Previous Issue

E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Table of Contents

Energies, Volume 12, Issue 10 (May-2 2019)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-166
Export citation of selected articles as:
Open AccessArticle
An Overview of the Influence of Biodiesel, Alcohols, and Various Oxygenated Additives on the Particulate Matter Emissions from Diesel Engines
Energies 2019, 12(10), 1987; https://doi.org/10.3390/en12101987 (registering DOI)
Received: 13 April 2019 / Revised: 18 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (1569 KB) | HTML Full-text | XML Full-text
Abstract
Rising pollution levels resulting from vehicular emissions and the depletion of petroleum-based fuels have left mankind in pursuit of alternatives. There are stringent regulations around the world to control the particulate matter (PM) emissions from internal combustion engines. To this end, researchers have [...] Read more.
Rising pollution levels resulting from vehicular emissions and the depletion of petroleum-based fuels have left mankind in pursuit of alternatives. There are stringent regulations around the world to control the particulate matter (PM) emissions from internal combustion engines. To this end, researchers have been exploring different measures to reduce PM emissions such as using modern combustion techniques, after-treatment systems such as diesel particulate filter (DPF) and gasoline particulate filter (GPF), and alternative fuels. Alternative fuels such as biodiesel (derived from edible, nonedible, and waste resources), alcohol fuels (ethanol, n-butanol, and n-pentanol), and fuel additives have been investigated over the last decade. PM characterization and toxicity analysis is still growing as researchers are developing methodologies to reduce particle emissions using various approaches such as fuel modification and after-treatment devices. To address these aspects, this review paper studies the PM characteristics, health issues, PM physical and chemical properties, and the effect of alternative fuels such as biodiesel, alcohol fuels, and oxygenated additives on PM emissions from diesel engines. In addition, the correlation between physical and chemical properties of alternate fuels and the characteristics of PM emissions is explored. Full article
Figures

Figure 1

Open AccessArticle
Local Energy Storage and Stochastic Modeling for Ultrafast Charging Stations
Energies 2019, 12(10), 1986; https://doi.org/10.3390/en12101986 (registering DOI)
Received: 8 April 2019 / Revised: 3 May 2019 / Accepted: 17 May 2019 / Published: 23 May 2019
PDF Full-text (1323 KB)
Abstract
Multi-stall fast charging stations are often thought to require megawatt-range grid connections. The power consumption profile of such stations results in high cost penalties due to monthly power peaks and expensive linkage fees. A local energy storage system (ESS) can be used to [...] Read more.
Multi-stall fast charging stations are often thought to require megawatt-range grid connections. The power consumption profile of such stations results in high cost penalties due to monthly power peaks and expensive linkage fees. A local energy storage system (ESS) can be used to address peak power demands. However, no appropriate sizing method is available to match specific constraints, such as the contracted power available from the grid and the projected recharging demand. A stochastic distribution of charging events was used in this paper to model power demand profiles at the station, with a one minute resolution. Based on 100 simulated months, we propose an optimum number of charging points, and we developed an algorithm to return the required local ESS capacity as a function of the available grid connection. The role of ESSs in the range of 100 kWh to 1 MWh was studied for all stations with up to 2000 charging events per week. The relevance of ESS implementation was assessed along three parameters: the number of charging points, the available grid connection, and the ESS capacity. This work opens new possibilities for multi-stall charging station deployment in locations with limited access to the medium voltage grid, and provides sizing guidelines for effective ESSs implementation. In addition, it helps build business cases for charging station operators in regions with high demand charges. Full article
(This article belongs to the Section Electric Vehicles)
Open AccessArticle
Modeling and Mechanism Investigation of Inertia and Damping Issues for Grid-Tied PV Generation Systems with Droop Control
Energies 2019, 12(10), 1985; https://doi.org/10.3390/en12101985 (registering DOI)
Received: 23 April 2019 / Revised: 17 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (6500 KB) | HTML Full-text | XML Full-text
Abstract
Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high [...] Read more.
Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high proportional GPVGS, are not yet clear. Therefore, this paper takes the GPVGS based on droop control as the research object. Focusing on the DC voltage control (DVC) timescale dynamics, the mathematical model of the GPVGS is firstly established. Secondly, the electrical torque analysis method is used to analyze the influence law of inertia, damping and synchronization characteristics from the physical mechanism perspective. The research finds that the equivalent inertia, damping and synchronization coefficient of the system are determined by the control parameters, structural parameters and steady-state operating point parameters. Changing the control parameters is the simplest and most flexible way to influence the inertia, damping and synchronization ability of the system. The system inertia is influenced by the DC voltage outer loop proportional coefficient Kp and enhanced with the increase of Kp. The damping characteristic of the system is affected by the droop coefficient Dp and weakened with the increase of Dp. The synchronization effect is only controlled by DC voltage outer loop integral coefficient Ki and enhanced with the increase of Ki. In addition, the system dynamic is also affected by the structural parameters such as line impedance X, DC bus capacitance C, and steady-state operating point parameters such as the AC or DC bus voltage level of the system and steady-state operating power (power angle). Finally, the correctness of the above analysis are verified by the simulation and experimental results. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
Figures

Figure 1

Open AccessArticle
A General Transformer Evaluation Method for Common-Mode Noise Behavior
Energies 2019, 12(10), 1984; https://doi.org/10.3390/en12101984 (registering DOI)
Received: 29 April 2019 / Revised: 17 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (6256 KB) | HTML Full-text | XML Full-text
Abstract
In isolated power converters, the transformer is a key part of voltage transformation and isolation. Since common-mode (CM) noise is rather difficult to suppress compared with different-mode (DM) noise, more and more scholars are paying attention to the characteristics of CM noise, especially [...] Read more.
In isolated power converters, the transformer is a key part of voltage transformation and isolation. Since common-mode (CM) noise is rather difficult to suppress compared with different-mode (DM) noise, more and more scholars are paying attention to the characteristics of CM noise, especially in high-frequency CM noise behaviors. CM noise can be further divided into conducted CM noise and radiated CM noise, and the main focus of this paper is on conducted CM noise. The CM coupling capacitance of the transformer is one of the main contributors of CM noise, which has been verified in many previous studies. Hence, eliminating the CM noise in a transformer coupling path can significantly lower the whole CM noise level of the converter. Professional conducted electromagnetic interference (EMI) testing instruments are quite expensive. In this paper, a general transformer evaluation technique for CM noise behavior is proposed. Only a signal generator and oscilloscope can achieve transformer CM noise behavior evaluation. PCB planar flyback transformers are designed, and a series of noise spectrums and voltage waveforms can verify the effectiveness of the proposed transformer evaluation method. The flyback adapter porotype can pass the EMI standard limited line EN55022 class B by the proposed evaluation method. Full article
(This article belongs to the Special Issue Power Transformer Condition Assessment)
Figures

