Gas Spark Research Articles

Study on flame-vortex interaction in a spark ignition engine fueled with methane/carbon dioxide gases

A numerical study on the in-cylinder flame-vortex interaction of gaseous spark ignited engine fueled with methane/carbon dioxide is carried out by means of large-eddy method. Evolution of in-cylinder turbulence in charge phase and flame-vortex interaction during combustion process is analyzed in great detail. It's found out that the large scale coherent structures are transformed into homogeneous small scale vortexes during the intake and compression stroke. The strong vortex cores are generated by interaction between flame and in-cylinder background turbulence. Those generated vortex cores wrinkle flame surface and augment turbulent flame speed. The contra-rotation between the two vortexes of vortex-pair in the unburned area results in the appearance of large scale flame wrinkles, which is because the vortex-pair movement leads to the local entrainment and hence stretchs of the flame surface. With the increase of volume fraction of carbon dioxide in the gases, the turbulent flame speed is decreased, the effect of vortex pair on the flame structure is weakened, and the level of the flame wrinkling is decreased correspondingly.

Space-time evolution of ejected plasma for the triggering of gas switch

Ejected plasma has been widely applied to the discharge process of gas spark switches as a trigger technology, and the development process of ejected plasma has a direct and important effect on the discharge characteristics of gas switches. In this paper, both the injection characteristics and space-time evolution of ejected plasma for the triggering of gas spark switch with different stored energies, pulse polarities, and pressures are studied. The discharge characteristics and breakdown process of a gas switch ignited by ejected plasma under different working coefficients are also discussed briefly. The results show that stored energy has significant influence on the characteristics of ejected plasma. With the increase of stored energy, the propulsion mode of ejected plasma in the axial direction transforms from “plasmoid” to “plasma flow,” and the distribution of the ejected plasma goes through “cloud,” “core-cloud,” and “branch” in sequence. The velocity of ejected plasma under negative pulse polarity is obviously higher than that under positive pulse polarity, especially at the very beginning time. The radial dimensions of ejected plasma under two kinds of pulse polarities follow the similar varying pattern over time, which increase first and then decrease, assuming an inverted “U”-shaped curve. With the increase of pressure, the velocity of ejected plasma significantly decreases and the “branch” channels droop earlier. Applying the ejected plasma to the triggering of a gas switch, the switch can be triggered reliably in a much wide working coefficient range of 10%–90%. With the increase of working coefficient, the breakdown process of the switch translates from slow working mode to fast working mode, and the delay time reduces from tens of μs to hundreds of ns.

Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.

Electrode Erosion Characteristics of Repetitive Long-Life Gas Spark Switch Under Airtight Conditions

With the rapid developments in pulse power technology, the gas spark switch has broadened its application in both industrial fields and research fields, such as the extraction of unconventional gas resources and underwater electrical wire explosion. Thus, the repetitive switch needs high current capability, small breakdown voltage variance, and long lifetime in an airtight cavity. The performances of the switch directly influence the output characteristics of the system, but electrode erosion is inevitable, which may decrease the self-breakdown voltage and the lifetime. The purpose of this paper was to investigate the electrode erosion characteristics under adverse conditions. The cathode showed a worse erosion surface. Compared with the central zone of the electrodes, the outer zone showed a worse surface roughness for both the cathode and the anode.

Study on Graphite-Electrode Gas Switch Applied for Pulsed Power Supply With a 700-kA Peak Current

A 700-kA gas switch with graphite electrodes for pulsed power supply module has been developed. This paper describes the design, construction, and testing of the high-current gas switch and its trigger system. The two-electrode gas switch is selected, which suffers high peak and fast rise time currents. The trigger generator based on resonant charging of a pulse transformer is constructed to trigger the gas spark. An electrodynamic force model of switch electrodes is established. The electrodynamic force of connecting wires is also calculated. By comparison of the mechanical strengths of polyformaldehyde, epoxy, and fiber-reinforced plastic (FRP) rods, where FRP rods are selected as switch rods, the experimental results show that the mechanical strength of the switch increases by 200%. Extensive electric testing has proven the operating parameters of the switch and its trigger system. The experimental results show that the measured discharge current waveform is demonstrated to be over a 700-kA peak current and a 500- $\mu \text{s}$ pulsewidth. The transfer charge per shot is more than 500 C.

