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The majority of Medium Voltage (MV) and Low Voltage (LV) power systems are based on and operate using Alternating Current (AC) infrastructures. Yet, modern energy market needs, which promote more decentralized concepts with a high... more
The majority of Medium Voltage (MV) and Low Voltage (LV) power systems are based on and operate using Alternating Current (AC) infrastructures. Yet, modern energy market needs, which promote more decentralized concepts with a high Renewable Energy Sources (RES) penetration rate and storage integration, bring Direct Current (DC) to the forefront. In this sense, AC/DC hybrid smart microgrids constitute a newly-introduced research field with a variety of potential applications that combine the benefits of both AC and DC systems. The purpose of this chapter is to review the advantages and disadvantages of AC/DC hybrid grids and analyze potential applications that would benefit from such infrastructures. Also, the most significant efforts and requirements for the constitution of a solid regulatory framework for AC/DC hybrid grids are presented, to pave the way towards their wider adoption by the market.
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The majority of Medium Voltage (MV) and Low Voltage (LV) power systems are based on and operate using Alternating Current (AC) infrastructures. Yet, modern energy market needs, which promote more decentralized concepts with a high... more
The majority of Medium Voltage (MV) and Low Voltage (LV) power systems are based on and operate using Alternating Current (AC) infrastructures. Yet, modern energy market needs, which promote more decentralized concepts with a high Renewable Energy Sources (RES) penetration rate and storage integration, bring Direct Current (DC) to the forefront. In this sense, AC/DC hybrid smart microgrids constitute a newly-introduced research field with a variety of potential applications that combine the benefits of both AC and DC systems. The purpose of this chapter is to review the advantages and disadvantages of AC/DC hybrid grids and analyze potential applications that would benefit from such infrastructures. Also, the most significant efforts and requirements for the constitution of a solid regulatory framework for AC/DC hybrid grids are presented, to pave the way towards their wider adoption by the market.
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Σκοπός της παρούσας διδακτορικής διατριβής είναι η πραγματοποίηση εκτεταμένης πειραματικής και θεωρητικής διερεύνησης της επίδρασης της χρήσης υγρών βιοκαυσίμων στη λειτουργική συμπεριφορά και τις εκπομπές ρύπων κινητήρα Diesel. Τα υγρά... more
Σκοπός της παρούσας διδακτορικής διατριβής είναι η πραγματοποίηση εκτεταμένης πειραματικής και θεωρητικής διερεύνησης της επίδρασης της χρήσης υγρών βιοκαυσίμων στη λειτουργική συμπεριφορά και τις εκπομπές ρύπων κινητήρα Diesel. Τα υγρά βιοκαύσιμα, τα οποία αποτέλεσαν το αντικείμενο της πειραματικής και θεωρητικής έρευνας, είναι το βιοντίζελ, τα φυτικά έλαια και η βιοαιθανόλη. Η πειραματική διερεύνηση έλαβε χώρα στον πρότυπο, πειραματικό, τετράχρονο κινητήρα Diesel άμεσης έγχυσης Ricardo/Cussons ‘Hydra’, ο οποίος είναι εγκατεστημένος σε μια πλήρως αυτοματοποιημένη κλίνη δοκιμών στο Εργαστήριο ΜΕΚ. Η πειραματική διερεύνηση του βιοντίζελ και των φυτικών ελαίων διενεργήθηκε παράλληλα, λόγω των κοινών χαρακτηριστικών των δύο καυσίμων, και συνίσταται σε δύο σειρές πειραματικών μετρήσεων. Η πρώτη σειρά μετρήσεων αφορά τη χρήση μιας μεγάλης ποικιλίας βιοντίζελ ή φυτικών ελαίων διαφόρων προελεύσεων σε μίγματα 10/90 και 20/80 (κατ’ όγκο) με το συμβατικό καύσιμο ντίζελ, με τον κινητήρα να λει...