Graphical abstract

Open AccessArticle
Design and Control of a Permanent Magnet RotLin Motor for New Foldable Photovoltaic Units
Energies 2019, 12(10), 1983; https://doi.org/10.3390/en12101983 (registering DOI)
Received: 7 April 2019 / Revised: 15 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (9066 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a new permanent magnet rotary-linear (RotLin) motor is proposed for foldable photovoltaic units. Firstly, the mechanical structure, operation principles and magnetic circuits of the motor are introduced, and a design procedure elaborated the parameters calculation in the linear part and [...] Read more.
In this study, a new permanent magnet rotary-linear (RotLin) motor is proposed for foldable photovoltaic units. Firstly, the mechanical structure, operation principles and magnetic circuits of the motor are introduced, and a design procedure elaborated the parameters calculation in the linear part and the rotary part. Finite element method (FEM) is used to analyze the magnetic field of the motor, and linear force outputs and torque outputs are obtained. Secondly, a control scheme is designed for the prototype of the motor including the position control and the speed control. The deformation on the mover and the magnetic coupling effect between the linear part and the rotational part are discussed. Finally, experimental results show that this motor can simultaneously realize a linear movement with continuous rotation. The linear poisoning accuracy can achieve 0.4 µm and the angular speed can be controlled with steady errors less than 3 rpm, proving the effectiveness of the proposed RotLin motor. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
Figures

Figure 1

Open AccessArticle
A Text-Mining Approach to Assess the Failure Condition of Wind Turbines Using Maintenance Service History
Energies 2019, 12(10), 1982; https://doi.org/10.3390/en12101982 (registering DOI)
Received: 2 April 2019 / Revised: 7 May 2019 / Accepted: 16 May 2019 / Published: 23 May 2019
PDF Full-text (884 KB) | HTML Full-text | XML Full-text
Abstract
Detecting and determining which systems or subsystems of a wind turbine have more failures is essential to improve their design, which will reduce the costs of generating wind power. Two of the most critical failures, the generator and gearbox, are analyzed and characterized [...] Read more.
Detecting and determining which systems or subsystems of a wind turbine have more failures is essential to improve their design, which will reduce the costs of generating wind power. Two of the most critical failures, the generator and gearbox, are analyzed and characterized with four metrics. This failure analysis usually begins with the identification of the turbine’s condition, a process normally performed by an expert examining the wind turbine’s service history. This is a time-consuming task, as a human expert has to examine each service entry. To automate this process, a new methodology is presented here, which is based on a set of steps to preprocess and decompose the service history to find relevant words and sentences that discriminate an unhealthy wind turbine period from a healthy one. This is achieved by means of two classifiers fed with the matrix of terms from the decomposed document of the training wind turbines. The classifiers can extract essential words and determine the conditions of new turbines of unknown status using the text from the service history, emulating what a human expert manually does when labelling the training set. Experimental results are promising, with accuracy and F-score above 90% in some cases. Condition monitoring system can be improved and automated using this system, which helps the expert in the tedious task of identifying the relevant words from the turbine service history. In addition, the system can be retrained when new knowledge becomes available and may therefore always be as accurate as a human expert. With this new tool, the expert can focus on identifying which systems or subsystems can be redesigned to increase the efficiency of wind turbines. Full article
(This article belongs to the Special Issue Design, Fabrication and Performance of Wind Turbines)
Figures

Figure 1

Open AccessArticle
Spatio-Temporal Model for Evaluating Demand Response Potential of Electric Vehicles in Power-Traffic Network
Energies 2019, 12(10), 1981; https://doi.org/10.3390/en12101981 (registering DOI)
Received: 23 April 2019 / Revised: 17 May 2019 / Accepted: 18 May 2019 / Published: 23 May 2019
PDF Full-text (4591 KB) | HTML Full-text | XML Full-text
Abstract
Electric vehicles (EVs) can be regarded as a kind of demand response (DR) resource. Nevertheless, the EVs travel behavior is flexible and random, in addition, their willingness to participate in the DR event is uncertain, they are expected to be managed and utilized [...] Read more.
Electric vehicles (EVs) can be regarded as a kind of demand response (DR) resource. Nevertheless, the EVs travel behavior is flexible and random, in addition, their willingness to participate in the DR event is uncertain, they are expected to be managed and utilized by the EV aggregator (EVA). In this perspective, this paper presents a composite methodology that take into account the dynamic road network (DRN) information and fuzzy user participation (FUP) for obtaining spatio-temporal projections of demand response potential from electric vehicles and the electric vehicle aggregator. A dynamic traffic network model taking over the traffic time-varying information is developed by graph theory. The trip chain based on housing travel survey is set up, where Dijkstra algorithm is employed to plan the optimal route of EVs, in order to find the travel distance and travel time of each trip of EVs. To demonstrate the uncertainties of the EVs travel pattern, simulation analysis is conducted using Monte Carlo method. Subsequently, we suggest a fuzzy logic-based approach to uncertainty analysis that starts with investigating EV users’ subjective ability to participate in DR event, and we develop the FUP response mechanism which is constructed by three factors including the remaining dwell time, remaining SOC, and incentive electricity pricing. The FUP is used to calculate the real-time participation level of a single EV. Finally, we take advantage of a simulation example with a coupled 25-node road network and 54-node power distribution system to demonstrate the effectiveness of the proposed method. Full article
Figures

