Pulsed Spark Discharge Research Articles

Sustainable nitrogen fixation with nanosecond pulsed spark discharges: insights into free-radical-chain reactions

Sustainable plasma-driven N2 oxidation for NOx formation by a nanosecond pulsed spark discharge is proposed to approach the zero-carbon emissions target with new insights into free-radical-chain reactions by kinetics modeling and optical diagnosis.

Experimental investigation of supersonic boundary-layer tripping with a spanwise pulsed spark discharge array

In this paper, a pulsed spark discharge plasma actuator array is deployed to control laminar–turbulent transition in a Mach 3.0 flat-plate boundary layer, and the subtle flow structures are visualized by nanoparticle planar laser scattering (NPLS) technique. Results show that the onset location of turbulence can be brought upstream by plasma actuation, corresponding to forced boundary-layer transition. Hairpin vortex packets evolved from the thermal bulbs play a vital role in the breakdown of laminar flow. With the help of a machine learning tool, all the relevant structures induced by plasma actuation are extracted from NPLS images, and a conceptual model of the hairpin vortex generation is proposed, including three stages: production and lift-up of the high-vorticity region, formation of the $\varLambda$ vortex and evolution of the hairpin vortex.

Optical emission spectroscopy measurement of plasma parameters in a nanosecond pulsed spark discharge for CO2/CH4 dry reforming

In this paper, a nanosecond pulsed spark discharge in CO2/CH4 mixture gas at atmospheric pressure is studied with optical emission spectroscopy. A high-voltage pulse is applied across two plate-shaped electrodes at a repetition frequency of 1 kHz. Emphatically, plasma parameters of this discharge are estimated by spectroscopic methods for giving an insight into the underlying dry reforming reaction mechanism. The time-averaged optical emission is mainly caused by atomic spectral lines of excited O, H, and C+, and C2 swan bands. The vibrational temperature of 8500 ± 50 K and rotational temperature of 3200 ± 100 K are estimated by the excited C2 molecules, respectively. The electron density is calculated by Stark broadening of O (844.6 nm), Hα (656.3 nm), and Hβ (486.1 nm) for 3.4 ∼ 7.71 × 1017 cm−3 while C+ (723.6 nm) for 4.37 × 1018 cm−3 with an electron excitation temperature of 0.58 eV that is estimated by the intensity ratio of Hα and Hβ. The determination of plasma parameters offers essential data for subsequent reaction kinetics research of the plasma-assisted dry reforming of CH4.

Ignition of a Fuel Mixture Using a Multipoint Pulsed Spark Discharge under Various Initial Conditions

Ignition of a Fuel Mixture Using a Multipoint Pulsed Spark Discharge under Various Initial Conditions

Influence of solution electrical conductivity and ionic composition on the performance of a gas–liquid pulsed spark discharge reactor for water treatment

The influence of solution electrical conductivity and ion composition on the performance of plasma reactors for water treatment applications is only partially understood. This study uses a point–point discharge over the surface of water in argon gas to determine the influence of solution conductivity, in the range of 0.3–45 mS/cm, on the physiochemical properties of spark discharges and the removal of two organic contaminants: perfluorooctanoic acid (PFOA) and Rhodamine B dye. The influence of various ions was also explored using chlorine and non-chlorine salts to adjust solution conductivity. The removal of PFOA increased with conductivity regardless of the salt type due to the salting out effect which increased PFOA's interfacial concentration. The removal of Rhodamine B dye depended on both salt type and solution electrical conductivity. In the presence of non-chorine salts, UV photolysis was the main mechanism for the dye degradation and its removal rate did not change with conductivity. The dye removal rate was the highest in the presence of chloride-based salts at the highest values of solution conductivities. In the presence of chorine salts, OH radicals are produced by the discharge generated hypochlorous acid, which is mixed into the bulk solution to react with the Rhodamine B dye. The generation rate of hydroxyl radicals appears to decrease with increasing solution conductivity, and these species are not directly involved in the degradation of the two compounds investigated in this study.

