Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Exergy-Based Evaluation of High-CO2 Biogas/Diesel RCCI Combustion Heat Flow for Enhanced Mixture Distribution, Power Output, and Fuel-Energy Performance(Pergamon-Elsevier Science Ltd, 2026) Dalha, Ibrahim B.; El-Adawy, Mohammed; Wong, Nur Leena W. S.; Man, Hafsalina C.; Said, Mior A.; Koca, Kemal; Abdulsalam, MuhammedUtilising high-CO2 biogas in compression-ignition engines poses significant challenges due to poor mixture reactivity, inefficient combustion, and increased energy degradation. This work addresses these difficulties by conducting experimental research on a port-injection at the valve reactivity-controlled compression ignition (PIVE-RCCI) strategy. This study addresses these concerns by conducting experiments on a PIVE-RCCI technique to improve mixture distribution and combustion efficiency in biogas-diesel engines. The engine was modified to provide biogas through the inlet valve, allowing for controlled variations of biogas injection pressure (BIP: 1-4 bar) and port swirl ratio (PSR: 0-80%) at 1600 rpm and 4.9-5.7 bar IMEP. Energy and exergy analyses were used to determine the effect of intake flow dynamics on temperature uniformity, heat transfer, and power generation during combustion. The results reveal that normal airflow conditions minimise accounted heat loss, indicating higher thermal efficiency (ITE) and increased output power across all BIPs. In contrast, introducing a strong intake swirl dramatically improves combustion performance. The 80% PSR configuration resulted in the lowest exergy destruction and the maximum energy recovery potential, with an ITE of 26.54% at 4 bar BIP. Increasing BIP increased power output, whereas the optimal combustion work was found at 1 bar BIP and 40% PSR. The optimal working conditions were 1 bar BIP, 80% PSR, and 5.45 bar IMEP, which resulted in 26.00% exergy destruction, 39.38% destruction-to-released exergy ratio, 86.00% exergy-energy ratio of heat transfer, and 63.78% exhaust exergy-energy ratio. This work's novelty lies in integrating biogas injection, intake swirl control, and exergy-based evaluation to measure mixture distribution and energy recovery in high-COQ biogas RCCI combustion. The findings offer useful operational guidance for increasing energy efficiency and advancing the commercialization of renewable gaseous fuels in RCCI engines. As a result, operating the engine at half load, 80% PSR, and atmospheric air pressure (1 bar) conditions significantly enhanced the combustion efficiency and energy utilisation.Article Citation - WoS: 11Citation - Scopus: 13Wireless Sensor Network-Based Communication for Cooperative Simultaneous Localization and Mapping(Pergamon-Elsevier Science Ltd, 2015-01) Tuna, Gurkan; Gungor, Vehbi Cagri; Potirakis, Stelios M.; Zeadally, SheraliThis paper presents a novel approach of using a Wireless Sensor Network (WSN) as the communication means for Multi-Robot, Cooperative, Simultaneous Localization and Mapping (CSLAM) applications investigating the associated design challenges and suggesting corresponding solutions. Although the proposed approach brings several benefits including an increased coverage and communication range, self-organization capabilities, quick deployment, and flexible architecture, the realization is interrelated with performance in terms of energy efficiency and reliability. In this respect, the applicability of the WSNs for the presented approach is investigated. Centralized and distributed map merging methods in WSN-based CSLAM are evaluated in detail and the impacts of packet delays and losses on the performance of CSLAM algorithms are shown. Additionally, the involved network congestion and contention dynamics are presented, while the effects of observation range, speed, time intervals between observations, and odometry readings on the SLAM accuracy are shown based on an extensive set of simulation studies. (C) 2014 Elsevier Ltd. All rights reserved.Article Citation - WoS: 30Citation - Scopus: 31Three Dimensional Stress Analysis of Solid Oxide Fuel Cell Anode Micro Structure(Pergamon-Elsevier Science Ltd, 2014-11) Celik, Selahattin; Ibrahimoglu, Beycan; Toros, Serkan; Mat, Mahmut D.One of the most common problems in solid oxide fuel cells (SOFCs) is the delamination and thus the degradation of electrode/electrolyte interface which occurs in the consequences of the stresses generated within the different layers of the cell. Nowadays, the modeling of this problem under certain conditions is one of the main issues for the researchers. The structural and thermo-physical properties of the cell materials (i.e. porosity, density, Young's modulus etc.) are usually