Characteristics Of Spark Discharges Research Articles

Experimental study on electrostatic spark discharge under different electrode parameters, pressure and gas component

In this work, the influence of different experimental parameters (electrode gap, electrode shape, pressure and gas component) on spark discharge characteristics is investigated. The dynamic processes of voltage, current, energy, and power during the spark discharge process are analyzed. Electrical characteristic parameters including the discharge energy, discharge efficiency, spark resistance and total resistance are studied. High-speed schlieren technology is used to visualize the spark discharge and shock wave formation under different pressure and electrode shapes. The effect of pressure on the shape, radius and average velocity of the shock wave is investigated.

In vitro degradation and corrosion evaluations of plasma electrolytic oxidized Mg–Zn–Ca–Si alloys for biomedical applications

Biodegradable calcium phosphate (CaP) ceramic coatings were prepared on self-designed Mg-2.0Zn-0.6Ca-xSi alloys by plasma electrolytic oxidation (PEO). The effect of calcium (Ca) and silicon (Si) on alloy microstructure and coating formation and biomineralization mechanisms were discussed. The in vitro bioactivity and degradability of CaP coatings were evaluated by immersion tests in simulated body fluid (SBF) solutions and trishydroxymethyl-aminomethane hydrochloric acid (Tris-HCl) buffer, respectively. The microstructure and chemical composition of the coatings, depositions and corrosion products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and fourier transform infrared spectrometer (FT-IR). The electrochemical corrosion behavior of alloys and coatings was investigated using the electrochemical workstation. Results showed that the shape, quantity, size and distribution of second phases can be changed by the simultaneously addition of Ca and Si in Mg–Zn–Ca–Si alloys. The Si content in Mg-2.0Zn-0.6Ca-xSi alloy should not be higher than 0.8 wt%. The microstructure of Mg-2.0Zn-0.6Ca-xSi alloys can influence the formation and growth of PEO coating by altering the spark discharge characteristics. The plasma electrolytic oxidized Mg-2.0Zn-0.6Ca-0.8Si has potential to be served as biodegradable bone implant and cardiovascular stent.

Experimental investigation the effects of spark discharge characteristics on the heavy-duty spark ignition natural gas engine at low load condition

The fuel economy of natural gas (NG) spark ignition (SI) engine could improve significantly when using high exhaust gas recirculation (EGR) dilution. However, the combustion processes become instability and even occur misfire at higher EGR rate. In this paper, the high energy ignition system, which was the technology of variable spark, was utilized to extend the EGR tolerance of a SI engine. Extensive experimental tests were conducted to investigate the effects of spark discharge current and duration on combustion and emissions characteristics at low load condition. The results showed that the fuel economy was improved with the spark discharge energy at the high EGR rate of 30%. The increase amplitude of fuel economy was 1.32% when the spark discharge energy increased from 210 to 320 mJ. The effective spark discharge energy was existed in consideration of the fuel economy. The ignition delay (CA0-5) and the flame propagation period (CA10-90) shortened with an increase in spark discharge energy. Besides, NOx emissions were more sensitive to the spark discharge energy than that of HC and CO emissions. As the spark discharge energy increased, the increase extent of NOx emissions was 26.9%, while HC and CO emissions decrease slightly.

Cylindrical Air-Gap Electrode Spark Discharge Characterization and Quenching

Spark discharges were parametrically examined for a cylindrical air-gap electrode configuration. The aim of this study was to elucidate spark discharge characteristics, arc penetration, and exhaust plume development to guide designers of relevant ignition devices. Spark gaps ranged from 0.5 to 2.3 mm, nominal pressures ranged from 150 to 2200 kPa, and two exciter types (bipolar and unipolar) were tested. Positive correlations were observed between the pressure–distance product and multiple dependent variables: breakdown voltage, energy discharged, and percentage of sparks quenched. Positive correlations were observed between the pressure–distance quotient and various other dependent variables: spark duration, channel resistance, and plume velocity. This study also discusses the effects of quenching on electrical measurements, how these effects are nontrivial, and the subtle irregularities in electrical results that are indicative of quenching.

