Argonne National Laboratory represents the United States’ Department of Energy’s commitment to cooperative research and scientific discovery. Since its inception in 1946, Argonne has pioneered laboratory research and experimentation as the first national laboratory in the United States. While a significant amount of research in the decades following its founding centered around nuclear energy and applications, Argonne has transitioned from nuclear research to include additional energy sources and storage since the beginning of the 21st century. Now, Argonne constitutes a scientific community of leading researchers, with projects across a spectrum of computational, quantum, and interdisciplinary fields.
Among the contributors in this area are Dr. Joohan Kim and Dr. Riccardo Scarcelli. Their work on modeling spark discharge processes in spark-ignition (SI) engines was recently recognized by Argonne. Dr. Kim received a Postdoctoral Performance Award in the area of Engineering Research, along with ten other postdoctoral appointees whose contributions set a standard not only for the quality of their discoveries, but also for the ingenuity of their techniques and demonstrated leadership capabilities. According to Argonne, awardees’ works have upheld core values of scientific impact, integrity, respect, safety, and teamwork.
Within the highly competitive automotive industry, the need for innovation through design presents opportunities for new tools and technologies to be utilized. Regulations from governing entities seek to strike a balance between meeting climate goals through greater restrictions on CO2 emissions from automobiles, while relying on the transportation industry and automotives to fuel trade and commerce. With restrictions focused solely on reducing emissions, applications that meet these criteria without sacrificing capabilities stands out for both manufacturers and legislators alike.
Dr. Kim’s work highlights the need for predictive models which can optimize operational parameters for SI systems in order to maximize thermal efficiency gain and lower engine development costs. Creating these predictive models requires advanced simulation software capable of solving and coupling electromagnetic physics and fluid dynamics into a computational framework. When we asked about his use of simulations, Dr. Kim said, “high-fidelity simulations enable us to perform in-depth analysis of the spark-ignition process, including energy transfer, birth of flame kernel, and thermo-chemical properties; these would be difficult to obtain using experimental techniques only.” He went on to add that, “with a fundamental understanding of complex physics, we can develop predictive models that make simulation-based optimization robust and reliable.”
“VizSpark provided a fully-coupled framework between electromagnetic physics and fluid dynamics, and thereby we were able to diagnose the plasma properties occurring within tens of nanoseconds without many assumptions.”
Dr. Kim’s study utilized VizSpark simulations to accurately estimate electrical discharge shape, as well as temperature and pressure of plasma kernels, thus providing a set of robust initial and boundary conditions for studying flame kernel growth under engine-like conditions. He noted “VizSpark provided a fully-coupled framework between electromagnetic physics and fluid dynamics, and thereby we were able to diagnose the plasma properties occurring within tens of nanoseconds without many assumptions.”
VizSpark is a robust, industrial simulation tool for high-fidelity modeling of thermal (arc) plasmas. Additionally, VizSpark is fully parallelized and can be used to perform large, 3D simulations with complex geometries. Its comprehensive solvers and scalability make it ideal for solving real world engineering problems.
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The future of transportation seems to be increasingly electric. In its latest report on electric vehicles (EV), the International Energy Agency (IEA) highlights a 40% increase in EV demand despite a 16% dip in the global car sales. Moving towards electrified vehicles has also pushed a shift in the vehicle design where the mechanical components are being replaced with electronic-based automotive components. Relays play a critical role in such electrified systems.
A relay is a switch that is operated electrically and is used to control a high power circuit with a low power signal circuit. The most common type of relay is an electromechanical relay that consists of terminals for the signal and the terminals where the supply and load are connected. Upon receiving a signal, an electromagnetically operated armature closes or opens the gap between the supply and the load terminals. Traditional electromechanical relays dominate the market, over solid state relays, because of their advantages in a wide operating range of voltages and currents and the low cost to manufacture due to the simplicity in design. However, the main problem that affects the lifetime of electromechanical relays is arcing.