assumed to be homogenous in the mathematical modeling of solid oxide fuel cells at macro-scale. However, during the real operation, the stresses created in the multiphase porous layers might be very different than those at macro-scale. Therefore, micro-level modeling is required for an accurate estimation of the real stresses and the performance of SOFCs. This study presents a microstructural characterization and a finite element analysis of the delamination and the degradation of porous solid oxide fuel cell anode and electrode/electrolyte interface under various operating temperatures, compressing forces and material compositions by using the synthetically generated microstructures. A multi physics computational package (COMSOL) is employed to calculate the Von Misses stresses in the anode microstructures. The maximum thermal stress in the electrode/electrolyte interface and three phase boundaries is found to exceed the yield strength at 900 degrees C while 800 degrees C is estimated as a critical temperature for the delamination and micro cracks due to thermal stress generated. The thermal stress decreases in the grain boundaries with increasing content of one of the phases (either Ni or YSZ) and the porosity of the electrode. A clamping load higher than 5 kg cm(-2) is also found to exceed the shear stress limit. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 479Citation - Scopus: 548The Role of Renewable Versus Non-Renewable Energy to the Level of Co2 Emissions a Panel Analysis of Sub-Saharan Africa's Big 10 Electricity Generators(Pergamon-Elsevier Science Ltd, 2018-08) Inglesi-Lotz, Roula; Dogan, EyupUndoubtedly, the increasing rates of CO2 emissions contribute highly to climate change. Studies stress the importance of understanding the determinants of emissions, in order to implement appropriate policies. In the past, literature only looked at the effect of aggregate energy to emissions; while nowadays, with the increasing role of renewables, they aim at evaluating the impacts of renewable and nonrenewable energies separately. Also, studies ignored possible cross-dependence among countries; concept particularly important for countries linked by trade or geographical position. Also, only lately, studies focused on developing economies. In this study, we aim to address these gaps of the literature by estimating the determinants (renewable and non-renewable energy, income and trade openness) of CO2 emissions for the ten biggest electricity generators in Sub-Saharan Africa for the period 1980 to 2011 by employing panel estimation techniques robust to cross dependence. A long-run relationship between the main variables is confirmed. Increases in non-renewable energy consumption intensify pollution while the opposite holds for renewable energy. With regards to direction of causal relationships, we observe a unidirectional causality running from emissions, income, trade and non-renewable energies towards renewable energies; from nonrenewable energy to emissions; and from emissions and non-renewable energies to trade. (C) 2018 Elsevier Ltd. All rights reserved.Article Citation - WoS: 221Citation - Scopus: 240The Role of Interaction Effect Between Renewable Energy Consumption and Real Income in Carbon Emissions: Evidence From Low-Income Countries(Pergamon-Elsevier Science Ltd, 2022-02) Ehigiamusoe, Kizito Uyi; Dogan, EyupEven though the existing studies have extensively investigated the impacts of renewable energy and real income on carbon emissions, the literature overlooks the role of their interaction effect in the level of emissions. In addition, the studies have usually chosen high-income and middle-income countries as focused group. To fill these gaps in the existing body of energy-environment literature, this study investigates the impacts of real income, renewable energy consumption and their interaction effect on carbon emissions in low-income countries by employing empirical estimations that control different econometric and economic issues such as heterogeneity and cross-sectional dependence. The results reveal that renewable energy mitigates emissions; however, the interaction effect stays positive. The marginal effect of renewable energy on emissions varies with the levels of real income. Policymakers in these economies should implement policies and regulations to promote the adoption and use of renewable energy to mitigate carbon emissions. Besides, this study emphasizes that the levels of renewable energy and real income are not the only panacea to abating pollution, but the interaction effect should be considered in ensuring environmental sustainability.Article Citation - WoS: 40Citation - Scopus: 43The