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

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

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

Made available in DSpace on 2022-04-29T08:45:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 This study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma-activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans. Laboratório de Plasmas e Processos Instituto Tecnológico de Aeronáutica (ITA) i3N Departamento de Física Universidade de Aveiro Campus Santiago Laboratório de Genoma Instituto de Ciência e Tecnologia (ICT) UNESP Division of Thoracic Surgery Instituto do Coracao Faculdade de Medicina Hospital das Clinicas HCFMUSP Universidade de Sao Paulo Faculdade de Engenharia (FEG) UNESP Laboratório de Genoma Instituto de Ciência e Tecnologia (ICT) UNESP Faculdade de Engenharia (FEG) UNESP

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

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

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

Ozone vapor, O3, is here visualized in a gliding arc discharge using photofragmentation laser-induced fluorescence. Ozone is imaged by first photodissociating the O3 molecule into an O radical and a vibrationally hot O2 fragment by a pump photon. Thereafter, the vibrationally excited O2 molecule absorbs a second (probe) photon that further transits the O2-molecule to an excited electronic state, and hence, fluorescence from the deexcitation process in the molecule can be detected. Both the photodissociation and excitation processes are achieved within one 248 nm KrF excimer laser pulse that is formed into a laser sheet and the fluorescence is imaged using an intensified CCD camera. The laser-induced signal in the vicinity of the plasma column formed by the gliding arc is confirmed to stem from O3 rather than plasma produced vibrationally hot O2. While both these products can be produced in plasmas a second laser pulse at 266 nm was utilized to separate the pump- from the probe-processes. Such arrangement allowed lifetime studies of vibrationally hot O2, which under these conditions were several orders of magnitude shorter than the lifetime of plasma-produced ozone. (Less)

International audience; Fuel cell systems for automotive applications are nowadays an important research activity. No infrastructure for distributing hydrogen still exists and the research efforts are thus focused on on-board hydrogen generation from hydrocarbon reforming. Experimental catalytic reformers have already been developed but their cost, their low time of life due to sulphur and carbon pollution problems make these reformers unusable for a commercial application. This paper presents a non-thermal gliding arc system designed to convert gasoline into hydrogen-rich gas in auto-thermal or steam reforming conditions for car application. In a first part, the chemistry of hydrocarbon reforming is briefly explained. The technology and design of the plasma reactor composed of two gliding arc in series is detailed in a second part. Finally, we demonstrate the feasibility of producing hydrogen in both auto-thermal and steam reforming conditions. The attention is focused on the influence of the different operating parameters (pressure, temperature, air and steam ratio, inlet flow rates) on the reformer efficiency and the composition of the produced gas. The experimental results are then compared to the performances of other non-thermal plasma reformers. This new plasma reformer is at its first stage of development and several technological optimisations can be performed to improve its chemical efficiency

A gliding arc in four noble gases (He, Ne, Ar, Kr) has been studied under previously unexplored conditions of varying artificial gravity, from normal 1 g gravity up to 18 g hypergravity. Significant differences, mainly the visual thickness of the plasma channel, its maximum elongation and general sensitivity to hypergravity conditions, were observed between the discharges in individual gases, resulting from their different atomic weights and related quantities, such as heat conductivity or ionisation potential. Generally, an increase of the artificial gravity level leads to a faster plasma channel movement thanks to stronger buoyant force and a decrease of maximum height reached by the channel due to more intense losses of heat and reactive species. In relation to this, an increase in current and a decrease in absorbed power was observed.