DC Corona Research Articles

Enhanced sensitivity digital holographic interferometry

Corona discharges are generally characterized by a low optical density whose detection is often near or under the limits of interferometric techniques. In this paper, we propose a method of digital holographic interferometry that enables detection with enhanced sensitivity. This sensitivity increase is obtained by post-processing the digital holographic recordings with a set of point-wise image operations. The procedure is described mathematically and illustrated experimentally. Examples are given for an opaque object and for DC corona discharges generated in the symmetrical point-plane geometry.

Enhancement of NOx abatement by advancing initiation of C3H6 oxidation chemistry with a corona radical shower

It is well known that propylene plays a very important role in decreasing the energy consumption of plasma abatement of flue gas containing NOx, but how to further improve the utilization efficiency of C3H6 needs to be studied. This paper presents an improved wire-plate type discharge reactor for plasma remediation of flue gas of utility or boiler facilities, in which nozzle electrodes for injection of additives such as C3H6 and NH3 were installed in the front of wire electrodes. This paper mainly focused on the study of advancing initiation of C3H6 oxidation chemistry and thus NO abatement by a pulsed and dc corona radical shower. The experimental results indicate that the NO removal rate was increased by over 10% with a pulsed corona radical shower; a dc corona C3H6 radical shower could increase the NO removal rate by 7%–24% under an energy-cost of 0.09–0.355 Wh Nm−3. Water vapour or ammonia injection decreased the NO abatement with the corona C3H6 radical shower, but the NOx removal rate was increased.

Control of DC Corona Discharge Modes by a Switching Operation

AbstractSummary: Glow and streamer discharges are well known as the typical modes for positive DC corona discharges. In this study, a new method for the control of the corona discharges modes is proposed. The grounded electrode is divided and a switch is attached to one of the electrodes. The results showed that corona discharge mode could be controlled by this switching operation. As the applied positive voltage is increased, corona glow is mostly generated in air at atmospheric pressure, but this mode is changed to streamer mode by switching‐off the operation. Moreover, glow and streamer corona discharges from one stressed wire electrode can be generated simultaneously by modifying the design of the divided plane electrodes and by the switching operation. A mechanism of the controlled streamer discharge by the switching operation is discussed.Simultaneous generation of glow and streamer corona discharges from one stressed wire electrode.imageSimultaneous generation of glow and streamer corona discharges from one stressed wire electrode.

Particulate Matter Removal from Diesel Exhaust Gases by a Combination of Corona Discharge and Water or Oil Bath

AbstractSummary: As an efficient PM removal method from diesel exhausts, we developed a new method using a combination of a DC corona discharge and oil or water trays. The PM removal device generates DC corona discharges on oil or water filled in trays, thereby creating charges on the PMs, which can then be accelerated by an electric field towards the oil or water bath. The amount of PM absorbed in oil is determined by measuring light transmission. The discharge current on water is higher than that on oil. The difference of these discharge currents is considered to be due to the difference in ion mobility of the two liquids. An equation for PM removal characteristics is proposed. Using the equation, the PM removal by our device is estimated to be more than 85%.Experimental system for PM removal from diesel engine exhaust gas.imageExperimental system for PM removal from diesel engine exhaust gas.

Comparative studies of dc corona and back discharges in different gases

Direct-current corona discharge and back-discharge generated in needle-plate electrode configuration in air, Ar, N2, or CO2, flowing smoothly through a discharge chamber were investigated. The back discharge is dielectric barrier discharge generated in the presence of normal corona discharge, when the plate electrode is covered with a dielectric layer of high resistivity. In the experiments with back discharge a mica plate was used as the dielectric barrier. A small pinhole was made in the plate center to initiate an electrical breakdown through the dielectric layer. Comparative studies of corona and back-corona discharges at normal temperature and pressure were carried out in the aspects of discharge morphology and the current-voltage characteristics.

Ozone decomposition on walls

In this paper we have estimated the coefficient of ozone decomposition on metallic electrodes (steel, stainless steel and aluminium) in a negative dc corona discharge between a wire and a cylinder in pure oxygen. Using the obtained value of this coefficient and a reduced one-dimensional fluid model, which is described by the continuity and moment transfer equations in the drift diffusion approximation and coupled with the Poisson equation, we have computed the charged and neutral species generated in this discharge.

