We experimentally and theoretically explored the microstructure-related effects of water and specimen size on the tensile strength of coal. Cylindrical coal specimens with different sizes (diameters of 25, 38, and 50 mm) and water contents (immersion time lengths: 0, 4, and 7 days) were processed. The microscopic features and mineral compositions of the coal samples were imaged and characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The physicochemical effects of water on the microstructures and coal matrices were investigated by acoustic emission (AE) and fractal theory. In this research, the tensile strength was found to be reduced in larger specimens, which can be explained by an exponential correlation. Water enhances the scale effect on the tensile strength of coal, although the water content decreases in larger specimens. Meanwhile, greater reductions in tensile strength were observed under the coupled effects of the water and specimen size. Based on... [more]

The main objective of this work is to contribute to a gradual replacement process of fossil diesel (D) with biofuels composed by diethyl carbonate (DEC) and either sunflower or castor oil, as straight vegetable oils (SVOs). DEC is a very interesting candidate as an oxygenated additive not only because of its low price and renewable nature, but also its favorable fuel properties, such as very low kinematic viscosity, high cetane number, high oxygen content, rich cold flow properties and good miscibility with fossil diesel and vegetable oils. In this work, the more suitable DEC/SVO biofuels are chosen based on kinematic viscosity, according to the European normative. Additionally, the most relevant physical−chemical properties of (bio)fuels such as density, calorific value, cloud point, pour point and cetane number are determined. The influence of DEC on engine performance and exhaust emissions is analyzed by fueling a conventional Diesel engine with the different D/DEC/SVO triple and DE... [more]

This work investigates an innovative low-voltage (<60 V) hybrid device that enables engine boosting and downsizing in addition to mild hybrid functionalities such as regenerative braking, start-stop, and torque assist. A planetary gear set and a brake permit the power split supercharger (PSS) to share a 9 kW motor between supercharging the engine and direct torque supply to the crankshaft. In contrast, most e-boosting schemes use two separate motors for these two functionalities. This single motor structure restricts the PSS operation to only one of the supercharging or parallel hybrid modes; therefore, an optimized decision making strategy is necessary to select both the device mode and its power split ratio. An adaptive equivalent consumption minimization strategy (A-ECMS), which uses the battery state of charge (SoC) history to adjust the equivalence factor, is developed for energy management of the PSS. The A-ECMS effectiveness is compared against a dynamic programming (DP) solu... [more]

This paper presents the possibility of using Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs) instead of the conventional silicon metal oxide semiconductor field effect transistor (MOSFET) to implement a high-frequency intermediate bus converter (IBC) as part of a typical distributed power architecture used in a space power application. The results show that processing the power at greater frequencies is possible with a reduction in mass and without impacting the system efficiency. The proposed solution was experimentally validated by the implementation of a 1 MHz zero-voltage and zero-current switching (ZVZCS) current-fed half-bridge converter with synchronous rectification compared with the same converter using silicon as the standard technology on power switches and working at 100 kHz. In conclusion, the replacement of silicon (Si) transistors by GaN HEMTs is feasible, and GaN HEMTs are promising next-generation devices in the power electronics field and can coexist... [more]

Industrial exhausted heat can be used as the heat source of central heating for higher energy efficiency. To recover more industrial exhausted heat, a new low-temperature central heating system integrated with industrial exhausted heat using distributed electric compression heat pumps is put forward and analyzed from the aspect of thermodynamics and economics. The roles played by the distributed electric compression heat pumps in improving both thermal performance and financial benefit of the central heating system integrated with industrial exhausted heat are greater than those by the centralized electric compression heat pumps. The proposed low-temperature central heating system has higher energy efficiency, better financial benefit, and longer economical distance of transmitting exhausted heat, and thus, its configuration is optimal. For the proposed low-temperature central heating system, the annual coefficient of performance, annual product exergy efficiency, heating cost, and pay... [more]