Data-driven analysis of relight variability of jet fuels induced by turbulence

For safety purposes, reliable reignition of aircraft engines in the event of flame blow-out is a critical requirement. Typically, an external ignition source in the form of a spark is used to achieve a stable flame in the combustor. However, such forced turbulent ignition may not always successfully relight the combustor, mainly because the state of the combustor cannot be precisely determined. Uncertainty in the turbulent flow inside the combustor, inflow conditions, and spark discharge characteristics can lead to variability in sparking outcomes even for nominally identical operating conditions. Prior studies have shown that of all the uncertain parameters, turbulence is often dominant and can drastically alter ignition behavior. For instance, even when different fuels have similar ignition delay times, their ignition behavior in practical systems can be completely different. In practical operating conditions, it is challenging to understand why ignition fails and how much variation in outcomes can be expected. The focus of this work is to understand relight variability induced by turbulence for two different aircraft fuels, namely Jet-A and a variant named C1. A detailed, previously developed simulation approach is used to generate a large number of successful and failed ignition events. Using this data, the cause of misfire is evaluated based on a discriminant analysis that delineates the difference between turbulent initial conditions that lead to ignition or failure. From the discriminant analysis, a compressed sensing algorithm is then applied to help pinpoint the locations of relevant turbulent features. Findings from the discriminant analysis are confirmed with the time history of near kernel properties. Next, a clustering strategy is used to identify ignition and misfire modes. With this approach, it was determined that the cause of ignition failure is different for the two fuels. While it was found that Jet-A is influenced by fuel entrainment, C1 was found to be more sensitive to small scale turbulence features. A larger variability is found in the ignition modes of C1, which can be subject to extreme events induced by kernel breakdown.

Evaluation of spark discharge

Electric sparks can ignite fires, initiate explosions, shock humans. These discharges release energies through very complex dynamic processes. The effects of changing energy (capacitance and voltage) and electrode parameters on spark discharge characteristics are investigated. A multi-energy high-voltage ignition system is built. Results show that the spark discharge energy by voltage is more stable than changing the energy by capacitance. The breakdown characteristics of electrodes are revealed under different electrode parameters by the field strength distribution of the electrode. The energy utilization efficiency of large electrode gap is about 5.55% higher than that of small electrode gap.

Effect of deep cryogenic treatment on the microstructure and corrosion behavior of the microarc oxidized Mg-2.0Zn-0.5Ca alloy

Biodegradable microarc oxidation (MAO) coatings were prepared on the Mg-2.0Zn-0.5Ca alloys treated with and without deep cryogenic treatment (DCT). Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to characterize the coating morphology and phase composition. The electrochemical corrosion behavior was investigated using the electrochemical workstation. The effects of DCT on the formation mechanism and corrosion behavior of the MAO coatings were investigated. The results indicate that the DCT has refining effect on the Mg-2.0Zn-0.5Ca alloy. The mechanisms of the coating formation and growth can be influenced by the introduction of the DCT through influencing the grain size, phase precipitation and crystal defect states of the substrate. The changing of the microstructure of the alloy can alter the spark discharge characteristics of the MAO reaction. The DCT has an effect on the controllability of the corrosion rate of the MAO coated samples.

Influence of spark discharge characteristics on ignition and combustion process and the lean operation limit in a spark ignition engine