Figure 1

Open AccessArticle
Post-Closure Performance Assessment for Deep Borehole Disposal of Cs/Sr Capsules
Energies 2019, 12(10), 1980; https://doi.org/10.3390/en12101980 (registering DOI)
Received: 23 April 2019 / Revised: 10 May 2019 / Accepted: 15 May 2019 / Published: 23 May 2019
PDF Full-text (2509 KB) | HTML Full-text | XML Full-text
Abstract
Post-closure performance assessment (PA) calculations suggest that deep borehole disposal of cesium (Cs)/strontium (Sr) capsules, a U.S. Department of Energy (DOE) waste form (WF), is safe, resulting in no releases to the biosphere over 10,000,000 years when the waste is placed in a [...] Read more.
Post-closure performance assessment (PA) calculations suggest that deep borehole disposal of cesium (Cs)/strontium (Sr) capsules, a U.S. Department of Energy (DOE) waste form (WF), is safe, resulting in no releases to the biosphere over 10,000,000 years when the waste is placed in a 3–5 km deep waste disposal zone. The same is true when a hypothetical breach of a stuck waste package (WP) is assumed to occur at much shallower depths penetrated by through-going fractures. Cs and Sr retardation in the host rock is a key control over movement. Calculated borehole performance would be even stronger if credit was taken for the presence of the WP. Full article
(This article belongs to the Special Issue Deep Borehole Disposal of Nuclear Waste)
Figures

Figure 1

Open AccessArticle
Enhanced Threshold Point Calculation Algorithm for Switch Fault Diagnosis in Grid Connected 3-Phase AC–DC PWM Converters
Energies 2019, 12(10), 1979; https://doi.org/10.3390/en12101979 (registering DOI)
Received: 6 May 2019 / Revised: 20 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
PDF Full-text (3643 KB) | HTML Full-text | XML Full-text
Abstract
The resilience of systems with alternating current (AC)–direct current (DC) converters has been investigated with the aim of improving switch fault diagnosis. To satisfy this aim, this paper proposes a switch fault diagnosis algorithm for three-phase AC–DC converters. The proposed algorithm operates using [...] Read more.
The resilience of systems with alternating current (AC)–direct current (DC) converters has been investigated with the aim of improving switch fault diagnosis. To satisfy this aim, this paper proposes a switch fault diagnosis algorithm for three-phase AC–DC converters. The proposed algorithm operates using the phase current instead of the average current to reduce the calculation time required for fault switch detection. Moreover, a threshold point calculation method is derived using a theoretical analysis, which was lacking in previous research. Using the calculated threshold point, a switch fault diagnosis algorithm is obtained to detect faults independent of the load condition. Using the proposed algorithm, switch faults can be detected within 4 ms, which is the recommended value for uninterruptible power supply (UPS). The theoretical analysis, the operating principle, and the experimental results on a 3-kW grid-tied AC–DC converter test-bed are presented herein, which verify the performance of the proposed algorithm. Full article
(This article belongs to the Special Issue Fault Diagnosis and Fault-Tolerant Control)
Figures

Figure 1

Open AccessArticle
Spatial Analysis of Residual Biomass and Location of Future Storage Centers in the Southwest of Europe
Energies 2019, 12(10), 1978; https://doi.org/10.3390/en12101978 (registering DOI)
Received: 5 April 2019 / Revised: 14 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (4076 KB) | HTML Full-text | XML Full-text
Abstract
Forests can be exploited for obtaining biomass, which belongs to a bioenergy group with great energy potential that could replace fossil fuels. This article presents a novel procedure to quantify, map and define biomass, which takes into account both environmental and economic issues. [...] Read more.
Forests can be exploited for obtaining biomass, which belongs to a bioenergy group with great energy potential that could replace fossil fuels. This article presents a novel procedure to quantify, map and define biomass, which takes into account both environmental and economic issues. With regard to the environment, only the annual growth of tree species is considered, and not the previous stocks. The growth is determined by logarithmic equations through an original procedure supported by a biomass estimator, which represents the amount of biomass generated annually for energy use, and by means of Excel tables, the exploitable biomass values are obtained. Previously, and by using GIS, areas with slopes exceeding 20% are discarded, thus avoiding soil erosion and damage, and in any case that biomass is not extracted for economic reasons. The same procedure is followed, discarding those areas located more than 4 km from forest roads and runways, as transport costs are increased. Finally, those layers with low energy potential are eliminated as well. Therefore, annually selected quantities of biomass can be obtained safely and abundantly by using detailed distribution maps of the resources, and through planning and performing efficient forestry extraction works. Full article
(This article belongs to the Section Bio-Energy)
Figures

Figure 1

Open AccessArticle
Experimental and Numerical Investigation of Bubble–Bubble Interactions during the Process of Free Ascension
Energies 2019, 12(10), 1977; https://doi.org/10.3390/en12101977 (registering DOI)
Received: 10 March 2019 / Revised: 13 May 2019 / Accepted: 14 May 2019 / Published: 23 May 2019
PDF Full-text (4636 KB) | HTML Full-text | XML Full-text
Abstract
The shape and rising behavior of the horizontally arranged twin bubbles in a steady liquid are experimentally studied employing high-speed photography and digital image processing, and numerically studied by the Volume-Of-Fluid (VOF) method, in combination with a momentum equation coupled with a surface [...] Read more.
The shape and rising behavior of the horizontally arranged twin bubbles in a steady liquid are experimentally studied employing high-speed photography and digital image processing, and numerically studied by the Volume-Of-Fluid (VOF) method, in combination with a momentum equation coupled with a surface tension model. The movement trajectory and the velocity variation in horizontal and vertical directions of the horizontally arranged twin bubbles rising side by side, as observed in experiments, are described. According to the results, when two bubbles rise side by side, their horizontal velocity changes by the simple harmonic law; there is a cyclical process of two bubbles repeatedly attracted to and bounced against each other, rather than at constant distance between each other, and the bubbles swing up and down periodically in the water. The mathematical model and its numerical implementation are presented in detail. The validation of the model is confirmed by comparing the numerical and experimental results, which are in good agreement with each other; the numerical simulation can accurately reproduce the deformation, attraction, and repulsion of the bubble pairs. The phenomenon of attraction and repulsion is comprehensively analyzed from the viewpoint of a flow field. It is considered that the interaction between the bubbles is mainly influenced by the changes of the flow field due to vortex counteraction and wake merging effects. Full article
Figures