Experimental investigation of incident shock wave/boundary layer interaction controlled by pulsed spark discharge array

The influence of the streamwise-pulsed spark discharge array (S-PSDA) to the incident shock wave/boundary layer interaction (ISWBLI) was investigated via high-speed schlieren imaging system in this paper. Root mean square (RMS) and the fast Fourier transform (FFT) methods were used to analysis the schlieren image sequence. Three frequencies of actuation were applied to ISWBLI. The results indicated that the actuation of 10 kHz could effectively reduce the intensity of the separation shock wave. In contrast, 1 kHz and 5 kHz actuation have little effect to the intensity of the separation shock wave; the turbulence of the boundary was enhanced after the 5 kHz and 10 kHz actuation was applied, in addition, the area of the interaction zone can be reduced in 10 kHz actuation; FFT results indicated that the low-frequency unsteady motion of the separation shock wave will be weakened in 5 kHz actuation and enhanced in 10 kHz actuation.

Experimental investigation on compression ramp shock wave/boundary layer interaction control using plasma actuator array

Particle image velocimetry measurement on shock wave/boundary layer interaction in a Mach 2.0 supersonic wind tunnel is performed to quantitatively reveal the plasma flow control effect in this paper. The typical flow structure is produced by a 24-degree compression ramp model and the streamwise plasma actuator array with five pulsed spark discharge plasma actuators is adopted as the control device. In the midspan plane, the results show that although the separation region exhibits an obvious extension, the foot of the separation wave moves upstream and the shock wave angle decreases from 41.6° to 22.3°, proving the decline in shock intensity. The shock wave drag is estimated to be reduced by 45%. According to the phase-averaged velocity field, the reason that the high-frequency actuation plays a key role in achieving the continuous control effect is revealed through the temporal evolution of the separation region area. Also, another interesting phenomenon that the flow deflects when passing through the actuation region is found, which may induce the upwash and downwash motions of the boundary layer and further reduce the flow separation on both sides of the actuation region. At last, a preliminary conceptual model is proposed to reveal the probable flow control mechanism.

Synthesis of nickel and cobalt oxide nanoparticles by pulsed underwater spark discharges

Electrical discharges in liquids are considered an efficient and ecological technique of nanoparticle synthesis via controlled erosion of electrodes. Herein, we use spark discharges between Co–Co, Ni–Ni, Co–Ni, or Ni–Co electrodes immersed in distilled water to synthesize Co and/or Ni nanoparticles, as well as their oxides. When mixed electrodes are used (Co–Ni or Ni–Co), both Co and Ni nanoparticles are produced, and the major species is dictated by the nature of the anode pin. The characteristics of nanoparticles synthesized under varying conditions of pulse width (100 and 500 ns) and voltage amplitude (5 and 20 kV) are analyzed by transmission electron microscopy. Within the investigated discharge conditions, it is not possible to produce Co–Ni nanoalloys; however, core–shell nanoparticles are observed among the Ni and Co nanoparticles. Finally, the direct optical bandgaps of the nanomaterials are determined using UV-visible absorption spectroscopy.

Gasdynamic Flow Control by Ultrafast Local Heating in a Strongly Nonequilibrium Pulsed Plasma

—The paper presents a review of modern works on gasdynamic flow control using a highly nonequilibrium pulsed plasma. The main attention is paid to the effects based on ultrafast (on the nanosecond time scale for atmospheric pressure) local gas heating, since, at present, the main successes in controlling high-speed flows by means of gas discharges are associated with this thermal mechanism. Attention is paid to the physical mechanisms responsible for the interaction of the discharge with gas flows. The first part of the review outlines the most popular approaches for pulsed energy deposition in plasma aerodynamics: nanosecond surface barrier discharges, pulsed spark discharges, and femto- and nanosecond optical discharges. The mechanisms of ultrafast heating of air at high electric fields realized in these discharges, as well as during the decay of the discharge plasma, are analyzed separately. The second part of the review gives numerous examples of plasma-assisted control of gasdynamic flows. It considers control of the configuration of shock waves in front of a supersonic object, control of its trajectory, control of quasi-stationary separated flows and layers, control of a laminar–turbulent transition, and control of static and dynamic separation of the boundary layer at high angles of attack, as well as issues of the operation of plasma actuators in different weather conditions and the use of plasma for the de-icing of a flying object.