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In the present work, the contemporary exhaust gas treatment systems (EGTS) used for SOx, PM, and NOx emission mitigation from shipping are reviewed. Specifically, after-treatment technologies such as wet scrubbers with seawater and... more
In the present work, the contemporary exhaust gas treatment systems (EGTS) used for SOx, PM, and NOx emission mitigation from shipping are reviewed. Specifically, after-treatment technologies such as wet scrubbers with seawater and freshwater solution with NaOH, hybrid wet scrubbers, wet scrubbers integrated in exhaust gas recirculation (EGR) installations, dry scrubbers, inert gas wet scrubbers and selective catalytic reduction (SCR) systems are analyzed. The operational principles and the construction specifications, the performance characteristics and the investment and operation of the reviewed shipping EGTS are thoroughly elaborated. The SCR technology is comparatively evaluated with alternative techniques such as LNG, internal engine modifications (IEM), direct water injection (DWI) and humid air motor (HAM) to assess the individual NOx emission reduction potential of each technology. Detailed real data for the time several cargo vessels spent in shipyards for seawater scrubbe...
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The increase of distributed energy resources (DERs) in low voltage (LV) distribution networks requires the ability to perform an accurate power flow analysis (PFA) in unbalanced systems. The characteristics of a well performing power flow... more
The increase of distributed energy resources (DERs) in low voltage (LV) distribution networks requires the ability to perform an accurate power flow analysis (PFA) in unbalanced systems. The characteristics of a well performing power flow algorithm are the production of accurate results, robustness and quick convergence. The current study proposes an improvement to an already used backward-forward sweep (BFS) power flow algorithm for unbalanced three-phase distribution networks. The proposed power flow algorithm can be implemented in large systems producing accurate results in a small amount of time using as little computational resources as possible. In this version of the algorithm, the network is represented in a tree-like structure, instead of an incidence matrix, avoiding the use of redundant computations and the storing of unnecessary data. An implementation of the method was developed in Python programming language and tested for 3 IEEE feeder test cases (the 4 bus feeder, th...
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The district heating (DH) system of Greece, mainly supported from lignite fired stations, is facing lately significant challenges. Stricter emission limits, decreased efficiency due to old age and increased costs are major challenges of... more
The district heating (DH) system of Greece, mainly supported from lignite fired stations, is facing lately significant challenges. Stricter emission limits, decreased efficiency due to old age and increased costs are major challenges of the lignite sector and are expected to result in the decommissioning of several lignite-fired units in the coming years. As a result, managers of DH networks are currently investigating alternative scenarios for the substitution of thermal power that it is expected to be lost, through the integration of Renewable Energy Sources (RES) into the system. In this paper, the DH systems of Kozani and Ptolemaida are examined regarding possible introduction of RES. The first study examines district heating of Kozani and alternative future options for covering a part of city’s thermal load whereas the second study refers to a biomass CHP plant (ORC technology, 1MWe, 5MWth) to be powered from a biomass mixture (wood chips and straw).
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This paper presents a day ahead optimal dispatch method for smart grids including two-axis tracking photovoltaic (PV) panels, wind turbines (WT), a battery energy storage system (BESS) and electric vehicles (EV), which serve as additional... more
This paper presents a day ahead optimal dispatch method for smart grids including two-axis tracking photovoltaic (PV) panels, wind turbines (WT), a battery energy storage system (BESS) and electric vehicles (EV), which serve as additional storage systems in vehicle to grid (V2G) mode. The aim of the day ahead schedule is the minimization of fuel-based energy, imported from the main grid. The feasibility of the proposed method lies on the extensive communication network of the smart grids, including sensors and metering devices, that provide valuable information regarding the production of the distributed energy resources (DER), the energy consumption and the behavior of EV users. The day ahead optimal dispatch method is applied on a smart grid in order to showcase its effectiveness in terms of sustainability, full exploitation of DER production and ability of EVs to act as prosumers.
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Annually, approximately 3 billion tires are commercially transacted worldwide each year and an equivalent amount is disposed of by the end of their life. Despite the increase in the life of tires and the global economic and pandemic... more
Annually, approximately 3 billion tires are commercially transacted worldwide each year and an equivalent amount is disposed of by the end of their life. Despite the increase in the life of tires and the global economic and pandemic crisis, the number of discarded tires is going to rise further due to the increasing demand for vehicles worldwide (approximately 5 billion tires by the end of 2030). The obsolete methods of tire disposal, including landfill, burning, etc., are a responsible for environmental issues (harmful substances production, air and soil pollution) and for the transmission of various diseases. Nowadays, approximately 70% of the total tires at the end of their life (ELTs) is recovered. The largest percentage of the recovered ELTs is intended for energy production or recovery as a fuel in cement industries or can be used for the production of various materials. A significant amount (approximately 95%) of the discarded ELTs can be reused. The products from the process...