Multiphase systems provides benefits compared to three-phase systems, such as improved torque per ampere, high power density, better fault tolerance, lower current per phase (due to power-splitting among a higher number of phases), and lower torque ripple, among others. Depending on the application, the system must meet determined requirements, such as the presence of harmonic content, power losses, and common-mode voltage (CMV) generation. This paper presents a comparative analysis of space vector modulation (SVM) techniques applied to a five-phase voltage source inverter with SiC switches to provide an overview of their performance. The performance of five-phase 2L SVPWM (space vector pulse width modulation), 2L+2M SVPWM, 4L SVPWM techniques, and their discontinuous versions, are analyzed by focusing on harmonic content, power losses, and CMV generation using SiC semiconductor devices. Matlab/Simulink and PLECS simulations are performed to achieve the above mentioned goal. The use of... [more]

The large-scale deployment of pervasive sensors and decentralized computing in modern smart grids is expected to exponentially increase the volume of data exchanged by power system applications. In this context, the research for scalable and flexible methodologies aimed at supporting rapid decisions in a data rich, but information limited environment represents a relevant issue to address. To this aim, this paper investigates the role of Knowledge Discovery from massive Datasets in smart grid computing, exploring its various application fields by considering the power system stakeholder available data and knowledge extraction needs. In particular, the aim of this paper is dual. In the first part, the authors summarize the most recent activities developed in this field by the Task Force on “Enabling Paradigms for High-Performance Computing in Wide Area Monitoring Protective and Control Systems” of the IEEE PSOPE Technologies and Innovation Subcommittee. Differently, in the second part,... [more]

The concept of virtual power plants (VPP) was introduced over 20 years ago but is still actively researched. The majority of research now focuses on analyzing case studies of such installations. In this article, the investigation is based on a VPP in Poland, which contains hydropower plants (HPP) and energy storage systems (ESS). For specific analysis, the power quality (PQ) issues were selected. The used data contain 26 weeks of multipoint, synchronic measurements of power quality levels in four related points. The investigation is concerned with the application of a global index to a single-point assessment as well as an area-related assessment approach. Moreover, the problem of flagged data is discussed. Finally, the assessment of VPP’s impact on PQ level is conducted.

A new optimization method for the assessment of the coefficients existing in a model of drying kinetics is developed and presented in this article. This method consists of matching the drying kinetics resulting from the mathematical model with the drying kinetics resulting from the experiments. Both the heat and mass transfer coefficients, the critical relative humidity, and the additional ultrasound energy (heat) source are included in the optimization procedure. The Adams−Bashforth multistep method of solving nonlinear ordinary differential equations is used. The inverse problem of model parameter estimation is solved by the Rosenbrock optimization method. The methodology is illustrated by the example of the ultrasound-assisted convective drying of apple and carrot. A high level of agreement between the results obtained experimentally and numerically was found. The obtained results confirmed the great influence of ultrasound on the drying kinetics. It was found that ultrasound applic... [more]

Energy recovery from a low temperature heat source using heat pump technology is becoming a popular application. The domestic hot water demand has the characteristic of being very irregular along the day, with periods in which the demand is very intensive and long periods in which it is quite small. In order to use heat pumps for this kind of applications efficiently, the proper sizing and design of the water storage tank is critical. In this work, the optimal sizing of the two possible tank alternatives, closed stratified tank and variable-water-volume tank, is presented, and their respective performance compared, for domestic hot water production based on low temperature energy recovery in two potential applications (grey water and ultra-low temperature district heating). The results show that the efficiency of these kind of systems is very high and that variable-water-volume tanks allow a better use of the energy source, with an 8% higher exergy efficiency and around 3% better seaso... [more]