Lean combustion technologies have been investigated to decrease the heat loss of spark ignition engines. However, as the excess air ratio approaches the lean operation limit, the cycle-to-cycle variation of combustion becomes an obstacle to improving thermal efficiency. This paper discusses the influences of spark discharge characteristics, such as discharge current and spark-shortening phenomena, on the ignition and combustion process under lean conditions (excess air ratio (λ) of 1.8–2.3) to suppress the cycle-to-cycle variation of combustion and extend the lean operation limit. In this study, a customized inductive ignition system equipped with 20 conventional ignition coils was applied to enhance the ignition energy. The discharge interval between each coil unit was controlled to change the discharge current and duration. The results show that the in-cylinder discharged energy increased with the discharge interval. The cycle-to-cycle variation of combustion was minimized when the discharge interval was 0.4 ms, and consequently, the lean operation limit was extended to an excess air ratio (λ) of 2.1. The discharge waveforms indicated that the longer discharge interval could promote spark-shortening phenomena such as re-strike due to the lower discharge current. Finally, in-cylinder photographs of ignition and combustion process showed that the flame kernel formation could be promoted by the repetition of spark-shortening phenomena such as re-strike, as well as by the high elongation of the spark channel.

Time lag characteristics of spark discharge in humid air with increased voltage

This study investigates experimentally the time lag (τ) characteristics of lightning impulse spark discharges in air with relative humidity (RH) over the range 20 to 80%. The experiment was conducted using a wire-plate electrode system with a 30 mm gap and with overvoltage of 30 to 50% of the DC sparking voltage. The statistical and formative time lags (τs and τf) are discussed relative to the effects of RH and overvoltage on electron attachment and detachment mechanisims.

Study on volt-ampere characteristics of spark discharge for transistor resistor pulse power of EDM

Electrical discharge machining (EDM) is widely used in aerospace industry and difficult-to-machine materials field. But the research on machining mechanism is insufficient and it has become a bottleneck of restricting its further development. In this paper, spark discharge self-sustaining conditions, the effects of pulse power circuit parameters on gap volt-ampere characteristics of EDM, formation of maintaining voltage of spark discharge, frequency and amplitude fluctuation of high-frequency components of maintaining voltage, and stability of spark discharge state are studied. Forming process of maintaining voltage of spark discharge is analyzed through discharge main circuit structure of transistor resistor pulse power. Influence of current-limiting resistor on maintaining voltage of spark discharge is also studied. The effect law of current-limiting resistor on oscillation frequency of maintaining voltage of spark discharge is obtained through spectrum analysis of maintaining voltage of spark discharge by methods of fast Fourier transform (FFT). Gap spark discharge control system is established through discharge circuit model of transistor resistor pulse power and the gap of EDM is replaced by spark discharge gap equivalent form. Input of the control system is the voltage of pulse power and its output is the gap voltage. Influence of current-limiting resistor on stability and response speed of the system is analyzed. The above research is important for revealing the mechanism of EDM, maintaining the stability of spark discharge, and guiding the design of pulse power and selection of processing parameters.

Characteristics of Spark Discharge from Faulty Insulators

SUMMARYThe radiation field from the spark discharge on faulty insulators of distribution lines often influences broadcasting services of radio and television, and communication services. The spark discharge occurs due to loose connection in a metal‐fittings connection of strain insulators. The rust of metal‐fittings and the low‐tension of wire are causes of loose connection. In this paper, the generation conditions of spark discharge were clarified by the basic experiment. And the radiation field which includes frequency component of several GHz due to the spark discharge was measured using a 6.6 kV full‐scale distribution line, and the amplitude probability distribution of electric field was analyzed.

Comparison of the electrical characteristics of spark discharges in a layer of metal and graphite granules immersed in liquid

Distinctions and general regularities of the electric characteristics of discharges have been experimentally studied using a model of spatial electrospark dispersion for different parameters of an electric circuit, with the replacement of water by a hydrocarbon medium, the presence or absence of synthesized powder materials in it, and the application of graphite granules in the place of metal ones. The results are presented in this work.

