint of statistical physics as well as of elementary processes in the oxygen or nitrogen plasma.

Angularly resolved X-ray scattering measurements from fs-laser heated hydrogen have been used to determine the equilibration of electron and ion temperatures in the warm dense matter regime. The relaxation of rapidly heated cryogenic hydrogen is visualized using 5.5 keV X-ray pulses from the Linac Coherent Light (LCLS) source in a 1 Hz repetition rate pump-probe setting. We demonstrate that the electron-ion energy transfer is faster than quasi-classical Landau-Spitzer models that use ad hoc cutoffs in the Coulomb logarithm.

Plasma-liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

Plasma methods are often employed for the desired wettability and soaking properties of polymeric textiles, but the exact mechanisms involved in plasma–textile interactions are yet to be discovered. This review presents the fundamentals of plasma penetration into textiles and illustrates mechanisms that lead to the appropriate surface finish of fibers inside the textile. The crucial relations are provided, and the different concepts of low-pressure and atmospheric-pressure discharges useful for the modification of textile’s properties are explained. The atmospheric-pressure plasma sustained in the form of numerous stochastical streamers will penetrate textiles of reasonable porosity, so the reactive species useful for the functionalization of fibers deep inside the textile will be created inside the textile. Low-pressure plasmas sustained at reasonable discharge power will not penetrate into the textile, so the depth of the modified textile is limited by the diffusion of reactive species. Since the charged particles neutralize on the textile surface, the neutral species will functionalize the fibers deep inside the textile when low-pressure plasma is chosen for the treatment of textiles.

Zero-dimensional computations of nanosecond-order ignition using a nanosecond discharge are performed with two constraints. The effects of these constraints are assessed to study the experimental rapid pressure change properly at the initial stages. The computations are carried out with the following constraints: constant internal energy and volume (U&V) and constant enthalpy and pressure (H&P), revealing differences between the two solutions. As the pressure remains constant under the H&P constraint, the total number density of all species decreases during ignition. In this case, O radicals are less generated and consumed. The progression of all reactions and temperatures increases under the H&P constraint less intensely than under the U&V constraint. Significant differences are found between the results calculated under the U&V and H&P constraints. Therefore, large discrepancies with real phenomena can be caused if the loss due to pressure reduction is not treated well. [ABSTRACT FROM AUTHOR]

• The introduction of plasma enhances the decomposition of ammonia. • The existence of diluted gas is favorable for plasma discharge. • Argon is the most readily ionized gas in discharge process. • The ammonia conversion increase with the increase of pulse voltage and frequency. Ammonia, which can serve as a hydrogen carrier for later dehydrogenation in zero-carbon hydrogen generation, is considered one of the key solutions. However, this solution is challenged by the high decomposition temperature and low reaction efficiency. In this paper, non-equilibrium plasma was used to effectively improve the reaction performance of ammonia decomposition to hydrogen and nitrogen using a dielectric barrier discharge reactor. Impacts of operating conditions including discharge parameters, diluted gases, and ammonia concentration on hydrogen generation were investigated. The ammonia decomposition breakdown voltage followed the order of 1 % ammonia/carbon dioxide (4000 V) > 1 % ammonia/nitrogen (3500 V) > 1 % ammonia/helium (1500 V) ≈ 1 % ammonia/argon (1500 V). The effect of pulse voltage and frequency is more significant on plasma-assisted ammonia decomposition compared to the pulse width. When the pulse frequency and width were 30 kHz and 100 ns at 298 K, the ammonia conversion reached 26.3 %, 34.1 % and 40.9 % at 5000, 7000, and 10000 V, respectively. With the addition of argon in 5 % ammonia/helium, the resulting penning effect makes the discharge easier and more uniform to promote ammonia decomposition. Furthermore, the kinetic analysis was investigated to better understand the conversion and utilization of ammonia in plasma-assisted reactions. [ABSTRACT FROM AUTHOR]