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Direct current (DC) microgrids (MG) constitute a research field that has gained great attention over the past few years, challenging the well-established dominance of their alternating current (AC) counterparts in Low Voltage (LV) (up to... more
Direct current (DC) microgrids (MG) constitute a research field that has gained great attention over the past few years, challenging the well-established dominance of their alternating current (AC) counterparts in Low Voltage (LV) (up to 1.5 kV) as well as Medium Voltage (MV) applications (up to 50 kV). The main reasons behind this change are: (i) the ascending amalgamation of Renewable Energy Sources (RES) and Battery Energy Storage Systems (BESS), which predominantly supply DC power to the energy mix that meets electrical power demand and (ii) the ascending use of electronic loads and other DC-powered devices by the end-users. In this sense, DC distribution provides a more efficient interface between the majority of Distributed Energy Resources (DER) and part of the total load of a MG. The early adopters of DC MGs include mostly buildings with high RES production, ships, data centers, electric vehicle (EV) charging stations and traction systems. However, the lack of expertise and ...
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Since the widespread deployment of non-dispatchable, intermittent, and highly variable power production from renewable energy sources (RES), the demand for flexible power production has been steadily growing. As new-built dispatchable... more
Since the widespread deployment of non-dispatchable, intermittent, and highly variable power production from renewable energy sources (RES), the demand for flexible power production has been steadily growing. As new-built dispatchable power plants have not been very quickly adapted to the emerging flexible operation, this task has been addressed by existing plants as well. Existing solid-fuel thermal power plants have undergone an extensive study to increase their flexible operation. Thermodynamic process-modeling tools have been extensively used for plant modeling. Steady- and transient-state simulations have been performed under various operating regimes, supplying valuable results for efficient power-plant operation. Flexibility aspects regarding low-load operation and steady operational conditions are mostly investigated with steady-state simulations. Flexibility aspects related to variation over time such as ramping rates are investigated with transient simulations. The off-des...
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This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using... more
This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations. The proposed methodology is useful for a wide spectrum of applications, in which no access to experimental data or conduction of several CFD runs is possible, deriving a simple expression of natural ventilation rate, which can be further used for energy analysis of complicated building geometries in 0-D models or in object-oriented software codes. The developed computational model simulates a building, which belongs to Rheinisch-Westfälische Technische Hochschule (RWTH, Aachen University, Aachen, Germany) and its surrounding environment. A tilted window represents the opening that allows the ventilation of the adjacent room with fresh air. The derived data from the CFD simulations for t...
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There is a growing interest over the last decades in the field of autonomous island grids that is driven mainly by climate reasons. The common objective among the members of the European Union (EU) is the increase of Renewable Energy... more
There is a growing interest over the last decades in the field of autonomous island grids that is driven mainly by climate reasons. The common objective among the members of the European Union (EU) is the increase of Renewable Energy Sources (RES) penetration in the energy mixture, as well as turning the grid into a smart grid. Consequently, more and more state-of-the-art solutions are being proposed for the electricity generation and the optimization of the energy system management, taking advantage of innovations in all energy related sectors. The evaluation of all available solutions requires quantitative assessment, through the adoption of representative Key Performance Indicators (KPIs) for the projects that are related to smart grid development in isolated energy systems, providing the relevant stakeholders with a useful comparison among the proposed solutions. The evaluation approach that is described in this paper emphasizes the role of the various stakeholder groups who fac...
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Cities are challenged with increasing population growth and need to implement smart solutions to become more resilient to economic, environmental, and social challenges posed by ongoing urbanization. This study reviewed business model... more
Cities are challenged with increasing population growth and need to implement smart solutions to become more resilient to economic, environmental, and social challenges posed by ongoing urbanization. This study reviewed business model development frameworks and developed a practical tool to help cities assess business models by adapting components of the Business Model Canvas (BMC) and adding new ones that operationalize the smart city dimensions. The Smart City BMC (SC-BMC) proposed provides a practical framework that supports developing and communicating a more holistic and integrated view of a smart city business model. It also supports creatively innovating toward more sustainable value creation. As a framework, the SC-BMC bridges sustainable value creation for business model development and smart city innovation.
