Operating Regimes Research Articles

ANALYSIS OF ALTERNATIVE FUEL PROCESSING TECHNOLOGIES

The article presents the results of a comparative analysis and experimental testing of the efficiency of technological processes for the processing of some types of alternative energy sources into fuel for transport engines.
 The accumulated research experience in the development of on-board conversion systems (reactors) of traditional motor fuels shows that the level of their technical and technological complexity is incomparable with the ecological and economic effect of their use in an RTS power plant. The high temperature level of the processing of these fuels necessitates the need for additional energy expenditure for the organization of the conversion process (for example, burning part of the fuel to support the necessary thermal regime of operation in thermochemical reactors), and the presence of sulfur compounds in motor fuel excludes the possibility of using highly efficient catalysts. In addition, the large relative content of inert (non-combustible) components in the composition of the target conversion products create additional difficulties when they are burned in the engine. In general, the choice of an acceptable alternative energy carrier as a raw product for the production of motor fuel is a compromise that takes into account its energy value, temperature conditions of conversion, the spectrum of gases formed during conversion, cost, availability of raw materials, the possibility of adaptation to the conditions of the RTS, etc. From the set of factors considered above, it can be concluded that today methanol is one of the most energetically beneficial sources of cheap and efficient hydrogen-containing fuel for RTS engines. It should be noted that in the future, in the world of technology development and the corresponding raw material bases, it may be economically justified to use other compounds, which, according to their characteristics, will be able to meet the energetically favorable conditions in the technological structure of the on-board conversion implementation. This will allow creating a stable fuel and energy base , which practically does not depend on the imported hydrocarbon fuel.

Power-dependent effective reflection of fiber Bragg grating as output coupler of Ytterbium-doped fiber laser

In this paper, we discuss the effective reflection of a fiber Bragg grating and its dependence on laser power when it is used as an output coupler of an ytterbium-doped fiber laser (here the effective reflection is considered to be a part of intracavity laser power reflected by the grating back to the laser cavity). We propose and discuss an experimental technique based on spectral and power analysis and derive simple formulae that permits one to obtain the intra-cavity power and the grating effective reflection. We show that, due to spectral broadening, the effective reflection dramatically decreases with increasing laser power, the effect precisely fitted using the derived formulae describing this quantity. The experimental part of the present study is based on an analysis of the operational regime of a long-wavelength ytterbium-doped fiber laser.

On Flame Extinction and Free-Floating Limits Using a Large Diameter Opposed Jet Burner

ABSTRACT This paper presents studies on flame extinction and associated flame structure using a large diameter (40 mm) opposed jet burner for the first time. The extinction experiments were carried out at various nozzle separation distance (L) to diameter (D) ratios (L/Ds) for methane-air non-premixed flames, while all similar experiments in the past literature are with smaller burner diameters (<25 mm). The extinction studies were used to determine the free-floating limits of the burner, and a detailed analysis of the effect of nozzle exit diameter and Applied Stress Rates (ASRs) on the free-floating limits are reported by comparing with similar works in the past. The Particle Image Velocimetry (PIV) technique was used to determine the axial velocity profiles and local extinction strain rates (Kl) of the flames. Based on the experiments, a correlation for the free-floating separation distance from the stagnation plane (zFF) is proposed, which was found to be proportional to the square of the ASRs. The reported free-floating limits in the literature using various diameters agree with the observed data trend. This solves the ambiguity regarding the free-floating limits of opposed jet burners and provides a general trend of the free-floating separation distance (LFF) even in the off-extinction operation regime. 2D axisymmetric simulations were carried out using realistic boundary conditions on the OpenFOAM® platform to predict flame extinction and, consequently, global flame extinction strain rates (Kg). The model predicts the Kg values and also its trend with L/Ds accurately. The model also captures the flame structure before extinction for various L/Ds.

Водопотребление галеги восточной (galega orientalis lam.) при орошении на дерново-подзолистой почве в северо-восточной части Республики Беларусь.

The article presents the results of the study of water consumption of Galega orientalis on sodpodzolic soils in the north-eastern part of the Republic of Belarus. Based on the obtained field data, the total water consumption was calculated not only for each of the options, but also for different growing seasons. Bioclimatic coefficients have been obtained for calculating the water consumption of Galeag orientalis, which can further be used in calculating the water regime and the need for irrigation of this crop both in the design and in the operational regime of irrigation.

