There is no single choice regarding the materials commonly employed in the automotive industry. The most common metallic materials are steel, cast iron, aluminium and titanium. The choice is guided by the thermomechanical performances required, by the technological constraints and by the production costs. In particular for high-performance engines, the most common materials used for piston and cylinder liner are steel and aluminium. This thesis aims at analysing and comparing the effects of possible material choices on the interaction between piston and cylinder liner. The main tool adopted for performing these analyses is the Finite Element simulation. First, a motorcycle engine is considered and two possible pistons are examined: one in aluminium and the second variant in steel. This engine is equipped with both aluminium piston and cylinder liner as standard. It is therefore necessary to design a steel piston that is structurally equivalent to the aluminium one with a comparable mass. The technology designated for the production of the steel piston is Additive Manufacturing. This production technique grants wide design freedom to the shape of the component concerned. For this reason, a methodology for the design of a new piston is developed and applied using Topological Optimization techniques. The steel piston is structurally comparable to the aluminium one, but with the advantage of being able to withstand higher pressures and temperatures in the combustion chamber. At the same time, the geometry of the steel cylinder liner is achieved simply by thinning the aluminium component in order to obtain two structurally equivalent components. Having identified the system and the four possible combinations of coupling between piston and cylinder liner, each considered in the two variants of applied material, Finite Element simulations are performed. The components required for this analysis are the engine head, the engine block, the bolts, the gasket, the upper part of the crank mechanism and the cylinder liner. First of all, it is necessary to carry out a thermal analysis of the assembly, because the interaction between the components, in particular gap, interference fit and contact pressures, depends on their thermal deformation. Consequently, it is necessary to obtain the temperature field of the assembly considering both the heat generated by combustion and friction and the heat removed by the oil, by the water circuit and by the air surrounding the engine. Thereafter, a thermo-structural analysis is carried out simulating both the assembly of the engine and its operating condition. This last analysis shows great complexity from a computational point of view; for this reason, a methodology is developed and applied to lighten these calculations without losing the accuracy of the solutions. From the results of these simulations, it is possible to evaluate gap and interference with the variation of the materials and it is also possible to evaluate the stress field and the fatigue safety factor of the components involved in the analyses. The methodologies explained in this work show results that can guide the choice of materials to be used in the piston-cylinder liner coupling. Furthermore, the simplifying techniques illustrated in this thesis can be applied to any traditional engine also to speed up the thermomechanical analyses of other components such as engine head and block.

Non esiste una scelta univoca riguardo ai materiali impiegati in ambito motoristico. I materiali metallici più comuni sono acciaio, ghisa, alluminio e titanio. La scelta viene guidata dalle performance termomeccaniche richieste, dai vincoli tecnologici e dai costi di produzione. In particolare per motori ad elevate prestazioni, i materiali più comuni usati per pistone e canna cilindro sono acciaio e alluminio. Questo lavoro di tesi si pone l’obiettivo di analizzare e confrontare gli effetti delle possibili scelte di materiale sull’interazione tra pistone e canna cilindro. Lo strumento principale in queste analisi è la simulazione agli Elementi Finiti. Per cominciare è stato considerato un motore motociclistico e sono stati esaminati due possibili pistoni: uno in alluminio ed una seconda variante in acciaio. Questo motore viene equipaggiato di serie con pistone e canna cilindro in alluminio. È stato quindi necessario progettare un pistone in acciaio che fosse strutturalmente equivalente a quello in alluminio e che presentasse una massa equiparabile al pistone di serie. La tecnologia designata per la realizzazione del pistone in acciaio è l’Additive Manufacturing. Questa tecnica produttiva concede una vasta libertà progettuale alla forma del componente interessato. Per questo motivo è stata ideata ed applicata una metodologia per la progettazione di nuovo pistone utilizzando tecniche di Ottimizzazione Topologica. Il pistone in acciaio è strutturalmente equiparabile a quello in alluminio, ma con il vantaggio di poter sopportare pressioni e temperature in camera di combustione più elevate. Allo stesso tempo, la geometria della canna cilindro in acciaio è stata ottenuta semplicemente assottigliando il componente in alluminio al fine di ottenere due componenti strutturalmente equivalenti. Identificato il sistema e le quattro possibili combinazioni di accoppiamento tra pistone e canna cilindro, ognuna considerata nelle due varianti di materiale applicato, si è passati alla simulazione agli Elementi Finiti. I componenti necessari a questa analisi sono la testata motore, il basamento, le viti prigionieri, la guarnizione, la parte alta del manovellismo di spinta e la canna cilindro. Innanzitutto, è necessario svolgere un’analisi termica dell’assieme, perché l’interazione tra i componenti, in particolare giochi, interferenze e pressioni di contatto, dipendono dalla loro deformazione termica. Di conseguenza è stato necessario ricavare una mappa termica dell’assieme considerando sia i contributi dei flussi termici entranti, come combusione e attriti, sia i flussi di calore uscente asportato ad esempio dall’olio, dal circuito di raffreddamento e dall’aria che circonda il motore. In seguito, è stata svolta un’analisi termostrutturale simulando sia l’assemblaggio del motore, sia il funzionamento dello stesso. Quest’ultima analisi mostra una grande complessità dal punto di vista computazionale, per questo motivo è stata ideata ed applicata una metodologia per alleggerire questi calcoli senza perdere accuratezza nelle soluzioni. Dai risultati di queste simulazioni è stato possibile valutare giochi ed interferenze al variare dei materiali ed è stato anche possibile valutare lo stato tensionale e i coefficienti di sicurezza a fatica dei componenti coinvolti nelle analisi. Le metodologie esposte in questo lavoro mostrano risultati che possono guidare la scelta dei materiali da utilizzare nell’accoppiamento del pistone con la canna cilindro. Inoltre, le tecniche semplificative illustrate in questo lavoro di tesi potranno essere applicate a qualsiasi motore tradizionale per velocizzare le analisi termomeccaniche anche di altri componenti come testata e basamento.