High voltage breakdown in an inductively coupled ion source

An inductively coupled plasma source, designed for ion beam applications, is allowed to float up to several kilovolt positive. If one side of the radio frequency (rf) antenna is grounded and the dielectric source tube and the surrounding air are allowed to reach a threshold temperature corona breakdown at the rf antenna occurs. The experiments presented here show that a dc corona can be ignited with the presence of a dielectric barrier, which normally precludes dc breakdown. The formation of a negative barrier corona initiates a transition to a continuous arc from the rf antenna to the source tube. It is suggested that the onset of the first filaments heat the dielectric locally, such that the dielectric strength drops. DC current channels are then formed in the source tube, allowing a resistive corona with continuous arcs to exist.

Electron mobility in argon and carbon dioxide

Electron drift velocities were determined in argon and in mixtures of argon with carbon dioxide, using media processed to yield a high degree of purity. The measurements were performed at a pressure of 760 torr and a temperature of 25degC. The medium was confined in a cylindrical measuring chamber made of polytetrafluorethylene (10-mm diameter, 10-mm length). The electrodes used to generate electric field were circular, made of stainless steel, and vacuum coated with gold. A layer of ionized gas (approximately 4 mm thick) was created near the negative electrode with a 10-mCi tritium radioactive source. The cell was connected to a pulse generator with a low duty factor, which ensured that most of the time the medium was in the quiescent state. During the active state, an axial electric field was created in the chamber by a short negative pulse applied to the cathode. To assure purity and to facilitate the transport of calibration samples, the gaseous medium was flown from anode to cathode via the chamber (50 mlmiddotmin-1 ). The layer of plasma near the cathode was electrically neutral most of the time since the electrodes were effectively grounded during the quiescent state. The pulsed electric field separated the charge carriers in the plasma layer into fast electronic and slow ionic charges. The time-amplitude dependence reflected the charge separation dynamics and was used for the determination of drift velocities. The velocity data were measured in ultrahigh-purity argon and in binary mixtures of argon with carbon dioxide (from 1.0%v to 6.5%v). In argon, for field intensities Eisin(0,8) kVmiddotm-1, the velocity range was veisin(0,2.8) kmmiddots-1, and for Eisin(8,35) Vmiddotm-1, veisin(0,2.8) kmmiddots-1. In mixtures of Ar-CO2, electron drift velocity depended on the concentration: For field E=8 kVmiddotm -1, veisin(7,18) kmmiddots-1, and for E=35 kVmiddotm-1, veisin(12,24) kmmiddots-1. The data obtained in this study can be used for the determination of the voltage-current characteristics and other parameters of corona discharges. The data are of interest to those who study the physical phenomena in dc and pulsed corona discharges

DC corona discharge from a wire particle floated with a microgap in parallel plate electrodes

Conductive particles existing in a high-voltage system could deteriorate the system performance owing to an electric discharge via the particles. In case when the particles exist in a dc high-voltage electrode system, the location of the particle would inevitably affect the discharge aspect. A corona-onset and breakdown voltage from a metallic wire particle were measured in detail. The wire particle has a length ranging from 6 to 12 mm, and a diameter of 0.25 mm. It was fixed between a parallel plate electrode with a spacing of 20 or 30 mm. When the particle was close to the negative electrode, a corona discharge occurred stably, and the corona-onset voltage was increased as the gap length between the negative electrode, and the positive end of the particle increased up to 0.8 mm. In contrast, when the particle was close to the positive electrode, the breakdown always occurred without preceding the corona discharge. At the middle region between the electrodes, the corona onset occurred at almost constant voltage

Temporal development and chemical efficiency of positive streamers in a large scale wire-plate reactor as a function of voltage waveform parameters

In this paper a large-scale pulsed corona system is described in which pulse parameters such as pulse rise-time, peak voltage, pulse width and energy per pulse can be varied. The chemical efficiency of the system is determined by measuring ozone production. The temporal and spatial development of the discharge streamers is recorded using an ICCD camera with a shortest exposure time of 5 ns. The camera can be triggered at any moment starting from the time the voltage pulse arrives on the reactor, with an accuracy of less than 1 ns. Measurements were performed on an industrial size wire-plate reactor. The influence of pulse parameters like pulse voltage, DC bias voltage, rise-time and pulse repetition rate on plasma generation was monitored. It was observed that for higher peak voltages, an increase could be seen in the primary streamer velocity, the growth of the primary streamer diameter, the light intensity and the number of streamers per unit length of corona wire. No significant separate influence of DC bias voltage level was observed as long as the total reactor voltage (pulse + DC bias) remained constant and the DC bias voltage remained below the DC corona onset. For those situations in which the plasma appearance changed (e.g. different streamer velocity, diameter, intensity), a change in ozone production was also observed. The best chemical yields were obtained for low voltage (55 kV), low energetic pulses (0.4 J/pulse): 60 g (kWh)−1. For high voltage (86 kV), high energetic pulses (2.3 J/pulse) the yield decreased to approximately 45 g (kWh)−1, still a high value for ozone production in ambient air (RH 42%). The pulse repetition rate has no influence on plasma generation and on chemical efficiency up to 400 pulses per second.