Role of Hydrogen in the Edge Dislocation Mobility and Grain Boundary-Dislocation Interaction in Α-Fe(Pergamon-Elsevier Science Ltd, 2021-09) Kapci, Mehmet Fazil; Schoen, J. Christian; Bal, Burak; Schön, J. ChristianThe atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of alpha-Fe, specifically 1/2<111>{110} and 1/2<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations -in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism-, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 204Citation - Scopus: 234The Relationship Between Economic Growth and Electricity Consumption From Renewable and Non-Renewable Sources: A Study of Turkey(Pergamon-Elsevier Science Ltd, 2015-12) Dogan, EyupThe main objective of this study is to analyze the short and long run estimates as well as the causality relationships between economic growth (GR), electricity consumption from renewable sources (RELC) and electricity consumption from non-renewable sources (NRELC) for Turkey in a multivariate model wherein capital (K) and labor (L) are included as additional variables. Using the autoregressive distributed lag (ARDL) approach to cointegration, the Johansen cointegration test and the Gregory-Hansen cointegration test with structural break, we show that GR, RELC, NRELC, K and L are cointegrated. Although NRELC has a long run positive effect on GR, the long run estimate of RELC is negative but insignificant at 5% level of significance. The Granger causality test based on the vector error correction model reveals the evidence of neutrality hypothesis between RELC and GR, and between NRELC and GR in Turkey in the short run. In addition, the Granger causality runs from RELC, NRELC, K and L to GR as well as from GR, RELC, K and L to NRELC in the long run, which supports the existence of growth hypothesis between RELC and GR, and feedback hypothesis between NRELC and GR in the long run. It is advised that policy makers in the Turkish government should continue to reduce the share of electricity consumption from renewable sources and encourage the usage of electricity from non-renewable sources to have sustainable long run growth rates. It is also essential to promote the investment projects to increase the efficiency of electricity generation from non-renewable sources. (C) 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 810Citation - Scopus: 926The Influence of Real Output, Renewable and Non-Renewable Energy, Trade and Financial Development on Carbon Emissions in the Top Renewable Energy Countries(Pergamon-Elsevier Science Ltd, 2016-07) Dogan, Eyup; Seker, FahriDue to tremendous increase in the level of carbon dioxide (CO2) emissions in the last several decades, a number of studies in the energy-growth-environment literature have attempted to identify the determinants of CO2 emissions. A major criticism related to the existing studies, we realize, is the selection of panel estimation techniques. Almost all studies use panel methods that ignore the issue of cross-sectional dependence even though countries in the panel are most likely heterogeneous and cross-sectionally dependent In addition, the majority of existing studies use aggregate energy consumption, and thus fail to identify the impacts of energy consumption by sources on the environment In order to fulfill the mentioned gaps in the literature, this empirical study analyzes the influence of the real income, renewable energy consumption, non-renewable energy consumption, trade openness and financial development on CO2 emissions in the EKC model for the top countries listed in the Renewable Energy Country Attractiveness Index by employing heterogeneous panel estimation techniques with cross-section dependence. We find that the analyzed variables become stationary at their first-differences by using the CADF and the CIPS unit root tests, and the analyzed variables are cointegrated by employing the LM bootstrap cointegration test By using the FMOLS and the DOLS, we also find that increases in renewable energy consumption, trade openness and financial development decrease carbon emissions while increases in non-renewable energy consumption contribute to the level of emissions, and the EKC hypothesis is supported for the top renewable energy countries. (C) 2016 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 9The Effect of Spoilers on Flow Around Tandem Circular Cylinders(Pergamon-Elsevier Science Ltd, 2023-03) Ilkentapar, Mucella; Aksit, Serhat; Acikel, Halil Hakan; Oner, Ahmet AlperExamining the flow characteristics around the cylindrical elements, such as offshore (submarine) pipelines which can be used in single or multiple arrangements, has a prominent place in fluid mechanics. The