The primary undesirable effect of arcing is sudden load surge in a circuit. This delays the signal to the primary circuit breaker to isolate the load device, which may fail due to overcurrent. Further, arcing leads to high surface temperature which can erode the terminals and contactors or even weld the contactors to the terminals. Both of these undesirable phenomena cause a great deal of reliability and safety issues. The strength and duration of the arc have a significant impact on the safety of electric vehicles as well as on relay contactor erosion, therefore the lifetime of the relay.
Therefore, it is crucial to study the formation of arcs within relays and explore designs that suppress the arc formation. At Esgee Tech, we delve further into how this disengagement happens and what could be done to improve it further. An insight into these phenomena could allow faster mitigation of arcs and thus quicker response times.
Arc – The Most Energetic Type of Plasma Discharge
A gaseous medium that experiences a sufficiently high electric field results in ionization of the medium which causes the medium to become conductive. We call this an electrical discharge. The characteristics of an electrical discharge depends on the voltage and current as shown in the figure on the left. Discharges carrying large currents, such as illustrated in this blog post, are classified as arcs. Arc is self-sustaining, i.e., it does not require an external ionization source to maintain discharge – the internal electron and gaseous processes maintain structure of the arc.
The physics of arcs is very complex. Ambient pressure, ambient temperature, geometry of the electrodes, gas composition, electromagnetic fields, external circuit parameters and surface properties all dynamically affect the formation and quenching of arcs. Industrial designs of relays need to account for all of these tightly coupled phenomena.
Our engineers at Esgee Tech have developed VizSpark™, a robust and accurate thermalized plasma simulator. VizSpark™ allows coupling of reactive plasma mechanics, fluid dynamics, transient electromagnetics, radiative mechanisms, surface erosion physics, circuit dynamics and continuously morphing boundaries. VizSpark™ also supports complex 3D industrial geometries.
Using VizSpark™ the industrial problem of understanding arcs and optimizing design and safety of EV relays can be effectively addressed at high fidelity.
EV Relay Computational Model and Results:
The electric vehicle relay geometry described in this blog comprises a stationary anode (left terminal), a stationary ground (right terminal) and a movable contactor that disengages to break the circuit. The circuit coupled with this domain is a 220 V DC supply via a load resistor as shown in the figure below. The gas composition in the relay is hydrogen which is kept at a pressure of 1 bar and 300 K. An external magnetic field of 1T is imposed in the z-direction (into the screen).
VizSpark™ captures breakdown of arc between the electrodes accurately as shown in the illustration below. Initially, about 35A flows through the arc, upon ignition. The Arc stretches outwards due to Lorentz force generated by the interaction of the arc with the external magnetic field. The total resistance of the arc increases as it stretches. This decreases the current and cools down the arc as temperature decreases due to reduction in joule heating. The partially extinguished arc reignites several times, around 400 µs, before finally extinguishing, in a phenomenon called restrike. VizSpark™ accurately simulates the stretching of the arc and formation of a new filament during restrikes. This is seen as a “saw-tooth” waveform in both transient voltage and current graphs.
As the gap between the contactor and terminals increases, the conditions are unfavorable for restrikes and fewer restrikes are seen in the later stages of the simulation. The potential across the gap increases to 220V and the current drops to 0A which marks a completely extinguished arc and the relay circuit is open.
Trade Studies with VizSpark™
A variety of methods can be applied to ensure faster quenching of the arc, which reduces the electrical cutoff time. A few techniques to extinguish the arc quickly are: stretching the arc through external magnetic fields, increasing the speed of the moving contactor, using gas mixtures that absorb electrons such as SF6, using gas mixtures with high thermal conductivities such as hydrogen, and using an arc chute/splitter plates to divide the main arc into smaller faster dissipating arcs. Further, use of external circuits such as snubber circuits which consist of a series configuration capacitor and resistor connected in parallel across the relay suppresses the spike in current as the voltage starts to fluctuate during arc quenching. All of these configurations can be simulated at fidelity using VizSpark™.
