New doctoral dissertation

May 15, 2025

VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Assessment of circularity constraints in the European Union’s solar photovoltaics supply chain“ prepared by VILNIUS TECH, Tadas Radavičius. The dissertation was prepared in 2020–2025. Scientific Consultant – Prof. Dr Manuela Tvaronavičienė.

The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Management in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 10 a.m. on 15 May 2025.

The dissertation focuses on analysing circularity constraints within a supply chain. The supply chain in this dissertation is defined as a circular supply chain (CSC) that includes materials, components, and end-of-life management of products. The identified research gap is a missing method for organisations to constantly improve circularity in the supply chain. The dissertation aims to propose a circular supply chain theoretical framework model for the continuous improvement of circularity in the CSC. Furthermore, a tool consisting of the sequence of the procedure for identification and assessment of circularity constraints is proposed and applied in the EU photo-voltaics (PV) industry. The literature analysis in the first chapter resulted in a list of indicators to measure circularity and the proposition of a CSC theoretical framework. The second chapter proposes a tool for identifying and assessing circularity constraints. It also describes the methods used. The third part of the dissertation provides the results of the methods used. Dissertation tasks include (1) analysing CE principles in supply chains, (2) analysing theories and concepts related to CE in supply chains, (3) developing an indicator system to measure circularity in the supply chain, (4) proposing a circular supply chain theoretical framework model, (5) proposing and applying a tool for circularity constraint assessment and solution identification in the EU PV supply chain. The dissertation proposed a circular supply chain theoretical framework model that expands the theory of constraints, knowledge management, resource-based view and resource-dependency theories. The research findings reveal how CE-related knowledge, resources, and capabilities impact the EU PV supply chain’s circularity potential. The dissertation findings are a list of circularity constraints within the EU PV supply chain. The constraints range from a fragmented regulatory approach for end-of-life PV module management in each EU member state to industry difficulties in cooperating for circularity purposes. The top priority is the hesitant exchange of information. Where most photovoltaics industry components are produced outside the European Union, it is difficult to obtain information regarding materials content, recyclability, disassembly, testing history, etc. The hesitant exchange of information also affects the top four constraints: insufficient traceability of photovoltaic modules, poor logistics handling in the reverse supply chain and illegal end-of-life photovoltaic module exports to non-European countries. The recommendations of the dissertation results suggest synchronising the regulatory landscape across the EU member states, standardising end-of-life PV module operators’ data sharing for circularity purposes, and implementing a centralised database in the EU to manage all CSC data related to circularity.
 
Doctoral dissertation readers can search via VILNIUS TECH Virtual Library.

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New doctoral dissertation
New doctoral dissertation
VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Performance investigation of a hybrid car engine fuelled with gasoline and gaseous mixtures“ („Benziną ir dujų mišinius naudojančio hibridinio automobilio variklio efektyvumo tyrimas“) prepared at VILNIUS TECH by Tadas Vipartas. The dissertation was prepared in 2021–2026. Scientific consultant – Prof. Dr Alfredas Rimkus. The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Transport Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 9 a.m. on 12 June 2026. This dissertation investigates the use of alternative fuels (natural gas and hydrogen) to increase the efficiency of a spark-ignition engine. The impact of different fuels and engine control algorithms on the combustion process and on energy and ecological indicators was determined and evaluated by analysing the emerging technological constraints within the context of a power-split (series-parallel) hybrid powertrain. The dissertation presents a review of scientific literature, analysing the directions for internal combustion engine improvement, the properties of gaseous fuels and the challenges of their application, along with the operating principles of automotive hybrid powertrains. Bench tests were conducted to investigate the effect of late intake valve closing timing on an engine operating on natural gas, and the influence of hydrogen additives on the combustion process and knock control. The numerical analysis of the engine’s combustion process was performed using AVL BOOST™ software, while the energy and ecological indicators of the hybrid vehicle were evaluated through experimental research and numerical simulation in the AVL CRUISE™ software. The following main results were obtained in the dissertation: retarding the intake valve closing timing increased the brake thermal efficiency and NOx emissions while reducing carbon dioxide emissions when the engine operates on natural gas. It was determined that a hydrogen additive in the fuel improves the engine’s energy indicators, but increases nitrogen oxides emissions and the risk of engine knock. Engine knock is effectively managed by retarding the ignition advance angle. Numerical simulation results confirmed that these trends persist during the Worldwide Harmonized Light-duty Vehicles Test Cycle: the use of hydrogen reduces fuel consumption and carbon dioxide emissions, but increases nitrogen oxides emissions. The dissertation results revealed the potential of these technologies and strategies for their application. The obtained data can be applied in the development and selection of advanced engine control algorithms and in the formulation of technologically sound environmental standards. Nine scientific articles have been published on the topic of the dissertation: six in scientific journals indexed in the Clarivate Analytics Web of Science database with an impact factor, one in a scientific journal indexed in the Clarivate Analytics Web of Science database without an impact factor, one in conference proceedings indexed in the Clarivate Analytics Web of Science Conference Proceedings Citation Index, and one in peer-reviewed conference proceedings not indexed in international databases. The research results were presented at three scientific conferences in Lithuania and Poland. Doctoral dissertation readers can search via VILNIUS TECH Virtual Library.
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