CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation

A closed-cycle, three-dimensional (3D) computational fluid dynamics (CFD) analysis campaign was conducted to evaluate the performance of using spark plugs to assist gasoline compression ignition (GCI) combustion during cold idle operations. A conventional spark plug using single-sided J-strap design was put at a location on the cylinder head to facilitate spray-guided spark assistance. Ignition was modeled with an L-type energy distribution to depict the breakdown and the arc-to-glow phases during the energy discharge process. Several key design parameters were investigated, including injector clocking, number of nozzle holes, spray inclusion angle, number of fuel injections, fuel split ratio, and fuel injection timings. The study emphasized the region around the spark gap, focusing on flame kernel formation and development and local equivalence ratio distribution. Flame kernel development and the ignition process were found to correlate strongly with the fuel stratification and the flow velocity near the spark gap. The analysis results showed that the flame kernel development followed the direction of the local flow field. In addition, the local fuel stratification notably influenced early-stage flame kernel development due to varying injection spray patterns and the fuel injection strategies. Among these design parameters, the number of nozzle holes and fuel injection timing had the most significant effects on the engine combustion performance.

Increasing the energy of the initiating spark discharge in order to reduce and stabilize the delay time in a compact vacuum breaker

The similarity of the switching mechanisms of compact vacuum spark breakers and spark breakers with laser ignition is established at a comparable level of energy flux density in the ignition node–ionization of the residual gas by a stream of short-wave radiation and fast electrons from the cathode spot plasma or laser plasma. This mechanism allows you to effectively reduce the delay in triggering the spark gap by increasing the ignition energy. An experimental study of the advantages of using an ignition circuit with increased energy for controlling small-sized vacuum spark breakers is carried out. There is a steady decrease in the delay time of the spark gap and an increase in the level of delay stability. From the point of view of minimization and stability of the delay time of the spark gap, the energy investment in the formation of the initiating plasma occurs most effectively at the spark stage of the auxiliary discharge along the surface of the dielectric in the ignition node.

Design, fabrication, and testing of microelectromechanical system spark gap switch based on streamer theory

In order to realize that the fuze micro system has both high security and miniaturization characteristics, the spark gap research of Micro-Electro-Mechanical System safety system is carried out. So that to solve the safe and reliable function of the spark gap switch under the low power supply voltage (35 V) of the fuze micro system, the gas gap size and electrode radius are shown to significantly affect the gas breakdown voltage using streamer theory. Based on these results, a spark gap switch with triggering electrodes is designed. The triggering electrode gap is 2 μm and the main electrode gap is 10 μm. A spark gap switch test circuit is designed based on the RLC circuit. Through finite element simulation, it is verified that the gas breakdown voltage increases nonlinearly with increasing gap size. Pre-breakdown spark gap switches were fabricated based on the surface silicon process and tested. The test results show that the conduction voltage values of the triggering electrode and the main electrode are basically consistent with the simulation and calculation results. The breakdown voltage of the main electrode can be greatly reduced by applying a certain voltage to the triggering electrode, realize the reliable function in the micro fuze system.

Assessment on the Optimum Performance of a Novel 3 Axes Micro EDM Developed for Commercial Applications

A low cost three axes commercial microEDM machine has been developed indigenously in order to implement precision micromachining. The developed microEDM consists of various components such as machining chamber, X-Y table, tool feed and tool holder assembly, dielectric circulation system, power supply and automatic driving devices to control the spark gap distance. The setup is capable of performing the 8µm movement in Z-axis.The developed 3 axes machine and the commercial available machine are investigated with the most important process parameters such as Current, Pulse on time and Pulse off time in order to study the Material Removal Rate (MRR) and Tool Wear Rate (TWR). The material chosen for the current research is Stainless Steel 316L, which has high corrosion resistance and the electrode was tungsten 300µm. In most of the experiments, the developed machine has performed with 6.52% higher MRR and 26.10% Lower TWR. This is due to the effective spark gap circuit developed with the use of hall current sensor.The mathematical model of MRR and TWR are obtained by correlating the process parameter using Response Surface Methodology (RSM).The chosen objectives are contradictory in nature, we employ a non-dominated Genetic algorithm to find the optimal process parameters. The developed 3 axes microEDM has yield a 10.14% and 33.12% better performance on optimum maximum MRR and minimum TWR respectively when compared to the commercial machine.

