•X-ray CT indicates variations of 20% in the L/D ratio and 4% in the nozzle area relative to design dimensions.•X-ray radiography reveals plume density variations of up to 17% about the mean.•The ...plumes exit the holes at up to 5 degrees smaller than the hole drill angle.•The plumes converge with increasing distance from the nozzle.•The plumes also converge with time, which may promote spray collapse.
Gasoline direct injection (GDI) sprays are complex multiphase flows. When compared to multi-hole diesel sprays, the plumes are closely spaced, and the sprays are more likely to interact. The effects of multi-jet interaction on entrainment and spray targeting can be influenced by small variations in the mass fluxes from the holes, which in turn depend on transients in the needle movement and small-scale details of the internal geometry. In this paper, we present a comprehensive overview of a multi-institutional effort to experimentally characterize the internal geometry and near-nozzle flow of the Engine Combustion Network (ECN) Spray G gasoline injector. In order to develop a complete picture of the near-nozzle flow, a standardized setup was shared between facilities. A wide range of techniques were employed, including both X-ray and visible-light diagnostics. The novel aspects of this work include both new experimental measurements, and a comparison of the results across different techniques and facilities. The breadth and depth of the data reveal phenomena which were not apparent from analysis of the individual data sets. We show that plume-to-plume variations in the mass fluxes from the holes can cause large-scale asymmetries in the entrainment field and spray structure. Both internal flow transients and small-scale geometric features can have an effect on the external flow. The sharp turning angle of the flow into the holes also causes an inward vectoring of the plumes relative to the hole drill angle, which increases with time due to entrainment of gas into a low-pressure region between the plumes. These factors increase the likelihood of spray collapse with longer injection durations.
•In our previous work, an ensemble of Convolutional Neural Network (CNN) models was used to predict engine-out emissions of Carbon Monoxide (CO), Unburned Hydrocarbons (HC) and Smoke directly from ...in-cylinder contours of multiple scalar fields.•In this short communication, several modifications were made to the image data generation and training procedure.•The generalization capability of the re-trained deep learning model was investigated by evaluating its prediction performance on a test dataset that was not used previously for training, validation or testing.
In our previous work 1, an ensemble of Convolutional Neural Network (CNN) models was used to predict engine-out emissions of Carbon Monoxide (CO), Unburned Hydrocarbons (HC) and Smoke directly from in-cylinder contours of multiple scalar fields - Equivalence Ratio, Temperature, Velocity and Turbulent Kinetic Energy (TKE) at Exhaust Valve Opening (EVO) generated by physics based Computational Fluid Dynamics (CFD) simulations and experimentally measured emissions data. A dataset of 600 CFD generated images, one for each engine operating condition, from a 1.6L light-duty diesel engine was used for training, validation and testing of the CNN ensemble model. In this short communication, several modifications were made to the image data generation and training procedure. The ensemble of CNN models was re-trained per the new procedure on the modified image dataset from the 1.6L engine. The generalization capability of this re-trained deep learning model was investigated by evaluating its prediction performance on a test dataset from a 3.0L diesel engine that was not used previously for training, validation or testing. The CNN ensemble model re-trained on the 1.6L engine dataset captured the qualitative trends for all three emissions species on the 3.0L engine test dataset, however, quantitatively its prediction performance was not as good. Future work with additional engines and input features is planned to improve the generalization performance of the CNN based emissions prediction model.
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In the case of fusion devices with long pulses or continuous operation, conventional magnetic sensors, such as inductive sensors, have to be supplemented by steady-state magnetic field sensors. ...Therefore, the Hall sensors are considered as a part of the DEMO magnetic diagnostics. The paper reviews the present status of the DEMO steady-state magnetic field sensors based on the ceramics-metal Hall sensors with a sensing layer made of antimony. The mission of the Hall sensors and their operating requirements are summarized, and the design of the Hall sensor assembly is presented. Satisfactory results of initial tests of the sensors are described.
This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in ...operation at UKAEA Culham, UK in 1992-2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006-2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.
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•The remote operation of the tokamak GOLEM for educational purposes.