Visualization and concentration measurement of a direct-injection hydrogen jet in a constant-volume vessel using spark-induced breakdown spectroscopy

In this work, spark-induced breakdown spectroscopy (SIBS) was employed to investigate the mixing process of a hydrogen jet in a constant-volume vessel. The local fuel concentration of the hydrogen jet was measured at several locations, using a SIBS sensor. A high-speed camera was used to visualize spark discharge fluctuations, and hydrogen jet concentration measurements were conducted simultaneously. Spectrally resolved atomic emissions from the plasma generated by the spark plug were examined to determine the local equivalence ratio. Direct visualization of the spark discharge provided useful information about the influence of spark discharge characteristics related to the spark timing. Using the developed SIBS sensor, atomic emission spectra were obtained from hydrogen Hα at 656 nm and nitrogen N (I) at 501 nm. Comparison of the intensity peaks of atomic emissions from hydrogen and nitrogen allows the local hydrogen concentration in a measured volume to be determined, and hence also the local equivalence ratio. The measurement results demonstrate the local variation in the equivalence ratio throughout the jet and along its axis. From the results, the spatial structure of the hydrogen jet affects the hydrogen/nitrogen mixing and could be clarified with SIBS technique when the spark is discharged.

Оptical characteristics of spark discharge with composite and metal electrodes

Досліджено випромінювання плазми на основі іскрового розряду з мідними та композиційними електродами (сполука СuInSe 2 ). Виникнення іскрового розряду спричинено дією високовольтного наносекундного імпульсу напруги на відповідні електроди. Отримані емісійні характеристики плазми іскрового розряду при різних міжелектродних відстанях (0,5 мм мідні та 3 мм композиційні електроди). Вста ­ нов ­ лено , що випромінювання плазми іскрового розряду визначалося спектраль ­ ними лініями елементів, що входять до складу відповідних електродів.

Effects of improving current characteristics of spark discharge on underwater shock waves

We have been developing a food-processing device that uses underwater shock waves generated by spark discharges at an underwater spark gap. Underwater shock waves can be used in food processing for softening, fracturing and sterilization. These technologies are attracting attention because the food is not heated during processing, so it does not change flavour. In this study, we develop a rice-powder manufacturing system using the fracturing effect provided by underwater shock waves. Because rice grains are very hard, the process must be applied repeatedly using a momentary high pressure to fracture the grains. The fast repeated generation of shock waves should provide high pressures from low energies. Therefore, we aim to achieve higher pressures from low energies expended by the underwater gap discharge. We increase the pulse compression rate by decreasing the circuit impedance of the device and increasing the charging voltage. Using optical observations and a pressure sensor, we measure the high pressure developed by the underwater shock wave and the rise time of the discharge current. We find that we can decrease the rise time of the discharge current by 17% while maintaining the peak current, and simultaneously increase the high pressure of the underwater shock wave by 135%.

Output short-circuit spark discharging energy and output intrinsic safety criterion of Buck converters

To obtain the output intrinsic safety criterion of Buck converters, the experimental research on its output-short circuit discharge characteristics is conducted by using the safety spark test apparatus. It is found that its spark discharge process can be divided into four stages, i.e., the dielectric-breakdown, spark-generation, spark-keeping and spark-extinguishment. According to the obtained spark discharge characteristics, the output short-circuit spark discharging energy (OSSDE) is deeply analyzed. It is indicated that the OSSDE of the Buck converter with a given inductance is a concave function of load resistance RL when RL is less than the critical resistance RLC corresponding to this inductance, while that is a convex function of RL in the case of RL > RLC. Considering the actual parameter range of the Buck converter, it is further pointed out that when RL RLC, the OSSDE increases with the increase of RL and reaches its maximum in the case of RL=RLC; when RL > RLC, the OSSDE first increases and then decreases with the increase of RL and reaches its maximum in the case of RL, DCM. The most dangerous operating conditions of the converter in whole dynamic range are obtained, i.e., the converter operates in DCM when the input voltage is the highest and RL=RL, DCM. Meanwhile, the maximum OSSDE is achieved. According to the energy equivalence, an output intrinsic safety criterion for Buck converter is proposed by modeling the output short-circuit discharging behaviour as a simple capacitive circuit. The theoretical analysis and proposed criterion are verified by the simulation and experimental results.