Potential leakage of reservoir fluids is considered a key risk factor for geologic CO2 sequestration (GCS), with concerns of their chemical impacts on the quality of overlying underground sources of drinking water (USDWs). Effective risk assessment provides useful information to guide GCS activities for protecting USDWs. In this study, we present a quantified risk assessment case study of an active commercial-scale CO2-enhanced oil recovery (CO2-EOR) and sequestration field, the Farnsworth Unit (FWU). Specific objectives of this study include: (1) to quantify potential risks of CO2 and brine leakage to the overlying USDW quality with response surface methodology (RSM); and (2) to identify water chemistry indicators for early detection criteria. Results suggest that trace metals (e.g., arsenic and selenium) are less likely to become a risk due to their adsorption onto clay minerals; no-impact thresholds based on site monitoring data could be a preferable reference for early groundwater... [more]

Current transportation systems contributed to one quarter to the Greenhouse Gases (GhG) emissions and the mobility demand increases continuously. The transportation infrastructure design has to be optimized to mitigate these emissions. The methodology “Sloop” (acronym for Slope Optimization) has recently been set up to optimize the longitudinal road profile with respect to a Global Warming Potential (GWP) criterion calculated for both the construction and operational phases while incorporating accurate vehicle models. This paper proposes a customized optimization strategy that significantly improves the Sloop methodology. From an initial longitudinal profile generated by road designers, our algorithm identifies the optimized profile in terms of GWP. This optimization step is complex due to the large number of degrees of freedom, along with various constraints to obtaining a feasible solution and the computational cost of the operational phase assessment. The most stringent constraint e... [more]

Biofuels as alternative fuels in today’s world are becoming increasingly important for the reduction of greenhouse gases. Here, we present and evaluate the potential of a new alternative fuel based on the conversion of medium-chain fatty acids to biojet (MBJ), which was produced from coconut oil using hydrotreated processes. MBJ is produced by using both deoxygenation and isomerization processes. Several blends of this type of biojet fuel with Jet A-1 were run in a gas-turbine engine (Rover 1S/60, ROTAX LTD., London, England) for the purpose of investigating engine performance and emissions. Performance results showed almost the same results as those of Jet A-1 fuel for these fuels in terms of thermal efficiency, brake-specific fuel consumption, turbine-inlet temperature, and exhaust-gas temperature. The results of exhaust-gas emissions also showed no significant effects on carbon monoxide, unburned hydrocarbon, and nitrogen oxides, while a decrease in smoke opacity was found when blen... [more]

The double-wall structure is one of the most effective cooling techniques used in many engineering applications, such as turbine vane/blade, heat exchangers, etc. Heat transfer on the internal surfaces of a double-wall structure was studied at impinging Reynolds numbers ranging from 1 × 104 to 6 × 104 using the transient thermochromic liquid crystal (TLC) technique. The two-dimensional distributions of Nusselt numbers and their averaged values were obtained on the impingement surface, target surface and the pin fin surface. The Nusselt number correlations on the surfaces mentioned above were determined as a function of Reynolds number. The results show that the second peak values of the Nusselt number distribution appear on the target surface at all Reynolds numbers studied in this paper for a short distance of the target surface to impingement surface. This phenomenon becomes significant with the further increase of the Reynolds number. The difference between the Nusselt number at the... [more]

Automotive high-voltage busbars are critical electrical components in electric vehicle battery systems as they connect individual battery modules and form the connection to the vehicle’s powertrain. Therefore, a vehicle crash can pose a significant risk to safety by compromising busbar insulation, leading to electrical short circuits inside the battery. In turn, these can trigger thermal chain reactions in the cell modules of the battery pack. In order to ensure a safe design in future applications of busbars, this study investigated the mechanical behavior of busbars and their insulation. Our results indicated that crashlike compressive and bending loads lead to complex stress states resulting in failure of busbar insulation. To estimate the safety of busbars in the early development process using finite element simulations, suitable material models were evaluated. Failure of the insulation was included in the simulation using an optimized generalized incremental stress state dependen... [more]