NO x reduction from compression ignition engines with DC corona discharge—An experimental study

An experimental study of DC corona discharge technology for NO x reduction from diesel engine exhaust is presented. The DC corona reactor consists of a flat electrode against a multi-needle electrode. The results are presented in terms of the cleanness (mass of NO x removed relative to its initial mass), and the efficiency (the energy required to theoretically dissociate 1 g of NO x , relative to the energy actually needed). For both cleanness and efficiency, negative polarity (negative needles) is preferable. Cleanness was found to be independent of the engine load. The results show that the performance of a DC corona reactor depends on the reactor length L, electrode separation distance D, and needle density a. The cleanness and efficiency of the NO x decomposition were mapped, and optimal geometrical parameters for the best reactor performance have been obtained. It is concluded that for best performance, the residence time of the exhaust gas inside the reactor should be longer than 1 second ( τ > 1 s ); the electrode separation distance D must be less than 30 mm (for the electric field intensity to remain sufficiently high for dissociation reactions); and the needle separation distance a must not exceed 20 mm (to provide sufficiently dense distribution of plasma regions from each needle). The cleanness and efficiency values for the optimal geometry lay between 55% (cleanness) with 10% (efficiency), and 50% (cleanness) with 18% (efficiency), for needle separation distances a of 10 and 20 mm, respectively.

Finite-element analysis of positive and negative corona discharge in wire-to-plane system

This paper deals with positive and negative corona discharge in atmospheric air using a wire-to-plane system. The Poisson's equation is solved numerically using the finite-element method and the current continuity equation. The space charge density is updated using the simplified method of characteristics, where the ion diffusion is neglected. The numerical model takes into account the avalanche length of the corona discharge and the potential corresponding to the minimum ionisation field is directly introduced in the method on the border of the ionisation region. The end geometry of the linear biased probe without wraparound bias plates has been adapted to a wire-to-plane system for use in DC corona discharge. The current density and the electric field are measured; their spatial distributions are given and compared with the computed values. The agreement between the calculated values and those obtained experimentally is satisfactory. The per unit electric field and current density are also represented by a unique function.

Corona and spark discharges occurring between a grounded sphere and an array of charged multiple electrodes

Corona and spark discharges between a grounded sphere electrode and an array of charged multiple electrodes have been investigated for understanding the characteristics of an electrostatic discharges produced by space charges distributed in three dimension. The electrode array consists of sixty-four 50-cm long by 1-cm diameter conducting rods arranged in an eight-by-eight array with 50-mm spacing between each rod. The entire array was charged by a DC corona discharge. Electrostatic discharges were initiated from the grounded spherical electrode brought in the proximity to the charged array. The electric current and the luminous aspect of the discharge were observed for various sizes of the grounded sphere electrode. The charge distributions of the array before and after the discharge were measured directly. The current waveform and charge transfer of the discharge depend on the polarity of the charged array and the size of the spherical electrode.

The Role of H2O in Nitric Oxide Removal by Wet-Type Corona Discharge Plasma Reactor

We have applied the dc corona discharge process to the removal of NO from a simulated flue gas. The effect of H2O on the oxidation of NO to NO2 was investigated. The experimental results show the removal rate of NO is improved in wet-type reactor than that of dry-type reactor. NO is mostly oxidized into NO2 by the reaction with O and O3 and NO2 is changed into HNO3 by the reaction with OH, which is generated from H2O.

Study of Wastewater Treatment by OH Radicals Using DC and Pulsed Corona Discharge over Water

Water treatment by OH radicals is studied using dc and pulsed corona discharge over water at atmospheric pressure and reduced pressure. In particular, we pay attention to the influence of discharge configuration on the efficiency of wastewater treatment. Experiment is carried out in N2 to clarify the contribution of OH radicals. Needle-cylinder electrodes are designed expecting the efficient generation of OH radicals close to the water surface. N,N-dimethyl- p-nitrosoaniline (RNO) solution is used as a persistent test pollutant. The results strongly suggest that OH radical production close to the water surface is a key factor for efficient wastewater treatment. The use of pulsed discharge at reduced pressure is effective in improving RNO reduction efficiency because of the rapid diffusion of OH radicals to the water surface.