Injection characteristics of gaseous jet injected by a single-hole nozzle direct injector

Engine manufacturers have focused on natural gas spark ignition engines due to the strict regulations for the reduction of emission levels. However, the characteristics of injectors play an important role in mixture formation and combustion. Two methods to identify the injection characteristics of the gaseous fuel injector which is applied in Spark Ignition Direct Injection (SIDI) engine are described. The first method studies the structure of Compressed Natural Gas (CNG) jet which is directly injected into an optical constant volume chamber for different pressure ratios. Schlieren photography is used to visualize the jet development. The correlation of tip penetration for near and far field of the jet is presented. The second experiment investigates the variations of mass flow rate due to variation of injection pressure and pressure of chamber. The results of this method indicate that mass flow rate through the injector is affected by the injection pressure linearly while it is not influenced by the pressure of chamber.

Ejection of Electrode Molten Droplet and Its Effect on the Degradation of Insulator in Gas Spark Switches

Electrode erosion is a notable issue influencing the performance and restricting the lifetime of gas switches. In the erosion process, electrode materials heated by spark channel will melt or evaporate and be driven to depart from electrode surface, contaminating the gas switch insulator, and potentially inducing flashover accidents. In this paper, sputtering spots are observed near the erosion crater in a two-electrode gas switch, which indicates the existence of molten droplet ejection. In addition, a set of polymethyl methacrylate rings are inserted in the gas switch to detect the ejection of molten droplet as well as to simulate the switch insulator for investigating the degradation of surface insulation strength. The results show that the ejection of molten droplet is along the tangent surface of electrode with a small divergent angle. After repeated discharges, the insulator surface is bombarded by the droplet ejection and forms dense cracks and embedded metal particles in a narrow band. The spatial varied droplet ejection causes a decrease in both flashover electric field and surface resistance. It also leads to different surface resistances in different regions, which can result in an uneven electric field distribution. Thus, droplet ejection increases the probability of surface flashover accidents in gas switches.

Optically isolated, 2 kHz repetition rate, 4 kV solid-state pulse trigger generator.

This paper presents the design and operation characteristics of a solid-state high voltage pulse generator. Its primary utilization is aimed at triggering a gaseous spark gap with high repeatability. Specifically, the trigger generator is designed to achieve a risetime on the order of 0.1 kV/ns to trigger the first stage, trigatron spark gap of a 10-stage, 500 kV Marx generator. The major design components are comprised of a 60 W constant current DC-DC converter for high voltage charging, a single 4 kV thyristor, a step-up pulse transformer, and magnetic switch for pulse steepening. A risetime of <30 ns and pulse magnitude of 4 kV is achieved matching the simulated performance of the design.

Machining characteristics of hard and brittle insulating materials with mist-jetting electrochemical discharge

A new electrochemical discharge machining (EDM) method that combines slotted metal wheel and mist-jetting electrolyte was proposed based on existing problems in the traditional electrolytic EDM compound machining of hard and brittle insulating materials. The physical process of this new method can be divided into four stages, namely the gas film generation, discharge channel formation, material removal, and deionization. We analyzed the inter-polar voltage and current characteristic during machining and found the suitable machining voltage and range of rotation speed for the slotted metal wheel to achieve stable electrochemical discharge machining. The voltage should be more than 220 V, and the rotation speed of the slotted metal wheel should range from 1200 to 1800 rpm during machining. By analyzing the waveform of the voltage and current during mist-jetting electrochemical machining, we found that the machining status included direct gas spark discharge and electrochemical gas spark discharge and that the electrochemical gas spark discharge was primary. Finally, we realized the stable machining of Al2O3 ceramic by using the proposed method. The efficiency of material removal was 53.5 mg/min, and the surface roughness of the machining surface was Ra 5.4 μm.