Platinum Based Nanoparticles Produced by a Pulsed Spark Discharge as a Promising Material for Gas Sensors

We have applied spark ablation technology for producing nanoparticles from platinum ingots (purity of 99.97 wt. %) as a feed material by using air as a carrier gas. A maximum production rate of about 400 mg/h was achieved with an energy per pulse of 0.5 J and a pulse repetition rate of 250 Hz. The synthesized nanomaterial, composed of an amorphous platinum oxide PtO (83 wt. %) and a crystalline metallic platinum (17 wt. %), was used for formulating functional colloidal ink. Annealing of the deposited ink at 750 °C resulted in the formation of a polycrystalline material comprising 99.7 wt. % of platinum. To demonstrate the possibility of application of the formulated ink in printed electronics, we have patterned conductive lines and microheaters on alumina substrates and 20 μm thick low-temperature co-fired ceramic (LTCC) membranes with the use of aerosol jet printing technology. The power consumption of microheaters fabricated on LTCC membranes was found to be about 140 mW at a temperature of the hot part of 500 °C, thus allowing one to consider these structures as promising micro-hotplates for metal oxide semiconductor (MOS) gas sensors. The catalytic activity of the synthesized nanoparticles was demonstrated by measuring the resistance transients of the non-sintered microheaters upon exposure to 2500 ppm of hydrogen.

Research on non-contact ultrasonic vibration assisted rotating electrical discharge machining (EDM) machine tool

Electrical discharge machining (EDM) is a nontraditional machining method by using pulsed spark discharge between workpiece and electrode to melt and remove metal. The traditional power supply method uses carbon brush and slip ring. This contact type has power supply at the contact point. Problems such as carbon deposition, leakage, and easy generation of electric sparks restrict the improvement of the rotation speed of the electrode and pose a safety hazard. The non-contact power supply technology based on the principle of electromagnetic induction can effectively solve the above problems, which can provide conditions for high-speed rotation of the electrode. In order to improve the processing quality and efficiency, this study aimed to design a small ultrasonic vibration assisted EDM machine, which can effectively avoid spark concentration and abnormal arc generation.

Воспламенение топливной смеси с помощью многоточечного импульсного искрового разряда при различных начальных условиях

The development of efficient and reliable systems for the ignition of air/fuel mixtures is of interest for many practical applications associated with the use of combustion devices. To increase the total surface of the flame, ensure the reliability of ignition, increase the rate of combustion in the volume of the chamber and the completeness of combustion of the combustible mixture, multi-point ignition of the air/fuel mixture using several pulsed spark discharges is used. A comparison of the characteristics of combustion products in the working chamber when using different numbers of igniting spark discharges is made based on the data of a physical experiment. Measurements are carried out at various ignition points of the mixture, initial mixture pressures, and air/fuel ratios. The values of the air/fuel ratio used in the experiment are in the range, the boundaries of which are the lower and upper concentration limits of the ignition of the propane-air mixture.

Сравнение энергетической эффективности воспламенения топливной смеси искровым и стримерным разрядами

An increase in fuel efficiency and efficiency of combustion processes in power plants is discussed based on the data of physical and computational experiments. Two systems for ignition of a fuel mixture are considered, one of which uses a multi-point pulsed spark discharge, and the other uses a multipoint streamer discharge. A comparative assessment of the energy efficiency of each approach to the ignition of the air/fuel mixture is carried out, and conclusions are drawn about their effectiveness and prospects for use.