Practically oriented education in the field of thermonuclear fusion is highly requested. However, the high ...complexity of appropriate experiments makes it difficult to develop and maintain laboratories where students can take part in hands-on experiments in this field of study. One possible solution is to establish centres with specific high temperature plasma experiments where students can visit such a laboratory and perform their experiments in-situ. With the advancements of IT technologies it naturally follows to make a step forward and connect these with necessary plasma physics technologies and thus allow to access even sophisticated experiments remotely. Tokamak GOLEM is a small, modest device with its infrastructure linked to web technologies allowing students to set-up necessary discharge parameters, submit them into a queue and within minutes obtain the results in the form of a discharge homepage.
Abstract
In future fusion reactors disruptions must be avoided at all costs. Disruptions due to the density limit (DL) are typically described by the power-independent Greenwald scaling. Recently, a ...power dependence of the disruptive DL was predicted by several authors (Zanca
et al
2019
Nucl. Fusion
59
126011; Giacomin
et al
2022
Phys. Rev. Lett.
128
185003; Singh and Diamond 2022
Plasma Phys. Control. Fusion
64
084004; Stroth
et al
2022
Nucl. Fusion
62
076008; Brown and Goldston 2021
Nucl. Mater. Energy
27
101002). It is investigated whether this increases the operational range of the tokamak. Increasing the heating power in the L-mode can induce an L-H transition, and therefore a power-dependent DL and the L-H transition cannot be considered independently. The different models are tested on a data base for separatrix parameters at the separatrix of ASDEX Upgrade and compared with the concept (SepOS) presented in Eich and Manz (2021
Nucl. Fusion
61
086017). The disruptive separatrix density scales with the power
n
e
∝
P
0.38
±
0.08
in good agreement to all models. Also the back transition from high to low (H-L) confinement shows an approximately Greenwald scaling with an additional power dependence
n
e
∝
P
0.4
according to the SepOS concept. For future devices operating at much higher heating power such a power scaling may allow operation at much higher separatrix densities than are common in H-mode operation. Preconditions to extrapolation for future devices are discussed.
•A CFD study of multiphase GDI internal flow and near-field spray is described.•Excellent agreement to experimental ROI is achieved with transient needle motion.•Qualitative agreement to experimental ...imaging in the near-field is shown.•Complex internal nozzle flow is shown to influence ROI and spray angle.•Unsteady vortices cause string flash-boiling and expansion of the near-field spray.
A computational study was performed to investigate the influence of transient needle motion on gasoline direct injection (GDI) internal nozzle flow and near-field sprays. Simulations were conducted with a compressible Eulerian flow solver modeling liquid, vapor, and non-condensable gas phases with a diffuse interface. Variable rate generation and condensation of fuel vapor were captured using the homogeneous relaxation model (HRM). The non-flashing (spray G) and flashing (spray G2) conditions specified by the Engine Combustion Network were modeled using the nominal spray G nozzle geometry. Transient needle lift and wobble were based upon ensemble averaged X-ray imaging preformed at Argonne National Lab. The minimum needle lift simulated was 5 µm and dynamic mesh motion was achieved with Laplacian smoothing. The results were qualitatively validated against experimental imaging and the experimental rate of injection profile was captured accurately using pressure boundary conditions and needle motion to actuate the injection. Low needle lift is shown to result in vapor generation near the injector seat. Finally, the internal injector flow is shown to be highly complex, containing many transient and interacting vortices which result in perturbations in the spray angle and fluctuations in the mass flux. This complex internal flow also results in intermittent string flash-boiling when a strong vortex is injected and the resulting swirling spray contains a thermal non-equilibrium vapor core.
The GOLEM tokamak was operated remotely via Internet connection during the 6th International Workshop and Summer School on Plasma Physics. Performances of hydrogen and helium discharges are compared ...in this paper. It is found, at similar vacuum conditions, that helium discharges are shorter but the breakdown of the working gas can be quite easily achieved at almost the same loop voltage. The plasma current in helium discharges is slightly lower than in the case of hydrogen. Turbulent fluctuations of the floating potential measured by means of an array of Langmuir probes reveal a noticeably different character in the two discharges.
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