Shannon Entropy Analysis of Reservoir-Triggered Seismicity at Song Tranh 2 Hydropower Plant, Vietnam

The reservoir-triggered seismicity at the Song Tranh 2 reservoir in Vietnam is investigated by using Shannon entropy, a well-known informational method used to analyze complexity in time series in terms of disorder and uncertainty. The application of the time-varying Shannon entropy to the time series of the interevent times of seismicity has evidenced clear links with the temporal fluctuations of the water level of the reservoir, strengthening the belief that the reservoir operational regime is one of the sources of the seismicity occurring in the area. Shannon entropy has also shed light on the tectonic mechanisms of generation of reservoir-triggered seismicity, revealing that the change in stress due to the variation in water level causes the seismic system to be in a state of greater disorder and instability, well depicted by Shannon entropy, which would lead to an increase in seismic activity.

Conversion of combined heat and power coal-fired plants to Carnot batteries - Prospective sites for early grid-scale applications

Repurposing fossil fuel-fired plants to electricity storage systems known as Carnot batteries (CB) has been proposed before. This technology provides a prospect of high-power, high-capacity systems for medium and long duration storage. Significant benefits on capital cost from second use of the existing infrastructure and low cost per added MWh are expected to outweigh low round-trip efficiency. Retrofitting large coal plants is still demanding in terms of absolute capital, lack of previous experience and uncertain business. This work proposes smaller coal-fired combined heat and power plants with 50 MWe output as a suitable prospective site for conversion to CB instead of large power plants. Higher overall efficiency with heat providing an additional stream of revenue, plant flexibility, or smaller system size make such application more beneficial, especially for first-of-a-kind installations.Therefore, this paper illustratively investigates the techno-economic prospects of the conversion of a cogeneration coal plant to a CB. The proposed system is described. It is based on direct electrical heating for the power to heat process, thermal energy storage based on either molten salts or gravel packed bed and finally, heat exchangers integrated to operate as steam generators. The sizing of major components is followed by costing. In case of a backpressure turbine, packed bed storage and discharge duration of 5 h the specific cost of electrical storage system is around 200 €/kWhe, while in the case with no heat production and condensing turbine (full condensation regime), it is around 100 €/kWhe. The operation regimes and expected revenue streams from both electricity and heat are evaluated. A comparison with existing technologies is performed and the levelised cost of storage in presented cases varies from 35 to 179 €/MWhe for the fully condensing regime and 35 to 291 €/MWhe for the backpressure cogeneration regime.

Nonlinear actuation of micromechanical Casimir oscillators with topological insulator materials toward chaotic motion: Sensitivity on magnetization and dielectric properties.

We have investigated the dynamical actuation of micro-electromechanical systems under the influence of attractive and repulsive Casimir forces between topological insulator plates as a function of their dielectric function and coating magnetization. The analysis of the Casimir force in the limit of strong and weak magnetization shows that the attractive force, which is produced for plate magnetizations in the same direction, is greater than the repulsive force that is produced for opposite magnetizations. However, both forces remain comparable for intermediate magnetizations. Moreover, for weak magnetization, the attractive force becomes stronger for an increasing dielectric function, while the opposite occurs for the repulsive force. On the other hand, increasing magnetization decreases the influence of the dielectric function on both the repulsive and attractive forces. Furthermore, for conservative systems, bifurcation and phase portrait analysis revealed that increasing magnetization decreases the regime of stable operation for devices with attractive forces, while their operation remains always stable under the presence of repulsive forces. Finally, for non-conservative periodically driven systems, the Melnikov function and Poincaré portrait analysis show that for magnetizations in the same direction leading to strong attractive Casimir forces, chaotic motion toward stiction is highly likely to occur preventing the long-term prediction of actuating dynamics. A remedy for this situation is obtained by the application of any magnetization in opposite directions between the interacting surfaces since the repulsive force makes it possible to prevent stiction.

Enabling the Internet of Bodies Through Capacitive Body Channel Access Schemes

The Internet of Bodies (IoB) is an imminent extension of the vast Internet of Things (IoT) domain, where wearable, ingestible, injectable, and implantable smart objects form a network in, on, and around the human body. The highly radiative nature of radio-frequency (RF) IoB devices unnecessarily extends the coverage range beyond the human body, which reduces energy efficiency, causes co-existence and interference issues, and exposes sensitive personal data to security threats. Alternatively, capacitive body channel communication (BCC) confine signal transmission to the human body to reduce signal leakage, experience less propagation loss, and reach pJ/b energy efficiency levels. Therefore, capacitive BCC is a key enabler to reach the ultimate design goals of ultra low power, high throughput, and small form-factor IoB devices. Albeit these attractive features, the communication and networking aspects of the capacitive BCC are not thoroughly explored yet. Therefore, this article proposes orthogonal and nonorthogonal capacitive body channel access schemes with or without cooperation among the IoB nodes. In order to address the Quality of Service (QoS) demand scenarios of different IoB applications, we present and formulate the max–min rate, max-sum rate, and QoS sufficient operational regimes, and then provide closed-form and numerical solution optimal power and phase time allocations. Extensive numerical results are analyzed to compare the performance of orthogonal and nonorthogonal schemes with and without cooperation for various design parameters under prescribed QoS regimes. The obtained results show that capacitive body channel access schemes can provide several Mb/s rates even at low transmission powers ranging between −60 and −90 dBm. Moreover, the cooperative schemes are shown to be effective to avoid performance degradation caused by increasing network size, low transmission power, and poor channel quality.