Figure 1

Open AccessArticle
A Multi-Scale Analysis of the Fire Problems in an Urban Utility Tunnel
Energies 2019, 12(10), 1976; https://doi.org/10.3390/en12101976 (registering DOI)
Received: 4 April 2019 / Revised: 11 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
PDF Full-text (7427 KB) | HTML Full-text | XML Full-text
Abstract
Building utility tunnels has been widely adopted as an important solution for the sustainable development of cities, but their unique fire problems have not attracted enough attention to date. With the purpose of preliminarily understanding the fire phenomena in a utility tunnel, this [...] Read more.
Building utility tunnels has been widely adopted as an important solution for the sustainable development of cities, but their unique fire problems have not attracted enough attention to date. With the purpose of preliminarily understanding the fire phenomena in a utility tunnel, this study performed a comprehensive analysis, including the burning behaviour of accommodated cables, hot gas temperature field and enhanced fuel burning rates based on bench-scale, full-scale and model-scale fire tests. The critical exposed radiative heat flux for the 10-kV power cable to achieve complete burning was identified. The whole burning process was divided into five phases. The cable’s noteworthy hazards and dangerous fire behaviours were also examined. The two-dimensional (2D) gas temperature fields and longitudinal maximum temperature distributions were investigated carefully, after which a versatile model was derived. The model predicted the maximum temperature attenuation of both upstream and downstream flows reasonably well. Finally, the phenomenon of enhanced fuel burning was explored. A multivariate cubic function that considers the global effects of relative width, height and distance was further proposed to estimate the enhancement coefficient. The current findings can provide designers and operators with valuable guidance for the integrated promotion of utility tunnels’ fire safety level. Full article
Figures

Figure 1

Open AccessArticle
Experimental Study on Reducing CO2–Oil Minimum Miscibility Pressure with Hydrocarbon Agents
Energies 2019, 12(10), 1975; https://doi.org/10.3390/en12101975 (registering DOI)
Received: 8 April 2019 / Revised: 28 April 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
PDF Full-text (3553 KB) | HTML Full-text | XML Full-text
Abstract
CO2 flooding is an important method for improving oil recovery for reservoirs with low permeability. Even though CO2 could be miscible with oil in regions nearby injection wells, the miscibility could be lost in deep reservoirs because of low pressure and [...] Read more.
CO2 flooding is an important method for improving oil recovery for reservoirs with low permeability. Even though CO2 could be miscible with oil in regions nearby injection wells, the miscibility could be lost in deep reservoirs because of low pressure and the dispersion effect. Reducing the CO2–oil miscibility pressure can enlarge the miscible zone, particularly when the reservoir pressure is less than the needed minimum miscible pressure (MMP). Furthermore, adding intermediate hydrocarbons in the CO2–oil system can also lower the interfacial tension (IFT). In this study, we used dead crude oil from the H Block in the X oilfield to study the IFT and the MMP changes with different hydrocarbon agents. The hydrocarbon agents, including alkanes, alcohols, oil-soluble surfactants, and petroleum ethers, were mixed with the crude oil samples from the H Block, and their performances on reducing CO2–oil IFT and CO2–oil MMP were determined. Experimental results show that the CO2–oil MMP could be reduced by 6.19 MPa or 12.17% with petroleum ether in the boiling range of 30–60 °C. The effects of mass concentration of hydrocarbon agents on CO2–oil IFT and crude oil viscosity indicate that the petroleum ether in the boiling range of 30–60 °C with a mass concentration of 0.5% would be the best hydrocarbon agent for implementing CO2 miscible flooding in the H Block. Full article
(This article belongs to the Special Issue CO2 EOR and CO2 Storage in Oil Reservoirs)
Figures

Figure 1

Open AccessArticle
Use of Waste Glass as A Replacement for Raw Materials in Mortars with a Lower Environmental Impact
Energies 2019, 12(10), 1974; https://doi.org/10.3390/en12101974 (registering DOI)
Received: 14 April 2019 / Revised: 14 May 2019 / Accepted: 17 May 2019 / Published: 23 May 2019
PDF Full-text (3348 KB) | HTML Full-text | XML Full-text
Abstract
Glass waste used in mortars or concretes behaves similar to cement, with resulting environmental benefits. In this light, the behavior of glass powder of various particle sizes has been analyzed as a cement replacement in mortars, in an attempt to minimize the loss [...] Read more.
Glass waste used in mortars or concretes behaves similar to cement, with resulting environmental benefits. In this light, the behavior of glass powder of various particle sizes has been analyzed as a cement replacement in mortars, in an attempt to minimize the loss of strength and durability, and maximize the amount of materials replaced. The dry density, water accessible porosity, water absorption by immersion, capillary absorption coefficient, ultrasonic pulse velocity and both compressive and flexural strengths were studied in the mortars. Furthermore, a statistical analysis of the obtained results and a greenhouse gases assessment were also performed. In view of the results obtained, glass powder of 38 microns allows up to 30% of the cement to be replaced, due to the filler effect combined with its pozzolanic activity. Moreover, it has been observed that glass powder size is one of the factors with the greatest influence among the properties of porosity, absorption and capillarity. On the other hand, in the mechanical properties, this factor does not contribute significantly more than the amount of glass powder. Finally, the greenhouse gasses analysis shows that the incorporation of glass powder reduces the CO2 emissions associated with mortar up to 29.47%. Full article
Figures

Figure 1

Open AccessArticle
A Data-Driven Workflow Approach to Optimization of Fracture Spacing in Multi-Fractured Shale Oil Wells
Energies 2019, 12(10), 1973; https://doi.org/10.3390/en12101973 (registering DOI)
Received: 2 April 2019 / Revised: 17 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
PDF Full-text (3616 KB) | HTML Full-text | XML Full-text
Abstract
A data-driven workflow approach is presented in this study for optimizing fracture spacing of multifractured horizontal wells (MFHW) in shale oil reservoirs. The workflow employs a simple well productivity model for the initial design of hydraulic fracturing well completions. This provides a transparent [...] Read more.
A data-driven workflow approach is presented in this study for optimizing fracture spacing of multifractured horizontal wells (MFHW) in shale oil reservoirs. The workflow employs a simple well productivity model for the initial design of hydraulic fracturing well completions. This provides a transparent approach to the identification of key fracturing parameters affecting well productivity. The workflow uses transient pressure or production data to identify fracture interference. This offers a reliable and cost-effective means for assessment of well production potential in terms of optimization of fracture spacing in the MFHW. Result of a field case study indicated that three wells were drilled in an area with dense natural fractures, and the fracture spacing of MFHW in this area was short enough to effectively drain the stimulated reservoir volume (SRV), while the other three wells were drilled in an area with less natural fractures, and the fracture spacing of MFHW in this area could be shortened to double well productivity. Full article
(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)
Figures