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ABSTRACT This experimental investigation evaluates the combustion and exhaust emission characteristics of cottonseed oil and its (methyl ester) bio-diesel in blends with 20% by vol. of either n-butanol or diethyl ether (DEE), fueling a... more
ABSTRACT This experimental investigation evaluates the combustion and exhaust emission characteristics of cottonseed oil and its (methyl ester) bio-diesel in blends with 20% by vol. of either n-butanol or diethyl ether (DEE), fueling a standard, experimental, single-cylinder, four-stroke, high-speed direct injection (HSDI), ‘Hydra’ diesel engine. The tests are conducted using each of the above fuel blends or neat cottonseed oil or its neat bio-diesel, with the engine operating at three different loads. Fuel consumption, exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO) and total unburned hydrocarbons (HCs) are measured. The differences in the performance and exhaust emissions of these fuel blends from the baseline operation of the diesel engine, i.e. when working with neat cottonseed oil or its neat bio-diesel, are compared. Fuel injection and combustion chamber pressure diagrams are obtained, and heat release rate analysis of the latter ones is performed revealing some interesting features of the combustion mechanisms. These results and the widely differing physical and chemical properties of n-butanol and DEE against those for the cottonseed oil and its bio-diesel are used to aid the correct interpretation of the observed engine behavior. It is revealed that n-butanol and DEE, which can be produced from biomass (bio-butanol and bio-DEE), when added to the vegetable oil or its bio-diesel improve the behavior of diesel engine.
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... Mechanical Engineering, National Technical University of Athens, Athens 15780, Greece. Yiannis A. Levendis*. Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115. ... (26) Arkoudeas, P.;... more
... Mechanical Engineering, National Technical University of Athens, Athens 15780, Greece. Yiannis A. Levendis*. Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115. ... (26) Arkoudeas, P.; Kalligeros, S.; Zannikos, F.; Anastopoulos, G ...
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ABSTRACT An experimental study is conducted to evaluate the performance and exhaust emissions characteristics of diesel fuel blends with 8%, 16% and 24% (by vol.) diethyl ether (DEE), in a standard, experimental, single-cylinder,... more
ABSTRACT An experimental study is conducted to evaluate the performance and exhaust emissions characteristics of diesel fuel blends with 8%, 16% and 24% (by vol.) diethyl ether (DEE), in a standard, experimental, single-cylinder, four-stroke, high-speed direct injection (HSDI), ‘Hydra’ diesel engine located at the authors' laboratory. The tests are conducted using each of the fuel blends or neat diesel fuel, with the engine working at three different loads. Fuel consumption, exhaust smoke, and regulated gas emissions such as nitrogen oxides, carbon monoxide and unburned hydrocarbons are measured. The differences in the performance and exhaust emission parameters of the three DEE/diesel fuel blends from the baseline operation of the diesel engine, i.e., when working with neat diesel fuel, are compared. Combustion chamber and fuel injection pressure diagrams are obtained, and heat release rate analysis of the experimentally obtained cylinder pressure diagrams is performed, revealing some interesting features of the combustion mechanisms. These results and the widely differing physical and chemical properties of DEE against those for diesel fuel are used to aid the interpretation of the observed engine behavior. It is revealed that this fuel, which can be produced from biomass (bio-DEE), is a promising one for diesel engines.
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The modeling of turbocharged diesel engine transient operation appeared in the early 1970s and continues to be in the focal point of research due to the importance of transient response in the everyday operating conditions of engines.... more
The modeling of turbocharged diesel engine transient operation appeared in the early 1970s and continues to be in the focal point of research due to the importance of transient response in the everyday operating conditions of engines. Simulations of various levels of complexity have been used so far to study engine performance during transients. On the other hand, the very important issue of exhaust emissions has been studied mainly on an experimental rather than simulation basis, owing to the high computational time required for the analysis of many cycles. The study of transient emissions from turbocharged diesel engines is extremely important for the manufacturers, since newly produced engines must meet the stringent regulations concerning exhaust emissions levels. In the present work, a comprehensive two-zone transient diesel combustion model is used for a parametric analysis of exhaust emissions prediction during load changes. The parameters studied are the load characteristics...