Experimental Study of Nano-Structural Coatings Formed by Microwave Plasma

A novel microwave plasma (MP) torch on a rectangular waveguide with two magnetron sources 2.45 GHz and an experimental setup are designed to perform hydroxyapatite (HA) coatings on metallic and dielectric substrates. Operating regimes of a such torch are investigated. Experimental studies have proved the advantages of this method of HA coating in comparison with analogous techniques. The proposed design is suitable for application in other technologies of different materials processing. Results obtained in the present study help to better understand the processes of nano-structural layer formation on solid substrates.

Predictive modeling of operation scenarios with negative central magnetic shear and large-radius ITBs on EAST

Negative central magnetic shear or magnetic shear reversal is an attractive aspect for advanced operation scenarios in tokamaks as it suppresses turbulence and facilitates the formation of internal transport barriers (ITBs). The advanced operation scenario with negative magnetic shear, which is associated with high confinement quality, a large bootstrap fraction, ITBs, and so on, is one of the future goals of the experiments on EAST. In this work, modeling efforts have been made to find the operation regimes on EAST with negative central shear and large-radius ITBs. The modeling results indicate that negative central shear and large-radius ITBs can be achieved when the electron density is 〈ne〉/nG &amp;gt; 0.7 and the off-axis deposited electron cyclotron heating (ECH) power is 2 MW. Additionally, scenarios with lower ECH power (∼1.5 MW) have been studied since at present, the maximum ECH power that can be provided on EAST is 1.5 MW. With a lower off-axis ECH power of 1.5 MW, scenarios with negative central shear and large-radius ITBs but with a higher electron density of 〈ne〉/nG &amp;gt; 0.8 are obtained. The same as the first case, if the electron density is reduced to 〈ne〉/nG = 0.8 in this case, large-radius ITBs disappeared in the predicted scenario. This reveals that high electron density and large off-axis deposited ECH power are important for scenarios that have q-profiles with negative central shear and large-radius ITBs since lower hybrid current drive (LHCD) tends to peak near the axis at lower electron density, and hence, it helps to increase the temperature gradient near the axis, which will promote bootstrap in this region, leading to a centrally peaked total current density profile. Higher off-axis deposited ECH power helps to obtain scenarios with strong negative central shear and large-radius ITBs at a lower density. Scenarios predicted in this work will guide future experiments on EAST.

Assessments of hydropower plants start-up sequences and equivalent runner damage under transient operation

With specific reference to the HPP start-up sequence, the conventional process requires to operate the runner in a particular operating regime called Speed-No-Load (SNL) that is detrimental for the runner. Thanks to last decade’s improvements in MW-class power electronics, new generators’ technologies have emerged providing an additional degree of freedom to HPPs control. In this respect, the control of the hydraulic turbine speed can be used to decrease the level of damage induced on the runner by choosing the appropriate trajectory for transient operations. Variable speed is a recent technology and its capability to improve the transient operation of hydraulic machines is not fully addressed in literature and, specifically, for start-up sequences. To fully take advantage of such an added degree of freedom, an in-depth experimental study has been performed at EPFL (PTMH) on a specific speed homologous reduced scale model of the unit 5 of Z’Mutt HPP equipped with a reversible pump-turbine. The paper presents a methodology to (i) investigate different transient sequences to start-up the hydraulic machine, which have been tested on reduced scale model, and to (ii) evaluate the equivalent damage impact on the runner. The results of this study highlight the advantages of leveraging the variable speed technology during the unit start-up.