Figure 1

Open AccessArticle
Investigation on Optimization Design of Offshore Wind Turbine Blades based on Particle Swarm Optimization
Energies 2019, 12(10), 1972; https://doi.org/10.3390/en12101972 (registering DOI)
Received: 30 April 2019 / Revised: 17 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
PDF Full-text (7494 KB) | HTML Full-text | XML Full-text
Abstract
Offshore wind power has become an important trend in global renewable energy development. Based on a particle swarm optimization (PSO) algorithm and FAST program, a time-domain coupled calculation model for a floating wind turbine is established, and a combined optimization design method for [...] Read more.
Offshore wind power has become an important trend in global renewable energy development. Based on a particle swarm optimization (PSO) algorithm and FAST program, a time-domain coupled calculation model for a floating wind turbine is established, and a combined optimization design method for the wind turbine’s blade is developed in this paper. The influence of waves on the power of the floating wind turbine is studied in this paper. The results show that, with the increase of wave height, the power fluctuation of the wind turbine increases and the average power of the wind turbine decreases. With the increase of wave period, the power oscillation amplitude of the wind turbine increases, and the power of the wind turbine at equilibrium position decreases. The optimal design of the offshore floating wind turbine blade under different wind speeds is carried out. The results show that the optimum effect of the blades is more obvious at low and mid-low wind speeds than at rated wind speeds. Considering the actual wind direction distribution in the sea area, the maximum power of the wind turbine can be increased by 3.8% after weighted optimization, and the chord length and the twist angle of the blade are reduced. Full article
(This article belongs to the Special Issue Wind Turbine Power Optimization Technology)
Figures

Figure 1

Open AccessArticle
A Generic Control-Oriented Model Order Reduction Approach for High Step-Up DC/DC Converters Based on Voltage Multiplier
Energies 2019, 12(10), 1971; https://doi.org/10.3390/en12101971 (registering DOI)
Received: 10 April 2019 / Revised: 15 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (8507 KB) | HTML Full-text | XML Full-text
Abstract
The modeling and control system design of high step-up DC/DC converters based on voltage multipliers (VMs) are difficult, due to the various circuit topologies and the presence of large number of capacitors in VMs. This paper proposes a generic approach to reduce the [...] Read more.
The modeling and control system design of high step-up DC/DC converters based on voltage multipliers (VMs) are difficult, due to the various circuit topologies and the presence of large number of capacitors in VMs. This paper proposes a generic approach to reduce the model order of such converters by replacing the VM capacitors with voltage sources controlled by the output voltage of the converter. Theoretical analysis and simulation results show that the derived models can accurately represent the low frequency response of the converter which is valuable for obtaining a small-signal AC model for control system design. The detailed modeling and controller design process are demonstrated for the converter, and the obtained simulation results are verified experimentally on a 400 W prototype. Full article
(This article belongs to the Special Issue Control in Power Electronics)
Figures

Figure 1

Open AccessArticle
Experimental and Numerical Characterization of the Sliding Rotary Vane Expander Intake Pressure in Order to Develop a Novel Control-Diagnostic Procedure
Energies 2019, 12(10), 1970; https://doi.org/10.3390/en12101970 (registering DOI)
Received: 6 May 2019 / Revised: 17 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (1699 KB) | HTML Full-text | XML Full-text
Abstract
Waste heat recovery via Organic Rankine Cycle (ORC)-based power units represents one of the most promising solutions to counteract the effects of CO2 emissions on climate change. Nevertheless, several aspects are still limiting its development on the on-the-road transportation sector. Among these [...] Read more.
Waste heat recovery via Organic Rankine Cycle (ORC)-based power units represents one of the most promising solutions to counteract the effects of CO2 emissions on climate change. Nevertheless, several aspects are still limiting its development on the on-the-road transportation sector. Among these aspects, the significant variations of the conditions of the hot source (exhaust gases) are a crucial point. Therefore, the components of the ORC-based unit operate far from the design point if the main operating parameters of the plant are not suitably controlled. The maximum pressure of the cycle is one of the most important variables to be controlled for the importance it has on the effectiveness of the recovery and on safety of operation. In this paper, a wide experimental and theoretical activity was performed in order to define the operating parameters that mostly affect the maximum pressure of the recovery unit. The results showed that the mass flow rate provided by the pump and the expander volumetric efficiency were the main drivers that affect the plant maximum pressure. Subsequently, through a validated model of the expander, a diagnostic map was outlined to evaluate if the expander and, consequently, the whole plant were properly working. Full article
(This article belongs to the Section Thermal Management)
Figures

Figure 1

Open AccessArticle
Techno-Economic Analysis of Hybrid Binary Cycles with Geothermal Energy and Biogas Waste Heat Recovery
Energies 2019, 12(10), 1969; https://doi.org/10.3390/en12101969 (registering DOI)
Received: 24 April 2019 / Revised: 12 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (2143 KB) | HTML Full-text | XML Full-text
Abstract
In Germany, enhancing renewable power generation represents a leading step to comply with the requirements of the Energiewende agenda. The geothermal reservoir in Oberhaching is assumed as a case study, with a gross electric power equal to 4.3 MWel. The intent [...] Read more.
In Germany, enhancing renewable power generation represents a leading step to comply with the requirements of the Energiewende agenda. The geothermal reservoir in Oberhaching is assumed as a case study, with a gross electric power equal to 4.3 MWel. The intent of this work is to design a hybrid binary geothermal power plant and to integrate it into the German energy market. Biogas waste thermal power equal to 1350 kWth is assumed as a secondary source. Two different layouts are defined for the hybrid solution: increasing the geothermal fluid temperature before entering the organic Rankine cycle (ORC) unit and superheating the working fluid after the evaporator. Stationary and quasi-stationary simulations have been performed with Aspen Plus V8.8. Results demonstrate how hybridization allows a maximum electric power increase of about 240 kWel. Off-design conditions are investigated regarding both the switch-off of exhaust gases and the annual ambient temperature fluctuations. In spite of the additional secondary source, the selected case studies cannot comply with the Minute reserve requirements (MRL). Moreover, economic results for both power-only and combined heat and power (CHP) configuration are provided. In the power-only configuration, the new-build hybrid system provides 15.42 €ct/kWh as levelized cost of electricity (LCOE), slightly lower than 16.4 €ct/kWh, as calculated in the geothermal-only solution. A CHP hybrid configuration shows a +19.22% increase in net cash flow at the end of the investment on the CHP geothermal solution. Full article
(This article belongs to the Special Issue Selected Papers from Heat Power Cycles Conference 2018)
Figures