An analysis of the evolution of negative ions produced by a corona ionizer in air

Mass spectrometric measurements of negative ions produced by a dc corona ionizer in air were conducted at different reaction times (ca. 1.0 ms and 10 ms) to observe the evolution of negative ions in air. One of the characteristic features was the rapid dominance of NO 3 − ions in the mass spectra, which is indicative of the strong influence of O 3 and NO 2 produced by discharge in the early stages of negative ion evolution. Water vapor was also found to play a significant role in NO 3 − ion formation. The production of OH radicals by ion–molecule reactions involving H 2O leads to the formation of HNO 3 which accelerates the conversion of primary negative ions to NO 3 − ions. As a result, NO 3 − and NO 3 −HNO 3 ions were observed as terminal ions. Another terminal ion observed was assigned to HCO 3 −HNO 3. The reaction of OH − with CO 2 is probably responsible for the formation of HCO 3 −. From considerations of ion reactivity, NO 3 − ions likely represent the most long-lived ion species in negative ion evolution in indoor air.

Direct Current Corona Field of „Wire-to-Cylinder“ Electrode System

Comparison of the DC corona field in the system „wire-to-cylinder“ with the cylinders radius 2 times greater than the distance between electrodes and in the system „wire-to-plane“ with the same distance between electrodes is performed by using the Deutsch‘s– Popkov‘s method. The space charge of the „wire-to-cylinder“ system increases the field strength on the wire surface by 16 % and decreases it on the surface of cylinder by 69 %. Corresponding quantities of change of the field strength in „wire-to-plane“ system are 8 % and 54 %. Computed value of onset voltage for the system „wire-to-cylinder“ is 4.70 kV, the experimental one – 4.35 kV. Corresponding quantities for „wire-to-plane“ system are 4.55 kV and 4.10kV. Current of discharge for the system „wire-to-plane“ are greater by 25 % in comparison with the values of current for „wire-to-cylinder“ system in the range of voltages near the onset value. This difference is egual to 16 % in the range of voltages exceeding the onset value by 50 %. The DC corona field for the „wire-tocylinder“ system can‘t be changed by the field of the system „wire-to- plane“ for given values of geometric parameters without introducing the substantial errors. It may be done when the radius of cylinder exceed the distance between electrodes more than 10 times. Ill.4, bibl. 6, tabl. 2 (in Lithuanian; summaries in Lithuanian, English and Russian).

Effect of Coexisting Gases on NO Removal Using Corona Discharge

Effects of H2O, CO2, CH4 and C2H4 contained in automotive exhaust gas on NO removal by using a DC corona discharge were investigated experimentally. In this experiment, N2/O2/NO mixture was used as a base gas of the simulated exhaust gas. To clarify the effect of the individual coexisting gas on NO removal, each coexisting gas was added to the base gas. The results showed that the existence of H2O or C2H4 was effective for NO removal with low energy density. Also, when negative corona discharge was applied to the simulated exhaust gas (N2/O2/NO/H2O/CO2/C2H4 mixture), the efficiency of DeNOx was more than 90%. However, the by-products such as CO, O3, HNO3 and N2O increased with increasing the energy density. It was found that the optimum energy density of corona discharge was about 250J/L for DeNOx of simulated exhaust gas.

Sterilisation of Hydroponic Culture Solution Contaminated by Fungi using an Atmospheric Pressure Corona Discharge

The hydroponic culture solution contaminated by fungi is sterilised by a DC corona discharge, and the sterilisation characteristics are investigated in this work. A DC streamer corona discharge is generated at atmospheric pressure in air between needle clusters and a water bath containing contaminated solution by fungus such as Fusarium oxysporum f. sp. spinaciae or Fusarium sp.. It is found that the fungi are killed by the exposure of the corona discharge, and that the death rates of the fungi chiefly depend on the concentration of the hydroponic culture solutions. It is also found that the number densities of the fungi decrease exponentially with the energy expenditure of the corona discharge, and that damping coefficients of the fungi densities depend on the concentration of the hydroponic culture solutions. This suggests that the fungi are chiefly inactivated by electroporation.

Phenol Oxidation in Aqueous Solution by Gas Phase Corona Discharge

AbstractIn this paper, results of phenol degradation in water induced by a DC corona discharge run in air-like gas mixture above the water surface are presented. The DC positive corona discharge was generated between a stressed hollow needle and the water surface. Air with 1.5% CO