• A skeletal plasma kinetic mechanism of CH 4 /O 2 /He with good performance in predicting PAI for modeling SDBD is developed. • Sequential electric field is used to model effects of PRF on low temperature ignition of stoichiometric and lean CH 4 /O 2 /He mixture. • The plasma-assisted ignition of lean CH 4 /O 2 /He mixture is induced by accumulations of more short lifetime species via increasing PRF. A nanosecond repetitive pulsed surface dielectric barrier discharge (NRP-SDBD) is a promising method for generation of non-equilibrium plasma with more kinetic activity. This paper presents numerical studies on the effects of pulse repetition frequency (PRF) on low temperature ignition of lean and stoichiometric CH 4 /O 2 /He mixture in NRP-SDBD plasma. A skeletal plasma kinetics mechanism is primary developed and calibrated, to mitigate the computational loads of modeling SDBD discharge by the two-dimensional plasma solver PASSKEy coupled with Poisson's equation. The discharge current was well predicted, meanwhile the sequential and spatial reduced electric field (E/N) is revealed as the ionization wave propagates forward. Special attention is placed on time-evolution of electric field strength used as inputs in simulation of plasma assisted ignition (PAI) conducted by zero-dimensional ZDPlasKin-CHEMKIN code. The principle of PAI on lean and stoichiometric CH 4 /O 2 /He mixture via varied PRF is analyzed in details from view of plasma kinetics and chemical kinetics. Ultimately, the important role of plasma active species O, O(1D), O 2 (a1Δ g) on promoting ignition chain reactions is highlighted. It is also concluded that high PRF is beneficial for the accumulation of short lifetime species such as CH 4 (v13) and O(1D), which participate in the formation of important intermediate CH 3. [ABSTRACT FROM AUTHOR]

It has been demonstrated by a large number of studies that microwave ignition can greatly extend the lean-burn limit in the internal combustion engines. This paper investigates the influence of the pulse period and duty cycle of pulsed microwave signals on the combustion performance of CH4-air mixtures during microwave ignition in a constant-volume combustion chamber for a lean-burn equivalence ratio $\varphi =0.6$ and the same energy input as for conventional spark ignition. Combustion performance was evaluated with respect to combustion pressure, lean-burn limit, OH concentration, initial flame kernel, and composition of combustion emissions. The results indicate that the duty cycle (i.e. average power) strongly influences the formation and development of the initial microwave discharge, while the pulsewidth influences the generation of non-equilibrium plasma which contributes to sustained combustion. The increasing the duty cycle can improve the ignition success rate, extend the lean-burn limit, and reduce the flame development time. Moderately increasing pulsewidth can further extend the lean-burn limit, particularly for elevated initial pressures.

Water purification by non-equilibrium atmospheric pressure plasma has attracted much attention and is expected to be a next-generation method. However, general approaches to improve the energy efficiency of the water purification have not been revealed. Therefore, to investigate important factors for increasing its energy efficiency, we developed coaxial cylindrical plasma reactors where pulsed streamers were generated between a high-voltage electrode and running water film. To evaluate the performance of the plasma reactors, we measured hydroxyl (OH) radicals in solution based on a chemical probe method using disodium terephthalic acid (NaTA) and decolorized indigo carmine solution. Our experimental results showed that the production rate of the OH radicals was approximately 20 nmol/s and that the energy efficiency of the decolorization was on the order of 10 g/kWh. In addition, we found that controlling liquid flow based on the Coandă effect and introducing the intermittent operation of the streamer discharges to use post-discharge reactions increased the energy efficiency by a factor of approximately 3.5, which indicated that these approaches are effective to improve the performance of the water purification by plasma.

The paper includes the statistics of liver abscesses, etiology and related features of the diseases. The most common methods of conservative and surgical treatment of liver abscesses, currently used in surgical clinics of the Russian Federation, are presented. A small historical excursus about the existed methods of treatment is given in the paper. A comparative analysis of the currently used methods, their advantages and disadvantages is carried out. Some possible criteria for a certain method of treatment of liver abscesses are listed as well.

This paper describes the behaviour of the plasma parameters of microarcs generated between a cooled copper anode and a ceriated tungsten cathode by means of a one‐dimensional unified non‐equilibrium model for gap lengths between 15 and 200 μm and current densities from 2 × 105 up to 106 A/m2. The results obtained show that the decrease of the gap length to a few tens of micrometres for a given current density results in a progressive shrinking of the quasi‐neutral bulk in the microplasma and its complete disappearance. The decrease of the gap length further leads to an increase of the discharge voltage and the electron temperature and to slightly less heating of the gas. [ABSTRACT FROM AUTHOR]