Graphical abstract

Open AccessArticle
Improvement of Microbial Electrolysis Cell Activity by Using Anode Based on Combined Plasma-Pretreated Carbon Cloth and Stainless Steel
Energies 2019, 12(10), 1968; https://doi.org/10.3390/en12101968 (registering DOI)
Received: 14 April 2019 / Revised: 12 May 2019 / Accepted: 20 May 2019 / Published: 23 May 2019
PDF Full-text (3832 KB) | HTML Full-text | XML Full-text
Abstract
The anode activity in a microbial electrolysis cell (MEC) is known to be a limiting factor in hydrogen production. In this study, the MEC was constructed using different anode materials and a platinum-coated carbon-cloth cathode (CC). The anodes were comprised of CC, stainless [...] Read more.
The anode activity in a microbial electrolysis cell (MEC) is known to be a limiting factor in hydrogen production. In this study, the MEC was constructed using different anode materials and a platinum-coated carbon-cloth cathode (CC). The anodes were comprised of CC, stainless steel (SS), and a combination of the two (COMB). The CC and SS anodes were also treated with plasma to improve their surface morphology and hydrophilic properties (CCP and SSP, respectively). A combined version of CCP attached to SS was also applied (COMBP). After construction of the MEC using the different anodes, we conducted electrochemical measurements and examination of biofilm viability. Under an applied voltage of 0.6 V (Ag/AgCl), the currents of a MEC based on CCP and COMBP were 11.66 ± 0.1331 and 16.36 ± 0.3172 A m−2, respectively, which are about three times higher compared to the untreated CC and COMB. A MEC utilizing an untreated SS anode exhibited current of only 0.3712 ± 0.0108 A m−2. The highest biofilm viability of 0.92 OD540 ± 0.07 and hydrogen production rate of 0.0736 ± 0.0022 m3 d−1 m−2 at 0.8 V were obtained in MECs based on the COMBP anode. To our knowledge, this is the first study that evaluated the effect of plasma-treated anodes and the use of a combined anode composed of SS and CC for hydrogen evolution in a MEC. Full article
(This article belongs to the Section Bio-Energy)
Figures

Figure 1

Open AccessArticle
Assessment of Different Cooling Techniques for Reduced Mechanical Stress in the Windings of Electrical Machines
Energies 2019, 12(10), 1967; https://doi.org/10.3390/en12101967 (registering DOI)
Received: 23 April 2019 / Revised: 15 May 2019 / Accepted: 18 May 2019 / Published: 23 May 2019
PDF Full-text (9348 KB) | HTML Full-text | XML Full-text
Abstract
Thermal loading can induce mechanical stresses in the windings of electrical machines, especially those impregnated with epoxy resins, which is mostly the case in modern traction motors. Although designers look for cooling techniques that give better performance in terms of the power density [...] Read more.
Thermal loading can induce mechanical stresses in the windings of electrical machines, especially those impregnated with epoxy resins, which is mostly the case in modern traction motors. Although designers look for cooling techniques that give better performance in terms of the power density and efficiency of the machine, several thermal cycles can lead to fatigue and the degradation of the copper insulation, epoxy and consequently the windings. In this paper, the performance of different cooling techniques has been compared based on the temperature distribution and the mechanical stress induced in the windings. Three-dimensional finite element thermo-mechanical models were built to perform the study. Two different variants of water jacket cooling, two configurations of direct coil cooling and two cases of combined water jacket and direct coil cooling methods have been considered in the paper. The results show that the combined water jacket and direct coil cooling perform the best in terms of the temperature and also the mechanical stress induced in the windings. An experimental set-up is built and tested to validate the numerical results. Full article
Figures

Figure 1

Open AccessArticle
A Design of PWM Controlled Calibrator of Non-Sinusoidal Voltage Waveforms
Energies 2019, 12(10), 1966; https://doi.org/10.3390/en12101966 (registering DOI)
Received: 20 April 2019 / Revised: 16 May 2019 / Accepted: 21 May 2019 / Published: 23 May 2019
Viewed by 31 | PDF Full-text (4854 KB) | HTML Full-text | XML Full-text
Abstract
Power quality conditions in electrical power networks have drastically changed in recent years. A number of electrical devices and power generators that are the main sources of disturbances is ever increasing. Thus, the need for calibrators of different electrical equipment that will be [...] Read more.
Power quality conditions in electrical power networks have drastically changed in recent years. A number of electrical devices and power generators that are the main sources of disturbances is ever increasing. Thus, the need for calibrators of different electrical equipment that will be able to generate non-sinusoidal voltages and/or currents has proportionally increased. This paper presents a simple, unconventional approach of generating voltage harmonics, which do not rely on digital-to-analog (D/A) boards and power amplifier to amplify low-voltage signals. A fundamental part of the calibrator is the insulated gate bipolar transistor (IGBT) inverter with low-pass LRC filter at its output, which eliminates higher harmonics from the generated voltage. Desired voltage waveform is directly generated at the inverter’s output, thus the power amplifier is omitted from the setup. The modulation technique used for controlling IGBTs is the well-known sine pulse width modulation (PWM). Magnitudes and phase angles of the desired harmonics are regulated to compensate for the phenomena that may have a negative influence on their values: Nonlinearities of the system, temperature variation, voltage drops on parasitic components, etc. Experimental results show great potential of the proposed method for the design of the voltage calibrator for various electrical instruments. Full article
Figures