Characterization of cycle-to-cycle variations in a natural gas spark ignition engine

In this work a study of the influence of the fuel/air equivalence ratio and engine rotational speed on the cycle-to-cycle variations in combustion in a natural gas spark ignition engine is presented. The study considers both classic estimators of cyclic dispersion and a new one, based on the burned mass and burning rate. The engine experimental conditions were as follows: Intake pressure 0.5bar, while fuel/air equivalence ratio was changed from 1.0 to 0.63, and engine rotational speed was varied from 1000rpm to 2500rpm. For each equivalence ratio and engine speed, a diagnosis model is used to process the experimentally obtained combustion pressure data in order to provide combustion relevant results such as the mass burning rate at a cycle level. A procedure based on the use of genetic algorithms is used to obtain a very accurate and objective (without human intervention) adjustment of the optimum parameters needed for combustion diagnosis: angular positioning and pressure offset of the pressure register, dynamic compression ratio, and heat transfer coefficients. The model allows making the diagnosis of series of 830 consecutive engine cycles in an automatic way, increasing the objectivity of the combustion diagnosis. The paper focuses on using the values of the mass fraction burned computed from the pressure register and especially on the analysis of the combustion cycle to cycle variation in the natural gas fuelled engine. A new indicator for the study of cycle-to-cycle variations is proposed, i.e. the standard deviation of the mass fraction burning rate. The values of this new indicator are compared with other classic indicators, showing the same general trends. However, a deeper insight is provided on the combustion cyclic variation when the values of the new indicator are plotted as a function of the mass fraction burned, since this allows analyzing the cyclic variation along the combustion development in each cycle from a mass fraction burned of zero to one, with a relevant value at mass fraction burned of 0.5. More important is that the consideration of the dependence of the combustion variables (density, flame front surface, combustion speed) on the mass fraction burned allows ensemble averaging of all registered cycles for each value of mass fraction burned. This permits using the ensemble averaged mass fraction burning rate as an estimator of combustion speed.The analysis of the general trends of cyclic dispersion when engine speed and equivalence ratio are modified (1000, 1750 and 2500rpm; 0.7, 0.8, 0.9 and 1.0) indicate that cycle-to-cycle variations show, as expected, a strong dependence on the engine rotational speed, increasing the variation with engine rpm. However, when the standard deviation of mass fraction burning rate is plotted as a function of mass fraction burned, there is a linear dependence on engine rpm, but only a very weak dependence on equivalence ratio. This means that the proposed estimator of cyclic dispersion is sensitive to only flow turbulent intensity and not to equivalence ratio.

Experimental and economic study of a gasification plant fuelled with olive industry wastes

Spain is the first olive oil maker worldwide. Yearly, the olive oil industry generates large amounts of by-products: olive pomace, tree pruning, pits, leaves and branches. This work presents the experimental and feasibility study of a pilot plant for the conversion of olive tree pruning and olive pits into electrical and thermal power. The pilot plant is composed of a downdraft gasifier, gas cooling-cleaning stage and spark ignition engine with a modified carburetor. The experimental results showed satisfactory cold gas efficiency (in the range of 70.7–75.5%) and good lower calorific value of the producer gas for both raw materials (4.8 and 5.4MJkg−1). Moreover, the plant achieved acceptable values for the electric and CHP efficiency: 15% and almost 50%, respectively. Finally, the investment achieved reasonable profitability index with a payback period of 5–6years. As a result, the energy recovery potential from the olive industry wastes may represent a good opportunity to promote distributed generation systems.

Experimental investigations of argon spark gap recovery times by developing a high voltage double pulse generator.

The voltage recovery in a spark gap for repetitive switching has been a long research interest. A two-pulse technique is used to determine the voltage recovery times of gas spark gap switch with argon gas. First pulse is applied to the spark gap to over-volt the gap and initiate the breakdown and second pulse is used to determine the recovery voltage of the gap. A pulse transformer based double pulse generator capable of generating 40 kV peak pulses with rise time of 300 ns and 1.5 μs FWHM and with a delay of 10 μs-1 s was developed. A matrix transformer topology is used to get fast rise times by reducing L(l)C(d) product in the circuit. Recovery Experiments have been conducted for 2 mm, 3 mm, and 4 mm gap length with 0-2 bars pressure for argon gas. Electrodes of a sparkgap chamber are of rogowsky profile type, made up of stainless steel material, and thickness of 15 mm are used in the recovery study. The variation in the distance and pressure effects the recovery rate of the spark gap. An intermediate plateu is observed in the spark gap recovery curves. Recovery time decreases with increase in pressure and shorter gaps in length are recovering faster than longer gaps.