Image-based evaluation methods are a valuable tool for source rock characterization. The time and resources needed to obtain images has spurred development of machine-learning generative models to create synthetic images of pore structure and rock fabric from limited image data. While generative models have shown success, existing methods for generating 3D volumes from 2D training images are restricted to binary images and grayscale volume generation requires 3D training data. Shale characterization relies on 2D imaging techniques such as scanning electron microscopy (SEM), and grayscale values carry important information about porosity, kerogen content, and mineral composition of the shale. Here, we introduce RockFlow, a method based on generative flow models that creates grayscale volumes from 2D training data. We apply RockFlow to baseline binary micro-CT image volumes and compare performance to a previously proposed model. We also show the extension of our model to 2D grayscale dat... [more]

The application of a catalyst on a surface inside a combustion chamber is known as a supplementary method of exhaust gas aftertreatment. The efficiency of this method in the reduction in exhaust emissions as well as its influence on other engine properties has been analyzed in multiple scientific works. Most often, these works present the results of investigations carried out on dynamometers under engine stationary conditions. There are no results of the catalyst investigations performed under dynamic states, particularly on-going real time analyses during engine operation. Therefore, the authors set out to explore the efficiency of the in-cylinder catalyst of a diesel engine under dynamic conditions simulating actual vehicle operation. A unique methodology was applied. The investigations were carried out in road conditions in a test simulating the New European Driving Cycle (NEDC) homologation test in compliance with the similarity criteria of the zero-dimensional characteristics of v... [more]

Distributed energy resource (DER) has been widely deployed, and distributed generation (DG) can complement the distribution system. Favorable DG deployment provides the grid-connected microgrid (MG) with stable voltage and reduces emission and power generation costs. DGs are considered distributed feeders, and MG is required to be operated under the optimal state. Reconfiguration is a practical approach to optimizing resource allocation. The optimal global solution is obtained via optimization algorithms. In this paper, three objectives are defined, namely, minimization of economic cost (ECC), emission cost (EMC), and voltage deviation (VD). Consequently, a fuzzy moth-flame optimization (FMFO) algorithm is proposed to coordinate the interests of multiple objectives. Moreover, the simulation is conducted based on the standard IEEE 33-bus radial distribution system (RDS), under which the impact of deployment of various DG type and quantity on the MG is explored. In particular, diverse DG... [more]

Microsupercapacitors have attracted significant attention due to several of their advantageous characteristics such as lightweight, small volume, and planar structure that is favorable for high mechanical flexibility. Among the various micro supercapacitor forms, those with laser-induced graphene (LIG) electrodes are promising as flexible energy storage devices. While LIG microelectrodes can be fabricated simply by direct laser writing, the capacitance and energy density of these devices are limited because of the relatively low density of LIG, which leads to low surface areas. These limitations could be overcome by densifying the LIG. Here, we report the use of densified laser-induced graphene (d-LIG) to fabricate flexible micro supercapacitors. Interdigitated d-LIG electrodes were prepared by duplicate laser pyrolysis of a polyimide sheet by using a CO2 laser. A PVA-H2SO4 gel-type electrolyte was then applied to the d-LIG electrode surface to assemble a d-LIG micro supercapacitor. Th... [more]

In this paper, we propose a novel charge-equalization circuit for series-connected batteries. The circuit is composed of an intermediate resonant energy tank, formed by an inductor and a capacitor, and selection switches connected to each battery. The advantage of the proposed circuit is that an exchange of unbalanced charge can be established between any two batteries via the intermediate energy tank. In addition, more than one adjacent battery can serve as a charge-transference party on either side through proper activation of the associated selection switches. Moreover, by virtue of the resonant tank, zero-current switching can be achieved to significantly reduce the transference losses. A laboratory circuit with a control unit was designed for eight 2.5 Ah lithium iron phosphate (LiFePO4) batteries in series. The test results demonstrate that the proposed charge-equalization circuit can realize charge balance effectively. With the charge-equalization circuit, the worst open-circuit... [more]