Figure 1

Open AccessArticle
Non-Probabilistic Time-Varying Reliability-Based Analysis of Corroded Pipelines Considering the Interaction of Multiple Uncertainty Variables
Energies 2019, 12(10), 1965; https://doi.org/10.3390/en12101965
Received: 9 April 2019 / Revised: 13 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
Viewed by 137 | PDF Full-text (882 KB)
Abstract
Reliability analysis of corroded pipelines is critical to the integrity and safe working of pipeline infrastructure. Aiming at less probability information is obtained for corrosion pipeline engineering, and the mechanical properties of pipeline with corrosion defects deteriorate caused by the accumulative effect of [...] Read more.
Reliability analysis of corroded pipelines is critical to the integrity and safe working of pipeline infrastructure. Aiming at less probability information is obtained for corrosion pipeline engineering, and the mechanical properties of pipeline with corrosion defects deteriorate caused by the accumulative effect of corrosion growth. Based on the quasi-static analysis method and non-probability theory, this paper presents a reliability model for assessing corroded pipelines with corrosion growth. In fact, reliability analysis of corroded pipelines needs to consider the interaction of multiple uncertainty variables. By introducing interaction theory, a mathematical model of corrosion defects considering the interaction of variables is put forward. Moreover, this paper develops a non-probabilistic time-varying reliability method for pipeline systems with multiple defects. Thus, several numerical examples are investigated to discuss the effectiveness of the proposed methodology. The results show that a two-dimensional or even three-dimensional ellipsoid model with correlation has more accurate results to evaluate corroded pipelines under the interaction of multiple corroded defects with poor information. Furthermore, a non-probabilistic time-varying reliability model is established according to the time-varying characteristics of the corroded pipeline under the influence of multiple factors. An effective complement to the theory of non-probabilistic reliability analysis of system is investigated. The analysis of the results suggests that interaction of corroded pipeline has a negligible impact on reliability. It also provides a theoretical basis for maintenance and is of great significance for risk- and reliability-informed decisions regarding buried oil and gas pipelines. Full article
Open AccessArticle
Experimental Investigation of Diesel Engine Performance, Combustion and Emissions Using a Novel Series of Dioctyl Phthalate (DOP) Biofuels Derived from Microalgae
Energies 2019, 12(10), 1964; https://doi.org/10.3390/en12101964
Received: 16 April 2019 / Revised: 16 May 2019 / Accepted: 17 May 2019 / Published: 22 May 2019
Viewed by 124 | PDF Full-text (4799 KB) | HTML Full-text | XML Full-text
Abstract
Physico-chemical properties of microalgae biodiesel depend on the microalgae species and oil extraction method. Dioctyl phthalate (DOP) is a clear, colourless and viscous liquid as a plasticizer. It is used in the processing of polyvinyl chloride (PVC) resin and polymers. A new potential [...] Read more.
Physico-chemical properties of microalgae biodiesel depend on the microalgae species and oil extraction method. Dioctyl phthalate (DOP) is a clear, colourless and viscous liquid as a plasticizer. It is used in the processing of polyvinyl chloride (PVC) resin and polymers. A new potential biofuel, hydrothermally liquefied microalgae bio-oil can contain nearly 11% (by mass) of DOP. This study investigated the feasibility of using up to 20% DOP blended in 80% diesel fuel (v/v) in an existing diesel engine, and assessed the performance and exhaust emissions. Despite reasonable differences in density, viscosity, surface tension, and boiling point, blends of DOP and diesel fuel were found to be entirely miscible and no separation was observed at any stage during prolonged miscibility tests. The engine test study found a slight decrease in peak cylinder pressure, brake, and indicated mean effective pressure, indicated power, brake power, and indicated and brake thermal efficiency with DOP blended fuels, where the specific fuel consumption increased. This is due to the presence of 16.4% oxygen in neat DOP, responsible for the relatively lower heating value, compared to that of diesel. The emission tests revealed a slight increase in nitrogen oxides (NOx) and carbon monoxide (CO) emissions from DOP blended fuels. However, particulate matter (PM) emissions were lower from DOP blended fuels, although some inconsistency in particle number (PN) was present among different engine loads. Full article
(This article belongs to the Section Energy and Environment)
Figures

Figure 1

Open AccessArticle
The Viscosity and Combustion Characteristics of Single-Droplet Water-Diesel Emulsion
Energies 2019, 12(10), 1963; https://doi.org/10.3390/en12101963
Received: 13 February 2019 / Revised: 31 March 2019 / Accepted: 10 May 2019 / Published: 22 May 2019
Viewed by 107 | PDF Full-text (3240 KB) | HTML Full-text | XML Full-text
Abstract
Diesel fuel exhibits excellent combustion characteristics and stability. However, diesel use is becoming restricted because of its associated environmental problems. Fuel emulsification, which increases efficiency and reduces pollution, became the solution of environmental problem. In this study, five water:diesel emulsions with mass ratios [...] Read more.
Diesel fuel exhibits excellent combustion characteristics and stability. However, diesel use is becoming restricted because of its associated environmental problems. Fuel emulsification, which increases efficiency and reduces pollution, became the solution of environmental problem. In this study, five water:diesel emulsions with mass ratios (0.3, 0.6, 1.0, 1.2, and 1.5) via ultrasonication were synthesized with and without surfactant. The optimal water:diesel ratio (=1:1) of an emulsion containing the surfactant was found by analyzing fuel concentration, mixing time, and viscosity. The combustion characteristics of single-droplet optimal emulsions were studied through ignition delay, burning rate, and total droplet lifetime at high temperature (400–700 °C) and pressure (1–15 bar), and micro-explosion phenomenon was observed. Although the ignition delay of emulsion increased, the total lifetime of the emulsion droplet was lower than that of diesel under 5 bar, 600 °C condition. Full article
Figures

Figure 1

Open AccessArticle
Assessment of Primary Energy Conversion of a Closed-Circuit OWC Wave Energy Converter
Energies 2019, 12(10), 1962; https://doi.org/10.3390/en12101962
Received: 12 March 2019 / Revised: 13 May 2019 / Accepted: 14 May 2019 / Published: 22 May 2019
Viewed by 102 | PDF Full-text (2584 KB) | HTML Full-text | XML Full-text
Abstract
Tupperwave is a wave energy device based on the Oscillating-Water-Column (OWC) concept. Unlike a conventional OWC, which creates a bidirectional air flow across the self-rectifying turbine, the Tupperwave device uses rectifying valves to create a smooth unidirectional air flow, which is harnessed by [...] Read more.
Tupperwave is a wave energy device based on the Oscillating-Water-Column (OWC) concept. Unlike a conventional OWC, which creates a bidirectional air flow across the self-rectifying turbine, the Tupperwave device uses rectifying valves to create a smooth unidirectional air flow, which is harnessed by a unidirectional turbine. This paper deals with the development and validation of time-domain numerical models from wave to pneumatic power for the Tupperwave device and the conventional OWC device using the same floating spar buoy structure. The numerical models are built using coupled hydrodynamic and thermodynamic equations. The isentropic assumption is used to describe the thermodynamic processes. A tank testing campaign of the two devices at 1/24th scale is described, and the results are used to validate the numerical models. The capacity of the innovative Tupperwave OWC concept to convert wave energy into useful pneumatic energy to the turbine is assessed and compared to the corresponding conventional OWC. Full article
Figures