Impact of runner crown shape modifications on the onset of the precessing vortex core

In this experimental study, a passive flow control concept is provided to extend the stable part load operation regime by shifting the rise of the precessing vortex core (PVC), also known as vortex rope, toward lower mass flows respectively deeper part loads. A parametrized runner crown design working as a passive flow control device is derived. This control device aims for shifting the bifurcation point of the PVC to lower flow rates. To determine the most influential design parameters and derive an optimized runner crown design, a design of experiments (DoE) approach is used. This DoE approach is based on data obtained from differential pressure sensors inside the draft tube wall of a generic hydro turbine test rig using air as working fluid. By means of stochastic modeling, the growth rate of the PVC mode is derived from the statistics of the measured pressure signals. The growth rate is used to estimate the bifurcation point of the PVC characterized by a certain normalized flow rate. It is shown that the stable part load operation regime is extended by up to 25% due to the passive impact of the modified runner crown. Moreover, the operational range featuring considerable PVC-induced pressure oscillations is diminished and the pressure recovery of the draft tube is improved compared to the baseline case.

Computations of the shear stresses distribution experienced by passive particles as they circulate in turbulent flow: A case study for vWF protein molecules.

The stress distribution along the trajectories of passive particles released in turbulent flow were computed with the use of Lagrangian methods and direct numerical simulations. The flow fields selected were transitional Poiseuille-Couette flow situations found in ventricular assist devices and turbulent flows at conditions found in blood pumps. The passive particle properties were selected to represent molecules of the von Willebrand factor (vWF) protein. Damage to the vWF molecule can cause disease, most often related to hemostasis. The hydrodynamic shear stresses along the trajectories of the particles were calculated and the changes in the distribution of stresses were determined for proteins released in different locations in the flow field and as a function of exposure time. The stress distributions indicated that even when the average applied stress was within a safe operating regime, the proteins spent part of their trajectories in flow areas of damaging stress. Further examination showed that the history of the distribution of stresses applied on the vWF molecules, rather than the average, should be used to evaluate hydrodynamically-induced damage.

Fault detection and diagnosis in refrigeration systems using machine learning algorithms

The functionality of industrial refrigeration systems is important for environment-friendly companies and organizations, since faulty systems can impact human health by lowering food quality, cause pollution, and even lead to increased global warming. Therefore, in this industry, there is a high demand among manufacturers for early and automatic fault diagnosis. In this paper, different machine learning classifiers are tested to find the best solution for diagnosing twenty faults possibly encountered in such systems. All sensor faults and some relevant component faults are simulated in a high fidelity Matlab/Simscape model of the system, which has previously been used for controller development and verification. In this work, Convolutional Neural Networks, Support Vector Machines (SVM), Principal Components Analysis-SVM, Linear Discriminant Analysis-SVM, and Linear Discriminant Analysis classifiers are compared. The results indicate that the fault detection reliability of the algorithms highly depends on how well the training data covers the operation regime. Furthermore, it is found that a well-trained SVM can simultaneously classify twenty types of fault with 95% accuracy when the verification data is taken from different system configurations.

Tunable mode-locked Tm-doped fiber laser based upon cross-phase modulation.

We demonstrate the generation of soliton and dissipative soliton in an ultrafast thulium (Tm) doped fiber laser based upon cross-phase modulation (XPM) induced mode-locking. The mode-locking is realized by periodically modulating the 2-µm signal through XPM that is activated by an injected 1.5-µm pulsed laser. Such a mechanism enables the laser to be mode-locked in various operation regimes without any real or artificial saturable absorbers. Thanks to the XPM pulling effect, the wavelength of the Tm-doped fiber laser can be tuned by adjusting the repetition frequency of the 1.5-µm pulsed laser. The maximum tuning ranges achieved in this work for the soliton and dissipative soliton regimes are respectively 11 nm and 15 nm. The outcomes of this work not only provide a continuously and controllably wavelength-tunable ultrafast laser but also offer a passively synchronized dual-color fiber laser system, which is promised for many important applications such as Raman spectroscopy, nonlinear frequency conversion systems, and multi-color pump-probe systems.

НАУКОВО-ТЕХНІЧНЕ ЗАБЕЗПЕЧЕННЯ ОРГАНІЗАЦІЇ РОБОТИ ОЕС УКРАЇНИ В СИНХРОННОМУ РЕЖИМІ З ЄВРОПЕЙСЬКОЮ КОНТИНЕНТАЛЬНОЮ ЕНЕРГЕТИЧНОЮ СИСТЕМОЮ ENTSO-E

Scientific developments, which have been implemented as mandatory to provide a synchronous operation of IPS of Ukraine with the Continental European Power System ENTSO-E are presented. Firstly, it concerns a new level of information maintenance that has been realized by the creation and implementation of a wide range of specialized devices. The features of the construction of information-diagnostic devices are determined. The systems focused on the use of active elements, such as devices and technologies to provide flexible changes in network characteristics, as well as the implementation of electricity conversion to optimize their operation regimes are considered. A special attention was paid to providing a stable operation of the Ukrainian power system, including voltage stability. It covers tools and technologies used to create flexible AC transmission lines. The scenarios for eliminating a major system breakdown with an active power deficit of 1000 MW and other scenarios have been studied. The ways of further research on the development of IPS of Ukraine in the postwar period at the first stages of synchronous operation with ENTSO-E are identified. The paper identifies priority measures and tools aimed to improve the survivability and reliable control of the Ukrainian power system, development of principles and means of adaptation and reconstruction of emergency automatic control of electrical regimes and stability, creating prerequisites for digitalization of the power system. References 35, figures 2.