use of spoilers for self-embedding of these structures has been a subject that researchers have studied for many years. In this study, (a) the flow around a cylinder without and with a spoiler and (b) the effect of adding spoiler(s) to the tandem cylinders on the flow was experimentally investigated. In these experiments, where the ratio of the distance between the cylinders to the cylinder diameter is 2, the Reynolds number is 14000, which remains in the subcritical region. Four experiments were performed: the smoke-wire method was used for flow visualization, aerodynamic force measurement, velocity measurement by hot-wire anemometer, and pressure measurement to determine the pressure distribution on the cylinders. Pressure, velocity, and force results were recorded with the time histories in this study for the first time. Experimental studies show that when a spoiler is added to a single cylinder, an opposing lift force acts on that and the drag force increases due to the enlargement of the lowpressure region at the wake of the cylinder. In a tandem situation, when the upstream cylinder has a spoiler, no drag force acts on the downstream cylinder. The forces exerted on the upstream cylinder are not affected by whether the downstream cylinder has a spoiler. In the case of the downstream cylinder with the spoiler, the fluctuations in the aerodynamic forces of the upstream cylinder decrease owing to the downstream cylinder with the spoiler. The force fluctuations are more in the downstream cylinder, and unlike other tandem and singlecylinder cases, the vortex shedding becomes complex.Article Citation - WoS: 30Citation - Scopus: 37Testing of 17-Different Leaching Agents for the Recovery of Zinc From a Carbonate-Type Pb-Zn Ore Flotation Tailing(Pergamon-Elsevier Science Ltd, 2021-07) Hussaini, Shokrullah; Kursunoglu, Sait; Top, Soner; Ichlas, Zela Tanlega; Kaya, MuammerThe recovery of zinc from a flotation tailing using 17-different leaching agents, including inorganic and organic acids, alkaline solutions and chelating agents, was investigated. The effects of the lixiviant type, acid concentration, leaching temperature, leaching time, and solid-to-liquid ratio on the metals dissolution were studied. The use of sulfuric acid resulted in 91% of zinc extraction with a high selectivity against lead. The major impurities of lead, iron, calcium and arsenic precipitated during the leaching process as a segnisite, beudantite, gypsum, and goethite in this lixiviant. It was seen that the addition of oxidants in sulfuric acid solution slightly increased zinc dissolution. The citric acid dissolved 90.1% of zinc along with 9.1% lead. 90% of zinc dissolution was achieved by using malic acid, and high selectivity between zinc and lead dissolutions was also observed. The citric and malic acid leach residues contained a substantial amount of segnitite, beudantite, and quartz as the major phases. In term of zinc and lead dissolution selectivity, the best inorganic agents were determined in the following order: sulfuric acid > hydrochloric acid > perchloric acid > nitric acid. With organic agents, the best zinc and lead selectivity was achieved in the following order: sulfosalicylic acid > citric acid > malic acid > formic acid > tartaric acid > ascorbic acid. The best simultaneous zinc and lead dissolutions were achieved using sodium hydroxide agent. Using 5 M sodium hydroxide at 80 degrees C and 1/10 solid-to-liquid ratio for 180 min. leaching time, 81.4% of zinc and 47.4% of lead were dissolved while leaving a considerable amount of iron in the residue. When the ammonium chloride was used as a lixiviant, the silver and zinc were taken into the leach solution. 61.3% of zinc dissolution was obtained by using 50% ammonia as lixiviant, whereas no iron and lead dissolutions were observed. Using 0.37 M EDTA at 80 degrees C, 1/10 solid-to-liquid ratio for 180 min. leaching time, more than 90% of zinc dissolved along with a substantial amount of iron, arsenic and lead co-dissolutions. 47.4% of zinc dissolution was obtained at 80 degrees C and 1/10 solid-to-liquid ratio for 180 min. leaching time when sodium citrate was used as lixiviant, whereas less than 20% of zinc dissolved using ammonium oxalate at similar leaching condition. 39% zinc was dissolved using 3 M ammonium acetate at 80 degrees C, 1/10 solid-to-liquid ratio for 180 min., while 23.1% of zinc dissolution was achieved when the ammonium acetate was tested under similar experimental conditions. As a result, sulfuric, citric, malic, sulfosalicylic and formic acids were deemed to be the most promising leaching agents for the selective recovery of zinc from the lead-zinc flotation tailing.