Breakdown characteristics of gas spark switch for fast linear transformer driver under DC and pulse combined voltage

The breakdown delay processes of gas switches under combined voltages of DC and pulse voltages in the faster linear transformer driver (FLTD) are analyzed. A formula is presented to estimate the delay time. The three-electrode gas switches used in the present FLTD were preliminarily tested under combined voltages to investigate the breakdown characteristics by experiment. The experimental results indicate that, as applying the combined voltage of 70 kV DC voltage and 300 kV/30 ns fast pulse voltage, the delay time of switches under the combined voltages is smaller than that of normal trigger method. When gas switches are insulated by SF6, the delay time decreases by 17%-30%. While the delay time decreases by 50% with N2 as the dielectric. At the working coefficient of 55%, the jitter is less than 5 ns. Moreover, the estimated delay time is in close agreement with the experimental result.

Thermodynamic analysis and comparison of downdraft gasifiers integrated with gas turbine, spark and compression ignition engines for distributed power generation

The objective of the present article is to assess and compare the performance of electricity generation systems integrated with downdraft biomass gasifiers for distributed power generation. A model for estimating the electric power generation of internal combustion engines and gas turbines powered by syngas was developed. First, the model determines the syngas composition and the lower heating value; and second, these data are used to evaluate power generation in Otto, Diesel, and Brayton cycles. Four synthesis gas compositions were tested for gasification with: air; pure oxygen; 60% oxygen with 40% steam; and 60% air with 40% steam. The results show a maximum power ratio of 0.567 kWh/Nm3 for the gas turbine system, 0.647 kWh/Nm3 for the compression ignition engine, and 0.775 kWh/Nm3 for the spark-ignition engine while running on synthesis gas which was produced using pure oxygen as gasification agent. When these three systems run on synthesis gas produced using atmospheric air as gasification agent, the maximum power ratios were 0.274 kWh/Nm3 for the gas turbine system, 0.302 kWh/Nm3 for CIE, and 0.282 kWh/Nm3 for SIE. The relationship between power output and synthesis gas flow variations is presented as is the dependence of efficiency on compression ratios. Since the maximum attainable power ratio of CIE is higher than that of SIE for gasification with air, more research should be performed on utilization of synthesis gas in CIE.

LTD模块气体开关电极材料烧蚀性能实验

LTD模块气体开关电极材料烧蚀性能实验

气体开关前沿陡化的实验研究

气体开关前沿陡化的实验研究

气体火花开关电极烧蚀研究

气体火花开关电极烧蚀研究

直流叠加脉冲电压下FLTD气体开关击穿特性

直流叠加脉冲电压下FLTD气体开关击穿特性

气体火花开关重复频率特性的实验研究

气体火花开关重复频率特性的实验研究

Performance of an Otto cycle engine using biogas as fuel

Due to the rising price of petroleum, researches looking for alternative fuels are intensifying more and more. Brazil has a great availability of biogas from anaerobic digestion of waste in rural areas, of urban waste in landfills and of sewage treatment systems on urban centers. In this paper, an Otto cycle engine was evaluated on a dynamometer, fed with biogas, generating the characteristic curves of the engine for torque and power. First were made control tests, using the systems commercially available for these fuels, so they could serve as a comparative for the other tests. Next were made tests for the several combinations of ignition point, gas mixer and compression rate. By the analysis of the results, it can be concluded that the best power result for biogas was obtained when used compression rate 12.5:1, long gas mixer and spark advance 45°, because in these conditions, it was obtained the maximum power, superior to original biogas. Key words: Energy, biomass, stationary engine, generator.