Actuation efficiency of nanosecond repetitively pulsed discharges for plasma-assisted swirl flames at pressures up to 3 bar

This study analyzes different strategies of plasma actuation of premixed swirl flames at pressures up to 3 bar. A wide range of applied voltages and pulse repetition frequencies (PRF) is considered, resulting in different combinations of nanosecond repetitively pulsed (NRP) discharge regimes, NRP glow and NRP spark discharges. Electrical characterization of the discharges is performed, measuring voltage and current, and deposited energy and power are evaluated. The effectiveness of the plasma actuation is assessed through images of OH* chemiluminescence from the flame. From these images, the distance of the center of gravity of the flame to the burner plate is evaluated, with and without plasma actuation. The results show that strategies which involve a high percentage of NRP sparks are effective at improving flame anchoring at atmospheric pressure, while they are detrimental at higher pressures. Therefore, high applied voltage and low PRF are preferable at atmospheric pressure, while the opposite is observed at elevated pressures. Moreover, it is found that a ratio of plasma power to thermal power of the flame around 1% is the best compromise between a strong actuation of the flame and a reasonable deposited electrical power. Explanations for these results are proposed.

Compression ramp shock wave/boundary layer interaction control with high-frequency streamwise pulsed spark discharge array

A streamwise array of pulsed spark discharge operating at a high frequency of 10 kHz is used to control the shock wave/boundary layer interaction (SWBLI) induced by a 24° compression ramp (CR) in a Mach 2.0 flow. High-speed schlieren imaging at 50 000 frames/s is deployed for flow visualization. The schlieren snapshots, as well as statistics of the schlieren sequence, show that the intensity weakening effect on the shock wave can be achieved for a long time up to 20 ms, which is the first experimental demonstration of stable control on the CR-SWBLI with plasma actuators. Then, based on fast Fourier transform analyses, the low-frequency unsteadiness of the shock wave is also significantly modified and the dominant oscillation frequency is switched to the high frequency St = 0.32. The mechanism of the encouraging control outcome is finally discussed that the strong separation wave induced by a CR is replaced by a multistage weak compression wave produced through a high-frequency actuator array.

ВЛИЯНИЕ ЭЛЕКТРОГИДРАВЛИЧЕСКОЙ ОБРАБОТКИ НА СОДЕРЖАНИЕ НИТРАТНОГО АЗОТА В ПОЛИВНОЙ ВОДЕ

The introduction of mineral fertilizers has a negative impact on the agrobiocenosis. An increase the concentration of nitrate nitrogen in irrigation water in order to use it as a nitrogen fertilizer that does not have a negative impact on the environment seems relevant. The change in the content of nitrate nitrogen was determined in irrigation water, which was used as the flowing water of the city water supply (Moscow); pond water (Moscow region); potassium nitrate solution with a concentration of 50.9 mg/l. Three types of irrigation water were processed using a high-voltage installation. The experimental electrohydraulic installation consisted of a TVI-50/70 transformer with a rectifier unit; DC electric energy storage systems (high-voltage pulse capacitors); arresters designed to generate pulsed spark discharges with a short rise time; controls that allow changing technological modes during experiments; working units. During the research, an ITAN pH meter/ionometer was used according to the RD 52.24.367-2010 method. The technological mode of operation of the electro-hydraulic unit provides for the following characteristics: operating voltage 42 kV; capacitance of capacitors 0.05 μF; number of spark discharges n = 1 ... 5 thousand pieces; forming the gap between the ball arresters FP = 14 mm; working gap between working high-voltage electrodes 10 mm. Electrohydraulic treatment of water increases the concentration of nitrate nitrogen compounds in the running water of city water supply by 3.7 times (from 2.9 to 10.9 mg/l), in pond water - by 7 times (from 1.2 to 8.4 mg/l), in a solution of potassium nitrate - 1.3 times (from 50.9 to 68.4 mg/l). In water treated electrohydraulically, the content of nitrate nitrogen increases, which expands the possibilities for its use when watering plants.