Drifting away from the neoclassical growth conjecture of economic growth being solely dependent on capital and labor inputs, this paper aimed to evaluate the dynamic impacts of energy consumption, energy prices and imported energy-dependency on both gross and sectoral value-added figures of Sri Lanka. The analysis has particularly used the robust econometric methods that can account for structural break issues in the data. The results, in a nutshell, indicated that energy consumption homogeneously contributes to gross, agricultural, industrial and services value-additions in Sri Lanka. However, positive oil price shocks and greater shares of imported energy in the total energy consumption figures are found to dampen the growth figures, especially in the context of the gross, industrial and services value additions. Besides, the joint growth-inhibiting impacts of oil price movements and energy import-dependency are also ascertained. On the other hand, the causality estimates reveal bidi... [more]

Physico-chemical properties of diethyl ether/linseed oil (DEE/LO) fuel blends were empirically tested in this article for the first time. In particular, kinematic viscosity (ν), density (ρ), lower heating value (LHV), cold filter plugging point (CFPP) and surface tension (σ) were examined. For this research diethyl ether (DEE) was blended with linseed oil (LO) in volumetric ratios of 10%, 20% and 30%. Obtained results were compared with literature data of diethyl ether/rapeseed oil (DEE/RO) fuel blends get in previous research in such a way looking on differences also between oil types. It was found that DEE impacts significantly on the reduction of plant oil viscosity, density and surface tension and improve low temperature properties of tested oils. In particular, the addition of 10% DEE to LO effectively reduces its kinematic viscosity by 53% and even by 82% for the blend containing 30% DEE. Tested ether reduces density and surface tension of LO up to 6% and 25% respectively for the... [more]

The need for flexibility in power system operation gradually increases regarding more renewable energy integration, load growth, etc., and the system operators already invest in this manner to enhance the power system operation. Besides, the power system has thermally sensitive assets such as lines, transformers, etc. that are normally operated under highly conservative static ratings. There is a growing trend in this regard to use the actual capacity of such assets dynamically under varying operating conditions leading to a dynamic thermal rating concept which is referred as dynamic line rating (DLR) approach specifically for lines. This study provides a comprehensive overview of existing perspectives on DLR and combination with other flexibility options from an operational point of view. Apart from the existing review studies more focused on implementation category of DLR concept, the concentration on more operational stage from the power system operation point of view leads the diff... [more]

Electrolyte-supported solid oxide cells are often used for steam electrolysis. Advantages are high mechanical stability and a low degradation rate. The aim of this proof of concept study was to use a femtosecond laser to process the electrolyte of an electrolyte-supported solid oxide cell and evaluate the effect of this laser treatment on the electrochemical performance. The femtosecond laser treatment induces a macroscopic and a superimposed microscopic structure. It can be proven that the electrolyte remains gas tight and the electrochemical performance increases independently of the laser parameters. The initial area-specific resistance degradation during a constant current measurement of 200 h was reduced from 7.9% for a non-treated reference cell to 3.2% for one of the laser-treated cells. Based on electrochemical impedance measurements, it was found that the high frequency resistance of the laser-treated cells was reduced by up to 20% with respect to the reference cell. The imped... [more]

Occupant behavior and business processes in a building environment constitute an inseparable set of important factors that drives energy consumption. Existing methodologies for building energy management lag behind in addressing these core parameters by focusing explicitly on the building’s structural components. Additional layers of information regarding indoor and outdoor environmental conditions and occupant behavior patterns, mostly driven by everyday business processes (schedules, loads, and specific business activities related to occupancy patterns and building operations), are necessary for the effective and efficient modeling of building energy performance in order to establish a holistic energy efficiency management framework. The aim of this paper was to develop a context-driven framework in which multiple levels of information regarding occupant behavior patterns resulting from everyday business processes were incorporated for efficient energy management in buildings. A prel... [more]