The computational model shown here is capable of incorporating comprehensive arc physics necessary to study quenching behavior in high-voltage EV relays. The model can be used to perform design/parametric studies on EV relays in reasonable computational time. Future work should involve detailed validation of the model with existing experimental data. Other avenues of research include incorporating eroded metal vapor, the inclusion of arc chute or splitter plates, and electrode deformation due to erosion.
We hope you are someone who is as fascinated about plasma flow simulations as we are, feel free to follow us at LinkedIn or reach out to us at email@example.com.
In the meantime, explore the following journal articles (do ask us for a free copy!):
Karpatne, A., Breden, D., and Raja, L., “Simulation of Arc Quenching in Hermetically Sealed Electric Vehicle Relays,” SAE Int. J. Passeng. Cars – Electron. Electr. Syst. 11(3):149-157, 2018, https://doi.org/10.4271/2018-01-0765.
N. Ben Jemaa, L. Doublet, L. Morin and D. Jeannot, “Break arc study for the new electrical level of 42 V in automotive applications,” Proceedings of the Forth-Seventh IEEE Holm Conference on Electrical Contacts (IEEE Cat. No.01CH37192), 2001, pp. 50-55, https://www.doi.org/10.1109/HOLM.2001.953189
Esgee Technologies is excited to attend the International Conference on Ignition Systems for Gasoline Engines next week, December 6-7, in Berlin, Germany.
Join Esgee Tech’s Doug Breden for his talk on “Numerical Modelling of Electrode Ablation for Spark Plug Lifetime Prediction.” He’ll discuss how high-fidelity arc simulation, combined with dynamic surface deformation and timescale acceleration techniques, can be used to effectively predict spark plug life. This capability reduces the need for field testing, expands design space exploration, and enables the potential for lifetime optimization in spark plug designs.
The maximum lifetime of a spark plug is limited by electrode erosion. Over the course of millions of repeated sparking events, the electrode material ablates and the electrode gap increases which degrades performance. Once a critical gap is reached, the spark plug is no longer operational and must be replaced. Due to the long relevant time scales over which erosion occurs, and the difficulty of analyzing the spark plug environment during operation, determining spark plug lifetime typically requires extensive field testing.
The objective of this work is use a computational model that can accurately simulate the electrode erosion process and make predictions on the effective lifetime. The problem is challenging in that there are a vast range of time scales, all of which must be resolved to model the erosion. Time scales range from milliseconds needed to resolve arc physics up to days and weeks for time timescales of electrode deformation due to ablation.
As a first step, dynamic coupling between arc physics and an ablating, eroding electrode is developed. An existing commercial arc solver code-VizSpark, capable of modelling the spark event with high fidelity, is used to model the arc physics which determine the net heat fluxes to the electrodes. The electrodes are modelled using an immersed object method, which allows them to dynamically change in shape as the simulation progresses. Mass flux from the electrodes due to ablation is modelled using temperature dependent metal vapor pressure curves. As mass is removed from the electrode-gas interface, the immersed object dynamically deforms, which in turn modifies the gap voltage and the arc physics. Overall, this approach provides predictive capability for the arc-induced erosion over the entire life-time of the spark-plug.
High-voltage relays perform a key role in determining safety and protections of Electric Vehicles(EV)/ hybrid automotive systems. The primary function of a high voltage relay is to mechanically separate electrodes under a short circuit situation, and isolate the motor drive electronics from impending damage due to high currents (~1000 A). As the relay breaks contact, significant arcing can occur due to high currents. Several methods can be applied to ensure immediate mitigation of arc within the relay, thereby reducing the electrical cutoff time. One such technique is to draw the arc towards the walls of a hermetically sealed chamber (using external magnets), and quenching it as it makes contact with the wall. Other techniques involve using an inert gas within the chamber to prevent arcing to occur in the first place.
This paper discusses the numerical modeling of arc formation and mitigation inside sealed electric vehicle relay. A high-fidelity, multi-dimensional, equilibrium arc solver-VizSpark is used to model the dynamics of arc formation and mitigation. Electrode motion is modeled using an immersed object method. The effect of several parameters such as pressure, gas composition and magnetic field strength on arc propagation speeds and cut-off time are studied.