Piras, Marco (2023) Advancing Sustainable Transportation: A Comprehensive Study on Alternative Fuels, Powertrain Technologies, and Energy Management Strategies. [Tesi di dottorato]

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Abstract

To mitigate the impacts of global warming, the effects of which are evident in our daily lives, major countries around the world are pushing for new and more stringent regulations that affect the transportation sector, responsible for a significant portion of CO2 emissions in the atmosphere. It is within this context that industries and researchers are pushing the boundaries of knowledge to discover technological solutions for the environmental and political challenges that arise periodically. This PhD thesis aims to introduce the reader to some of these solutions, demonstrating that the transportation sector can be transformed towards carbon neutrality through various approaches operating at different stages of decarbonization. Four main layers of decarbonization are identified. It is widely acknowledged that the most commonly used propulsion system for our vehicles today is the internal combustion engine (ICE), which is simultaneously identified as a major source of gaseous CO2. However, it is important to note that the source of pollutants lies in the fuel, rather than the engine itself. Therefore, the first step in achieving carbon neutrality involves addressing the nature of the fuel, which can either be burned in an ICE or chemically converted in fuel cells. Currently, biofuels and e-fuels, with a strong focus on hydrogen, are subjects of extensive research and testing. The second layer of decarbonization involves optimizing the propulsion system that converts the chemical energy from fuel (or stored in a battery) into mechanical power for propulsion. This PhD thesis primarily focuses on ICEs and fuel cells. Concerning ICE-powered vehicles, a critical challenge is managing the existing vehicle fleet until it reaches the end of its life while minimizing its environmental impact. In this context, it is crucial to enhance and convert existing ICEs. One potential technical solution is water injection. A numerical study conducted during this PhD work demonstrated the benefits of applying this strategy to a gasoline spark ignition engine, highlighting advantages in terms of both efficiency and performance with the implementation of an appropriate control strategy. Hydrogen-fueled engines are another important area of research. They have the potential to reduce CO2 tailpipe emissions from ICEs to nearly zero; however, they still present technological challenges. During this doctoral research, a phenomenological 1D model of a hydrogen fueled engine was developed and validated, showing satisfactory agreement with experimental data. Consequently, this model serves as a valuable tool for a comprehensive understanding of hydrogen engines. Fuel cell vehicles are progressively gaining a larger market share and can unquestionably serve as a practical alternative to ICE-powered vehicles. The fourth chapter provides a comprehensive overview of fuel cell systems, including a discussion of various widely adopted technologies. Following this, a detailed description of the fuel cell system model utilized in the development of a Fuel Cell Hybrid Electric Vehicle (FCHEV) model is presented. The third layer of decarbonization pertains to the vehicles themselves. Optimizing the powertrain is imperative, and hybrid vehicles have effectively demonstrated that by amalgamating various technologies (such as ICEs, batteries, fuel cells, supercapacitors, etc.), the full potential of each component can be unlocked. When these components operate in isolation, they may not achieve the same level of performance. However, the growing complexity of powertrains necessitates a suitable energy management system, which constitutes the fourth and final decarbonization layer investigated in this PhD study. After a concise review of the literature, this doctoral research introduces an expansion of the ETESS (Efficient Thermal-Electric Skipping Strategy). This expansion aims to enhance energy management in Plug-in Hybrid Electric Vehicles (PHEVs) equipped with small-sized engines. The core concept underlying this approach revolves around the alternative utilization of both the thermal engine and electric motor to fulfill the power requirements for propulsion. In recent years, the rapid advancements in artificial intelligence and computer technologies have led to the increasing adoption of learning algorithms within the field of Energy Management Strategies, positioning it as a burgeoning and highly esteemed research area. As a result, during the last part of this PhD work, an EMS enhanced by the incorporation of neural networks has been developed and tested for a heavy-duty FCHEV.

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