Characterization and Verification of Trotterized Digital Quantum Simulation Via Hamiltonian and Liouvillian Learning

The goal of digital quantum simulation is to approximate the dynamics of a given target Hamiltonian via a sequence of quantum gates, a procedure known as Trotterization. The quality of this approximation can be controlled by the so called Trotter step, that governs the number of required quantum gates per unit simulation time. The stroboscopic dynamics generated by Trotterization is effectively described by a time-independent Hamiltonian, referred to as the Floquet Hamiltonian. In this work, we propose Floquet Hamiltonian learning to reconstruct the experimentally realized Floquet Hamiltonian order-by-order in the Trotter step. This procedure is efficient, i.e., it requires a number of measurements that scales polynomially in the system size, and can be readily implemented in state-of-the-art experiments. With numerical examples, we propose several applications of our method in the context of verification of quantum devices: from the characterization of the distinct sources of errors in digital quantum simulators to determining the optimal operating regime of the device. We show that our protocol provides the basis for feedback-loop design and calibration of new types of quantum gates. Furthermore it can be extended to the case of non-unitary dynamics and used to learn Floquet Liouvillians, thereby offering a way of characterizing the dissipative processes present in NISQ quantum devices.

Quantum Repeaters with Encoding on Nitrogen-Vacancy-Center Platforms

We investigate quantum repeater protocols that rely on three-qubit repetition codes using nitrogen-vacancy (NV) centers in diamond as quantum memories. NV centers offer a two-qubit register, corresponding to their electron and nuclear spins, which makes it possible to perform deterministic two-qubit operations within one NV center. For quantum repeater applications, we, however, need to do joint operations on two separate NV centers. Here, we study two NV-center based repeater structures that enable such deterministic joint operations. One structure offers less consumption of classical communication, at the cost of more computation overhead, whereas the other one relies on a fewer number of physical resources and operations. We assess and compare their performance for the task of secret key generation under the influence of noise and decoherence with current and near-term experimental parameters. We quantify the regimes of operation, where one structure outperforms the other, and find the regions where encoded quantum repeaters offer practical advantages over their non-encoded counterparts.

Multiqudit interactions in molecular spins

We study photon-mediated interactions between molecular spin qudits in the dispersive regime of operation. We derive from a microscopic model the effective interaction between molecular spins, including their crystal field anisotropy (i.e., the presence of non-linear spin terms) and their multi-level structure. Finally, we calculate the long time dynamics for a pair of interacting molecular spins using the method of multiple scales analysis. This allows to find the set of 2-qudit gates that can be realized for a specific choice of molecular spins and to determine the time required for their implementation. Our results are relevant for the implementation of logical gates in general systems of qudits with unequally spaced levels or to determine an adequate computational subspace to encode and process the information.

4nπ Stable Multitasking Azapentacene: Acidochromism, Hole Mobility, and Visible Light Photoresponse.

Herein, we describe the synthesis, characterization, and optoelectronic investigation of a stable 4nπ dihydrotetraazapentacene derivative. The neutral dihydrotetraazapentacene contains a 24π-conjugated N-heteroacene core with two phenyl pendants appended thereof. The exceptional stability of this formally antiaromatic π-system is attributed to the fused dihydropyrazine ring, which has ethenamine (enamine) conjugations, and hence, the π-electrons delocalize over the nearly planar azapentacene core to endow with a global aromatic characteristic. The embedded dihydropyrazine also offers an additional Clar's sextet with enhanced aromaticity. The present dihydrotetraazapentacene can be considered as a multitasking N-heteroacene, which showed photoresponsive nature under visible light illumination, acidochromism in solution, and p-type charge transport with an appreciable field-effect hole mobility of 0.02 cm2 V-1 s-1 and a bulk p-type mobility of 0.98 × 10-4 cm2 V-1 s-1 in the space charge-limited regime of operation measured in the hole-only device. Nucleus-independent chemical shift calculation, anisotropy of the induced current density plot, and anisotropic mobility calculation were performed to support the experimental findings.