This numerical study of the ignition characteristics of ammonia in a pulsed plasma discharge includes the assembly of a kinetic model for the oxidation of ammonia/oxygen/helium mixtures under a plasma discharge. The model was used to perform a series of simulations under varying pulsed discharge frequencies and pulse numbers, at atmospheric pressure and moderate to high temperatures (600–1500 K). A zero-dimensional solver which combines the ZDPlasKin and CHEMKIN software is used to explore the effect of pulse number and frequency on ignition delay time. For a moderate amount of pulses, a reduction of 40–60% in ignition delay time is achieved, with higher pulse repetition frequencies (PRFs) yielding shorter ignition delay times. Analysis of OH radical time evolution reveals that high PRFs support an increasing radical pool at low temperatures, whereas at lower PRFs radicals recombine in between pulses. In the thermal runaway phase, the radicals formed in conventional chain branching events are prevalent, so that OH formed in later pulses has little effect. When looking low temperatures and high PRFs, higher pulse frequencies allow for lower initial temperatures which will result in ignition. At a high enough frequency, the hysteresis of ignition and extinction is altered due to a high amount of radicals supplied and sustained by the plasma, so that there is a smooth transition and reactions at all temperatures. [ABSTRACT FROM AUTHOR]

This paper reports on an experimental investigation of the chemical impact of nanosecond repetitively pulsed (NRP) glow discharges on a laminar methane-air flame. The chosen configuration was a lean wall stabilized flame where NRP discharges were generated across the flame front. After careful selection of the excitation lines, planar laser induced fluorescence of OH and CH was conducted. Comparisons between the OH and CH fluorescence of a base flame (without plasma actuation), and those obtained during the steady state and the transient regimes of plasma actuation, were performed. First it is shown that during the steady state regime, the intensity of OH and CH fluorescence in the flame could be increased by up to 40% and 10%, respectively. In addition, the life time of OH fluorescence in the discharge channel was estimated to be between 3 and 4.5 µs. The transient regime at the beginning of plasma actuation showed that the flame began to be affected by the discharges long before OH fluorescence could be detected in the discharge channel, upstream of the flame. After 40 ms of plasma actuation, OH intensity began to increase simultaneously in both the flame and the discharge area. Based on current knowledge of nanosecond discharge chemistry, explanations for these results are proposed. [ABSTRACT FROM AUTHOR]

Plasma-Assisted Combustion (PAC) has shown potential in improving the ignition, extinction, and dynamic performance of combustion systems. In this work, nanosecond repetitively pulsed (NRP) spark discharges are applied to extend the lean blow out (LBO) limit of the SICCA-Spray burner. This laboratory-scale atmospheric test rig is equipped with a swirl spray injector representing in an idealized fashion a single sector of a gas turbine. Three fuels and injection conditions are considered: perfectly premixed methane–air, liquid heptane, and liquid dodecane injected as hollow cone sprays. The optimal electrode position that extends the LBO limit is found to be near the external edge of the outer recirculation zone (ORZ). Spectroscopic measurements show that the NRP sparks produce atomic species and heat the gas above the adiabatic flame temperature. High-speed chemiluminescence images of blow out sequences indicate that the flame evolves similarly for all three fuels from "M" or "V" shapes prevailing at ϕ = 0.9 to a configuration where chemical conversion also takes place in the ORZ at ϕ = 0.63. A low frequency combustion oscillation arises near the LBO limit (ϕ = 0.57). Spray flames blow out at this point, while the plasma-assisted ones continue to burn. It is shown that PAC provides a significant improvement of the extinction performance, in particular when operating with liquid fuel spray injection. [ABSTRACT FROM AUTHOR]

The ignition of methane/air and ethylene/air mixtures by nanosecond pulsed discharges (NSPD) is investigated numerically using a zero-dimensional isochoric adiabatic reactor. A combustion kinetics model is coupled with a non-equilibrium plasma mechanism, which features vibrational and electronic excitation, dissociation, and ionization of neutral particles (O 2 and N 2) via electron impact. A time to ignition metric τ is defined, and ignition simulations encompassing a wide range of pressures (0.5–30 atm) and pulsing conditions for each fuel are executed. For each fuel, it is found that τ depends primarily on initial pressure and energy deposition rate, and scaling laws are derived. In order to quantify the benefit gained from plasma-assisted ignition (PAI), τ is compared with a thermal ignition time. It is found that for both fuels, PAI leads to a faster ignition at low pressures, while at higher pressures (p 0 ≥ 5 atm), methane/air ignition becomes inefficient (meaning a longer ignition time for the same input energy compared to thermal ignition). Ethylene/air PAI shows only a modest deterioration. The drop in performance with pressure is found to be due to the mean electron energy achieved during the pulse, which shows an inverse relationship with pressure, leading to fewer excited species and combustion radicals. The poor performance of methane/air mixture ignition at high pressure is explained by an analysis of the reaction pathways. At high pressures (p 0 ∼ 30 atm), H is consumed mostly to form hydroperoxyl (HO 2), leading to a bottleneck in the formation of formyl (HCO) from formaldehyde (CH 2 O). Instead, for ethylene/air ignition, at both low and high pressures there exist several bypass pathways that facilitate the formation of HCO and CO directly from various intermediates, explaining the more robust performance of PAI for ethylene at pressure. [ABSTRACT FROM AUTHOR]

