The Free-Piston Linear Generator (FPLG) is a new concept of internal combustion engine that could help society overall to make a transition towards more sustainable and eco-friendly energy scenarios. Its working principle is based on a cylinder-piston system directly connected to a Linear Electric Machine (LEM). Even though it is still an energy conversion system based on internal combustion, the lack of the crankshaft mechanism reduces the inertia, the weight and the friction losses of the device, resulting in an increase of the conversion efficiency from chemical to mechanical energy and consequently from chemical to electric. It’s moreover possible to exploit different compression ratios and thus different fuels without any hardware modification. The system turns out to be light and compact with low friction and vibrations, low emissions and environmentally compatible. This thesis starting from the peculiar features of the FPLG, its strengths and weaknesses, aims to develop a model to describe with a good level of detail the entire energy conversion system, providing at the same time an overview of the possible applications. Starting from the mathematical equations and formulas that dictate the behaviour of each component, the stable continuous operation of the FPLG has been simulated and achieved in OpenFOAM. A particular attention is devoted to the modelling of the linear electric machine’s behaviour and its contribution to the dynamic equilibrium acting on the piston. Once the results are validated, the focus is then moved on making induced voltages and currents suitable for a load. The control system for an active rectifier has been implemented in Simulink in order to process the direct conversion of the non-sinusoidal outputs of the LEM into regulated and stable DC-signal. A great emphasis is placed in this part on the algorithm that allows to select instant by instant the most suitable switching pattern of the rectifier's to enhance efficiency and performance.
Il generatore lineare Free-Piston (FPLG) è un nuovo tipo di motore a combustione interna che potrebbe aiutare la società verso una transizione a scenari energetici più sostenibili ed ecocompatibili. Basa il suo principio di funzionamento su un sistema cilindro-pistone direttamente accoppiato con una macchina elettrica di tipo lineare (LEM). Pur essendo un sistema di conversione dell’energia ancora basato sulla combustione, l’assenza di un manovellismo riduce le inerzie in gioco, il peso e le perdite di attrito con il risultato di aumentare significativamente l’efficienza di conversione dell’energia da chimica a meccanica e di conseguenza anche da chimica ad elettrica. È inoltre possibile sfruttare diversi rapporti di compressione e dunque diverse tipologie di carburante senza alcun tipo di aggiunta o modifica strutturale. Si ottiene dunque un sistema leggero, compatto con poche vibrazioni, emissioni e compatibile a livello ambientale. Questa tesi partendo dalle caratteristiche salienti del Free-Piston Linear Generator (FPLG), dai suoi punti di forza e dalle sue criticità, ha l’obiettivo di sviluppare un modello che permetta di rappresentare con un buon grado di dettaglio il funzionamento dell’intero sistema di conversione dell’energia, fornendo una visione d’insieme delle possibili applicazioni. Partendo dalle equazioni matematiche e dalle formule che governano il comportamento di ogni componente, è stato quindi simulato in OpenFOAM il comportamento a regime del FPLG. Una particolare attenzione è riposta nella modellizzazione della macchina elettrica lineare e al suo contributo all’equilibrio dinamico che si instaura sul pistone. Una volta validati i risultati, ci si è interessati poi a rendere correnti e tensioni indotte adatte all’alimentazione di un carico. È stato quindi implementato in Simulink il sistema di controllo di un active rectifier in grado di convertire le uscite non sinusoidali della macchina elettrica in un segnale stabile in corrente continua. Una grande enfasi è posta in questa parte sull’algoritmo che permette istante per istante di individuare la migliore configurazione degli interruttori in termini di efficienza e prestazioni.
Free-piston generator : modelling of a spark-ignition engine, design of the linear electric machine and active rectifier control
Fasana, Francesco;Facheris, Andrea
2020/2021
Abstract
The Free-Piston Linear Generator (FPLG) is a new concept of internal combustion engine that could help society overall to make a transition towards more sustainable and eco-friendly energy scenarios. Its working principle is based on a cylinder-piston system directly connected to a Linear Electric Machine (LEM). Even though it is still an energy conversion system based on internal combustion, the lack of the crankshaft mechanism reduces the inertia, the weight and the friction losses of the device, resulting in an increase of the conversion efficiency from chemical to mechanical energy and consequently from chemical to electric. It’s moreover possible to exploit different compression ratios and thus different fuels without any hardware modification. The system turns out to be light and compact with low friction and vibrations, low emissions and environmentally compatible. This thesis starting from the peculiar features of the FPLG, its strengths and weaknesses, aims to develop a model to describe with a good level of detail the entire energy conversion system, providing at the same time an overview of the possible applications. Starting from the mathematical equations and formulas that dictate the behaviour of each component, the stable continuous operation of the FPLG has been simulated and achieved in OpenFOAM. A particular attention is devoted to the modelling of the linear electric machine’s behaviour and its contribution to the dynamic equilibrium acting on the piston. Once the results are validated, the focus is then moved on making induced voltages and currents suitable for a load. The control system for an active rectifier has been implemented in Simulink in order to process the direct conversion of the non-sinusoidal outputs of the LEM into regulated and stable DC-signal. A great emphasis is placed in this part on the algorithm that allows to select instant by instant the most suitable switching pattern of the rectifier's to enhance efficiency and performance.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/183182