Figure 1

Open AccessArticle
A Proportional Plus a Hysteretic Term Control Design: A Throttle Experimental Emulation to Wind Turbines Pitch Control
Energies 2019, 12(10), 1961; https://doi.org/10.3390/en12101961
Received: 4 May 2019 / Revised: 17 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
Viewed by 103 | PDF Full-text (2433 KB) | HTML Full-text | XML Full-text
Abstract
Pitch control is a relevant issue in wind turbines to properly operate the angle of the blades. Therefore, this control system pitches the blades usually a few degrees every time the wind changes in order to keep the rotor blades at the required [...] Read more.
Pitch control is a relevant issue in wind turbines to properly operate the angle of the blades. Therefore, this control system pitches the blades usually a few degrees every time the wind changes in order to keep the rotor blades at the required angle thus controlling the rotational speed of the turbine. All the same time, the control of the pitch angle is not easy due to the system behavior being highly nonlinear. Consequently, the main objective of this paper is to depict an easy to implement control design based on a proportional controller and a hysteretic term to an emulator pitch control system in wind turbines. This emulator is just an automotive throttle device. This mechanical body dynamically captures some hard non-linearities presented in pitch wind turbine mechanisms, such as backlash, asymmetrical non-lineal effects, friction, and load variations. Even under strong non-linear effects that are difficult to model, a proportional controller and a hysteretic term may satisfy the main control design objective. Hence, a recent control design is developed and applied to a throttle system. We invoke the Lyapunov theory to confirm stability of the resultant closed-loop system. In addition, the proposed control approach is completely implemented by using operational amplifiers. Hence, no digital units are required at all. Moreover, the cost of the developed experimental platform and its outcomes are inexpensive. According to the experimental results, the controller performance seems acceptable, and validating of the control contribution too. For instance, a settling-time of about 0.03 s to a unit step-response is obtained. Full article
Figures

Graphical abstract

Open AccessArticle
Biogas Production and Heat Transfer Performance of a Multiphase Flow Digester
Energies 2019, 12(10), 1960; https://doi.org/10.3390/en12101960
Received: 6 May 2019 / Revised: 19 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
Viewed by 95 | PDF Full-text (3566 KB) | HTML Full-text | XML Full-text
Abstract
Traditional static anaerobic digestion technology presents the disadvantages of a low gas production rate and long digestion cycle, which is not conducive to the treatment of livestock manure. A 12 m3 multiphase flow anaerobic digester (MFD) was developed in this study to [...] Read more.
Traditional static anaerobic digestion technology presents the disadvantages of a low gas production rate and long digestion cycle, which is not conducive to the treatment of livestock manure. A 12 m3 multiphase flow anaerobic digester (MFD) was developed in this study to improve the biogas production rate and maintain constant temperature digestion during winters. Full-scale field experiments were conducted on the biogas production rate at different temperatures, the dynamic digestion effects, and the dynamic heating digestion effects of the system at Sichuan, China. A comparison of the dynamic and static digestion results of 50 days indicated that the biogas production for the dynamic digestion (DD) group was 115.22 m3 or 127.1% higher than that of the static digestion (SD) group with the same digestion temperature. The results of the heat transfer performance experiment revealed that the heat transfer rate of the system increased significantly, and the temperature of the biogas slurry increased rapidly. The optimization analysis of the system was based on the experimental results of the relationship between the slurry temperature and biogas production rate, and the economical digestion temperature of the system was proposed and calculated. Different insulation materials or insulation thicknesses have an influence on the economical digestion temperature. Additionally, the economical digestion temperature of the system in which the polystyrene insulation layer with a thickness of 90 mm was used, was found to be 27.2 °C. When digestion temperature was 22.3 °C, the energy efficiency ratio (EER) of dynamic anaerobic digestion system is 1. The advantages of MFD are low biogas production unit cost and high heat and mass transfer rate. However, the disadvantage of high operation energy consumption needs further improvement. And additional energy was required when system digestion temperature below 22.3 °C. The proposed MFD and dynamic anaerobic digestion system can play a significant role in using biomass resources and promoting the development of biogas projects. Full article
(This article belongs to the Section Bio-Energy)
Figures

Figure 1

Open AccessArticle
Acoustic Emission Multi-Parameter Analysis of Dry and Saturated Sandstone with Cracks under Uniaxial Compression
Energies 2019, 12(10), 1959; https://doi.org/10.3390/en12101959
Received: 19 April 2019 / Revised: 13 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
Viewed by 91 | PDF Full-text (8844 KB) | HTML Full-text | XML Full-text
Abstract
In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation [...] Read more.
In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier; the cracks grow slowly; the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure; more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy. Full article
Figures

Figure 1

Open AccessArticle
Low-Carbon Futures for Bioethylene in the United States
Energies 2019, 12(10), 1958; https://doi.org/10.3390/en12101958
Received: 4 March 2019 / Revised: 17 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
Viewed by 97 | PDF Full-text (1775 KB) | HTML Full-text | XML Full-text
Abstract
The manufacture of the chemical ethylene, a key ingredient in plastics, currently depends on fossil-fuel-derived carbon and generates significant greenhouse gas emissions. Substituting ethylene’s fossil fuel feedstock with alternatives is important for addressing the challenge of global climate change. This paper compares four [...] Read more.
The manufacture of the chemical ethylene, a key ingredient in plastics, currently depends on fossil-fuel-derived carbon and generates significant greenhouse gas emissions. Substituting ethylene’s fossil fuel feedstock with alternatives is important for addressing the challenge of global climate change. This paper compares four scenarios for meeting future ethylene supply under differing societal approaches to climate change based on the Shared Socioeconomic Pathways. The four scenarios use four perspectives: (1) a sustainability-focused pathway that demands a swift transition to a bioeconomy within 30 years; (2) a regional energy-focused pathway that supports broad biomass use; (3) a fossil-fuel development pathway limited to corn grain; and (4) a fossil-fuel development pathway limited to corn grain and corn stover. Each scenario is developed using the latest scientifically informed future feedstock analyses from the 2016 Billion-Ton report interpreted with perspectives on the future of biomass from recent literature. The intent of this research is to examine how social, economic, and ecological changes determining ethylene supply fit within biophysical boundaries. This new approach to the ethylene feedstocks conundrum finds that phasing out fossil fuels as the main source of U.S. ethylene is possible if current cellulosic ethanol production expands. Full article
Figures

Figure 1

Energies EISSN 1996-1073 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top