This study investigates the plasma properties and chemical kinetics of plasma-assisted methane reforming in a He diluted nanosecond-pulsed plane-to-plane dielectric barrier discharge (ns-DBD) through the combination of time-resolved in situ laser diagnostics and a 1-D numerical model. Plasma-assisted fuel reforming kinetic mechanisms have predominantly been evaluated on the basis of matching reactant conversion and syngas production to steady-state measurements, which cannot describe the full range of chemistry and physics necessary to validate the model. It was found that adding 1% CH 4 to a pure He ns-DBD led to a faster breakdown along the rising edge of the applied voltage pulse, thereby lowering the reduced electric field (E/N), electron number density, and electron temperature. Further addition of CH 4 did not continue to alter the E/N in the model. Laser absorption spectroscopy was used to measure gas temperature, C 2 H 2 , H 2 O, and CH 2 O in a CH 4 /CO 2 /He discharge to serve as validation targets for the predicted reaction pathways. CH 2 O was predicted within 25% of the measured value, while H 2 O and C 2 H 2 were under-predicted by a factor of two and three, respectively. From path flux analysis, the major pathway for CH 2 O formation was through the reaction between CH 3 and O, while C 2 H 2 formation had multi-step pathways that relied on ions like CH 3 + and C 2 H 5 +. The path flux analysis also shows that CH 2 is a significant intermediate for production of both CH 2 O and C 2 H 2 , and increased CH 2 concentration could improve model predictions. The results show that the use of reaction rate constants with lower uncertainties and inclusion of He 2 + are needed to improve the predictions. Finally, varying the "equivalence ratio", defined by the CH 4 dry reforming reaction to H 2 and CO, from 0.5 to 2 was shown to have a weak effect on measured product species and experimental trends were explained based on pathways extracted from the model. [ABSTRACT FROM AUTHOR]

Gliding discharge and coupled plasma-catalytic system were used for toluene conversion in a gas composition such as the one obtained during pyrolysis of biomass. The chosen catalyst was G-0117, which is an industrial catalyst for methane conversion manufactured by INS Pulawy (Poland). The effects of discharge power, initial concentration of toluene, gas flow rate and the presence of the bed of the G-0117 catalyst on the conversion of C7H8, a model tars compounds were investigated. Conversion of coluene increases with discharge power and the highest one was noted in the coupled plasma-catalytic system. It was higher than that in the homogeneous system of gliding discharge. When applying a reactor with reduced G-0117 and CO (0.15 mol%), CO2 (0.15 mol%), H2 (0.30 mol%), N2 (0.40 mol%), 4000 ppm of toluene and gas flow rate of 1.5 Nm3/h, the conversion of toluene was higher than 99%. In the coupled plasma-catalytic system with G-0117 methanation of carbon oxides was observed.

The ignition delay and NO emission characteristics of the NH 3 /N 2 /O 2 mixture under the influence of pulse–DC hybrid plasma discharges have been studied. The plasma and combustion chemistry mechanisms for NH 3 /N 2 /O 2 mixture are reviewed, an improved kinetics mechanism is proposed with a well validated electron scattering cross section data. An improved coupled plasma and combustion chemistry code allowing sensitivity/pathway analysis is developed. The role of key species on the ignition delay time and the effects of low E/N discharge over long periods of time (DC stage) on NO x emission are studied. The results show that, NO emission will be strongly enhanced due to the increased HNO, NH and N density in NH 3 containing mixtures in the DC stage, NO density increases with the E/N value in DC stage due to the reduction of NH and NH 2 species. The role of O 2 (a 1 Δ g) in promoting ignition was studied using different rate constant of O 2 (a 1 Δ g) + NO → O 2 + NO : O 2 (a 1 Δ g) mainly reacts with H 2 and H to produce radicals such as O, H and OH instead of quenched by NO. The vibrationally excited NH 3 (v2) molecule plays the dominating role in heat release through V–T relaxation with NH 3. [ABSTRACT FROM AUTHOR]