Measurement of minimum ignition energies of dust clouds in the

The lower energy limit of current standard test apparatus for determining the minimum ignition energy (MIE) of dust clouds is in the range of 1–3 mJ. This is a quite severe limitation because many dusts ignite readily at this energy level. A new spark generator, capable of producing synchronised sparks of very low energies and with an integrated system for measurement of spark energy, has therefore been developed and employed to a number of easily ignitable dusts. Before testing the MIE of dust clouds, it was considered essential to calibrate the new spark generator against a gas of known MIE. For this purpose, a mixture of propane and air was selected. However, a comprehensive literature review revealed that the reported MIEs of this gas mixture vary significantly, depending on the spark discharge characteristics, including discharge duration. When taking these factors into account, it was concluded that the new spark generator yielded reasonable results for propane/air. Applying the new spark generator to explosive dust clouds showed that a number of dusts do in fact have MIEs that are one to two orders of magnitude lower than 1 mJ. The new spark generator may therefore offer a basis for developing a standard test apparatus in the low-energy region. When using a method of triggering the spark by the explosive dust cloud itself, which probably is a more industrially relevant process than synchronisation between the dust dispersion and sparkover, somewhat higher MIEs were found compared to those determined when using synchronised sparks. However, even with this method of spark triggering, MIEs below 1 mJ were found.

Studies of the parameters of a spark discharge between an artificial charged water-aerosol cloud and the ground

The optical and current characteristics of spark discharges between a grounded electrode and a strongly charged artificial water-aerosol cloud are studied experimentally. The spectral characteristics of the discharge current are investigated using wavelet and Fourier analyses. Three main types of discharge with different final stages are revealed and investigated. It is found that the parameters of a discharge in its final stage depend substantially on the discharge trajectory and the depth to which it penetrates into the aerosol cloud. It is shown that the parameters of the most powerful type of discharge (the brightness of the discharge channel, the current growth rate in the final stage, and the penetration depth into the charged aerosol cloud) are close to the discharge parameters in the main stage of natural lightning. It is also shown that such a discharge neutralizes up to 5% of the cloud charge. In contrast to Fourier analysis, wavelet analysis shows that the signal amplitude (i.e., the energy deposition rate in the discharge channel) is maximum at high frequencies for all types of discharge. Of special interest is the most powerful type of discharge, in which the signal amplitude (which is one to two orders of magnitude larger than in other discharges) is maximum at frequencies of several hundred megahertz.

Effect of potassium fluoride in electrolytic solution on the structure and properties of microarc oxidation coatings on magnesium alloy

Oxide coatings were produced on AM60B magnesium alloy substrate making use of microarc oxidation (MAO) technique. The effect of KF addition in the Na 2SiO 3–KOH electrolytic solution on the microarc oxidation process and the structure, composition, and properties of the oxide coatings was investigated. It was found that the addition of KF into the Na 2SiO 3–KOH electrolytic solution caused increase in the electrolyte conductivity and decrease in the work voltage and final voltage in the MAO process. Subsequently, the pore diameter and surface roughness of the microarc oxidation coating were decreased by the addition of KF, while the coating compactness was increased. At the same time, the phase compositions of the coatings also varied after the addition of KF in the electrolytic solution, owing to the participation of KF in the reaction and its incorporation into the oxide coating. Moreover, the coating formed in the electrolytic solution with KF had a higher surface hardness and better wear-resistance than that formed in the solution without KF, which was attributed to the changes in the spark discharge characteristics and the compositions and structures of the oxide coatings after the addition of KF.

Multiple-Spark Discharge Occurring Between a Charged Conductive Plate and a Grounded Sphere Electrode

The characteristics of spark discharges occurring between a conductive square plate charged by induction charging and a grounded sphere electrode have been investigated experimentally for various plate sizes and charging voltages. The spark discharge having double or multiple peaks in the current waveform occurred from a positively charged plate with particular size and charging voltage. The double-spark discharge was reproducible. The peak values of both the first and the second peak significantly depended on the plate size and charging voltage. From the observations of the luminous aspects and the induction current due to the discharge event, it was found that the double-spark discharge would be caused by the incomplete first spark with relatively less conductive spark channel.