Anchoring of premixed jet flames in vitiated crossflow with pulsed nanosecond spark discharge

This paper deals with the effect of non-equilibrium plasma on the anchoring of a premixed jet flame in hot vitiated crossflow at atmospheric pressure. The turbulent vitiated crossflow was generated by an array of 4×4 premixed turbulent jet flames burning a lean mixture of air and natural gas at an equivalence ratio of 0.7 and a thermal power of 50 kW. The rich jet, with equivalence ratio ϕjet varied between 1 and 3, was injected perpendicularly to the vitiated crossflow in a rectangular duct, with jet-to-crossflow momentum flux ratios J ranging from 1 to 26. A nanosecond repetitively pulsed discharge was initiated in the vicinity of the windward side of the jet root. The effect of discharge power and repetition rate on the lift-off height of the flame is systematically analyzed for different combinations of ϕjet and J. High speed chemiluminescence imaging of the flame and of the discharge shows that the initiation of the discharge on the windward side of the jet enhances the combustion chemistry, reducing the ignition time and the lift-off height of the flame. It is shown that the nanosecond repetitively pulsed discharges are able to maintain a robust anchoring of the flame for a wide range of operating conditions at relatively low electric power cost. Emission spectroscopy and OH-PLIF measurements were carried out to show that the plasma has both thermal and kinetic effects on flame anchoring respectively via intense localized heating of the mixture at temperatures exceeding 3000 K and via an intense production of OH radicals.

Detection and analysis of spark discharge products of C5F10O by electron attachment mass spectrometry

C5F10O has the potential to replace SF6 as an insulation gas in switchgears due to its high breakdown field strength and low global warming potential. However, as a newly synthesized gas, the chemical characteristics of C5F10O are not well known. In particular, the discharge products of C5F10O are not clear, which limits its insulating capability evaluation in long-term use, and further hinders the development of a gas sensor to monitor the insulation deterioration of C5F10O-containing switchgears. In this paper, electron attachment mass spectrometry (MS) was proposed to detect the decomposed products of C5F10O under pulsed spark discharge condition. It was found that the ionization source of the MS had an optimal electron energy of 2 eV to avoid decomposing the gas molecules to be detected while having a high detection sensitivity. The detected discharge products mainly included CF4, C2F4, C3F6, C3HF5, C3F8, C3HF7, C4F10, C5F10, C6F12, C3F4O and C2F6O, while CF4, C3HF5, C3HF7, C5F10, C6F12, C3F4O and C2F6O were not detected using GCMS. Based on the nonionization measurement, the decomposition mechanism was deduced. Also, it was found that the densities of some products, such as C3F6, C3F8, C4F10 were increasing with the discharge voltage and the number of discharge pulses, implying that these species might be used as indicators for the discharge accumulation effects such as the insulation deterioration of switchgears.

Selective Synthesis of 2D Mesoporous CuO Agglomerates by Pulsed Spark Discharge in Water

Metal oxide nanomaterials, including copper oxide, have attracted great attention due to their unique physical and chemical properties that are dependent on particle size and morphology. In this study, we propose an alternative technique for the synthesis of 2D mesoporous CuO agglomerates that is both efficient and ecological. This technique is based on the use of pulsed spark discharges between copper electrodes immersed in deionized water. Detailed TEM analyses show that the synthesized CuO nanostructures are composed of elementary nanocrystals with sizes in the order of a few nanometers. Assessments of the effects of applied voltage (5 and 20 kV) and discharge pulse width (100 and 500 ns) demonstrate that the latter parameter influences the size and density of nanocrystals in a nanostructure. Moreover, voltage and pulse width may both be used to finely control the direct optical band gap energy of CuO nanostructures between 3.0 and 3.4 eV. The efficient and ecological technique developed in this study produces 2D mesoporous CuO agglomerates that can be readily used in other processes.

Improvement of lean blow out performance of spray and premixed swirled flames using nanosecond repetitively pulsed discharges

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.