Riassunto analitico
In recent years, the automotive sector has faced a deep change towards electrification. On the one hand, new technologically advanced battery electric vehicles (BEV) have made their appearance on the industrial market, while, on the other hand, traditional internal combustion engine vehicles (ICE vehicles) have undergone deep changes in their architecture. This is due to the possibility of coupling the internal combustion engine with electric motors in different configurations, which has enabled a considerable gain in the efficiency of powertrains, resulting in lower specific fuel consumption, and so, in lower greenhouse gas emissions. In particular, parallel hybrid and power split hybrid configurations are those most promising that have gained popularity in the last decade: indeed, for what concerns passenger cars, they represent a contribution to engine downsizing, together with the application of turbocharging technology, enabling the possibility to have “engine-on-demand”, operating in conditions near its maximum efficiency for most of the time. Moreover, parallel hybrid is also used in high-performance cars and in motorsports applications, because it enhances vehicle performances, thanks to the high-torque availability of electric motors at low speeds and to the possibility of recovering energy that would be lost otherwise, both mechanical (MGU-K recovery system) and thermal (MGU-H recovery system).
The aim of this thesis is to present a study concerning the application of an electrically actuated compressor on a high-performance internal combustion engine, exploiting the concept of e-boost. This technology eliminates problems of turbo-lag and enables the usage of compressors working also at relatively low engine speeds. This type of configuration is not new, some studies have been made in the past concerning the application of e-boost on downsized passenger cars; in this case, however, this technology is studied for a high-displacement ICE, originally naturally aspirated, whose performances in terms of torque availability need to be improved. Furthermore, to avoid adding complexity to the exhaust line, the turbine is not present: exhaust gas energy is not recovered, so for as regards the exhaust system, it is like the one of a naturally aspirated engine, with the benefits of fast catalyst heating and engine sound optimization. This also means that all the energy, required to pressurize air in the intake line, is provided by the battery through the electric motor: for this reason, the system is well suited for a hybrid powertrain, where the electrical energy can be recovered during braking phases or also at partial loads, depending on the required torque, engine operating region and control strategy. Moreover, in order to keep the intake line relatively simple and have an easy integration with the current engine, the intention is not to have the intercooler after the compressor; this leads to a limited maximum boost pressure together with the necessity of a cooling system for the motor and the compressor, such that the air temperature does not become excessively high.
The feasibility and the performance of the system are studied with software simulations: the program GT-Suite is used to build a 1-D model of engine parts together with its intake and exhaust lines. It is then possible to understand whether the modelled powertrain respects the imposed limits in terms of pressures and temperatures, and to develop an effective control strategy to make the compressor working correctly. The 1-D model is then integrated into a co-simulation environment (developed in Simulink) for coupling the detailed engine model with a preliminary control strategy, that has the final aim to manage the power delivered to the electric motor to target an imposed value of the air pressure inside the intake manifold.
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Abstract
In recent years, the automotive sector has faced a deep change towards electrification. On the one hand, new technologically advanced battery electric vehicles (BEV) have made their appearance on the industrial market, while, on the other hand, traditional internal combustion engine vehicles (ICE vehicles) have undergone deep changes in their architecture. This is due to the possibility of coupling the internal combustion engine with electric motors in different configurations, which has enabled a considerable gain in the efficiency of powertrains, resulting in lower specific fuel consumption, and so, in lower greenhouse gas emissions. In particular, parallel hybrid and power split hybrid configurations are those most promising that have gained popularity in the last decade: indeed, for what concerns passenger cars, they represent a contribution to engine downsizing, together with the application of turbocharging technology, enabling the possibility to have “engine-on-demand”, operating in conditions near its maximum efficiency for most of the time. Moreover, parallel hybrid is also used in high-performance cars and in motorsports applications, because it enhances vehicle performances, thanks to the high-torque availability of electric motors at low speeds and to the possibility of recovering energy that would be lost otherwise, both mechanical (MGU-K recovery system) and thermal (MGU-H recovery system).
The aim of this thesis is to present a study concerning the application of an electrically actuated compressor on a high-performance internal combustion engine, exploiting the concept of e-boost. This technology eliminates problems of turbo-lag and enables the usage of compressors working also at relatively low engine speeds. This type of configuration is not new, some studies have been made in the past concerning the application of e-boost on downsized passenger cars; in this case, however, this technology is studied for a high-displacement ICE, originally naturally aspirated, whose performances in terms of torque availability need to be improved. Furthermore, to avoid adding complexity to the exhaust line, the turbine is not present: exhaust gas energy is not recovered, so for as regards the exhaust system, it is like the one of a naturally aspirated engine, with the benefits of fast catalyst heating and engine sound optimization. This also means that all the energy, required to pressurize air in the intake line, is provided by the battery through the electric motor: for this reason, the system is well suited for a hybrid powertrain, where the electrical energy can be recovered during braking phases or also at partial loads, depending on the required torque, engine operating region and control strategy. Moreover, in order to keep the intake line relatively simple and have an easy integration with the current engine, the intention is not to have the intercooler after the compressor; this leads to a limited maximum boost pressure together with the necessity of a cooling system for the motor and the compressor, such that the air temperature does not become excessively high.
The feasibility and the performance of the system are studied with software simulations: the program GT-Suite is used to build a 1-D model of engine parts together with its intake and exhaust lines. It is then possible to understand whether the modelled powertrain respects the imposed limits in terms of pressures and temperatures, and to develop an effective control strategy to make the compressor working correctly. The 1-D model is then integrated into a co-simulation environment (developed in Simulink) for coupling the detailed engine model with a preliminary control strategy, that has the final aim to manage the power delivered to the electric motor to target an imposed value of the air pressure inside the intake manifold.
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