Formation of the voltage pulses up to 400 kilovolts with front pulse less than 10 nanoseconds

This work presents basic information about the design, manufacturing technology, and application of small-sized sealed-off spark-gaps in metal-ceramic design with hydrogen filling up to 120 atmospheres at an operating voltage of 100-400 kV with switching energy of up to 10 Joules in pulsed X-ray flaw detectors. The main factors affecting the mechanical strength and stability of the spark-gap operation are described. The results of an experimental study of the switching characteristics of the RO-49 spark gap-sharpeners are presented.

Subnanosecond switching of standard thyristors triggered in impact-ionization wave mode by a high-voltage PCSS driver

Power thyristors triggered in impact-ionization wave mode are capable to replace spark gap switches, bringing major advantages into repetitive pulsed power industrial applications. Low power thyristors remained for the moment out of the research focus, most likely because of the challenging driver, which must provide a sufficiently fast and powerful triggering pulse. This paper describes subnanosecond switching of standard off-the-shelf low-power thyristors in impact-ionization wave mode, running by the PCSS trigger generator based on the laser diode and GaAs switches. Several types of thyristors with a rated voltage from 0.6 kV to 2.2 kV have been tested running by both a commercial FID and by the tailored PCSS generators. The triggering and current flow stages were examined. For the 1.6 kV thyristor (TO-247 package), the following parameters have been obtained: switching time 250 ps, dI/dt up to 12 kA/μs, amplitude 85 A and FWHM about 60 ns. In this mode, the first 103 pulses have not revealed any thyristor degradation.

A Compact High-Power Ultra-Wideband Bipolar Pulse Generator

A compact high-power ultra-wideband bipolar pulse generator based on a modified Marx circuit is designed, which is mainly composed of a primary power supply, Marx generator, sharpening and cutoff subnanosecond spark gap switches, and coaxial transmission lines. The Marx generator with modified circuit structure has thirty-two stages and is composed of eight disk-like modules. Each module consists of four capacitors, two spark gap switches, four charging inductors, and a mechanical support. To simplify the design of the charging structure and reduce the number of switches, four groups of inductors are used to charge the capacitors of the Marx generator, two of which are used for positive voltage charging and the other two for negative voltage charging. When the capacitor of each stage is charged to 35 kV, the maximum output peak voltage can reach 1 MV when the Marx generator is open circuit. The high-voltage pulse generated by the Marx generator charges the transmission line and forms a bipolar pulse through sharpening and cutoff switches. All transmission lines used for bipolar pulse generation have an impedance of 10 Ω. When the 950 kV pulse voltage generated by the Marx generator is fed into the transmission line, the bipolar pulse peak voltage can reach 390 kV, the center frequency of the pulse is about 400 MHz, and the output peak power is about 15.2 GW.

Minimization of the delay time and its spread in a compact vacuum breaker

The similarity of the switching mechanisms of compact vacuum spark breakers and spark breakers with laser ignition is established at a comparable level of energy flux density in the ignition node–ionization of the residual gas by a stream of short-wave radiation and fast electrons from the cathode spot plasma or laser plasma. This mechanism allows you to effectively reduce the delay in triggering the spark gap by increasing the ignition energy. An experimental study of the advantages of using an ignition circuit with increased energy for controlling small-sized vacuum spark breakers is carried out. There is a steady decrease in the delay time of the spark gap and an increase in the level of delay stability. From the point of view of minimization and stability of the delay time of the spark gap, the energy investment in the formation of the initiating plasma occurs most effectively at the spark stage of the auxiliary discharge along the surface of the dielectric in the ignition node.

THERMAL RADIATION IN SPARK DISCHARGE

The work is devoted to numerical study on thermal radiation in spark discharge. The influence of radiative thermal conductivity on the expansion of the spark channel has been established. The study of the effect of value of the capacitance of the discharge capacitor on the energy emitted by the discharge has been carried out. The change in the thermodynamic state of the gas in the spark channel is considered taking into account following factors: change in the capacitance of the discharge capacitor, the length of the discharge gap and the initial gas pressure. The influence of the initial gas pressure and the gap length on the parameters of thermal radiation of a gas under conditions of a constant breakdown voltage supplied to the spark gap is investigated.