Sviluppo di modelli numerici per l’analisi dell’interazione canna pistone in motori ad elevate prestazioni / Saverio Giulio Barbieri , 2021 May 18. 33. ciclo, Anno Accademico 2019/2020.

Sviluppo di modelli numerici per l’analisi dell’interazione canna pistone in motori ad elevate prestazioni

BARBIERI, SAVERIO GIULIO
2021

Abstract

There is no single choice regarding the materials commonly employed in the automotive industry. The most common metallic materials are steel, cast iron, aluminium and titanium. The choice is guided by the thermomechanical performances required, by the technological constraints and by the production costs. In particular for high-performance engines, the most common materials used for piston and cylinder liner are steel and aluminium. This thesis aims at analysing and comparing the effects of possible material choices on the interaction between piston and cylinder liner. The main tool adopted for performing these analyses is the Finite Element simulation. First, a motorcycle engine is considered and two possible pistons are examined: one in aluminium and the second variant in steel. This engine is equipped with both aluminium piston and cylinder liner as standard. It is therefore necessary to design a steel piston that is structurally equivalent to the aluminium one with a comparable mass. The technology designated for the production of the steel piston is Additive Manufacturing. This production technique grants wide design freedom to the shape of the component concerned. For this reason, a methodology for the design of a new piston is developed and applied using Topological Optimization techniques. The steel piston is structurally comparable to the aluminium one, but with the advantage of being able to withstand higher pressures and temperatures in the combustion chamber. At the same time, the geometry of the steel cylinder liner is achieved simply by thinning the aluminium component in order to obtain two structurally equivalent components. Having identified the system and the four possible combinations of coupling between piston and cylinder liner, each considered in the two variants of applied material, Finite Element simulations are performed. The components required for this analysis are the engine head, the engine block, the bolts, the gasket, the upper part of the crank mechanism and the cylinder liner. First of all, it is necessary to carry out a thermal analysis of the assembly, because the interaction between the components, in particular gap, interference fit and contact pressures, depends on their thermal deformation. Consequently, it is necessary to obtain the temperature field of the assembly considering both the heat generated by combustion and friction and the heat removed by the oil, by the water circuit and by the air surrounding the engine. Thereafter, a thermo-structural analysis is carried out simulating both the assembly of the engine and its operating condition. This last analysis shows great complexity from a computational point of view; for this reason, a methodology is developed and applied to lighten these calculations without losing the accuracy of the solutions. From the results of these simulations, it is possible to evaluate gap and interference with the variation of the materials and it is also possible to evaluate the stress field and the fatigue safety factor of the components involved in the analyses. The methodologies explained in this work show results that can guide the choice of materials to be used in the piston-cylinder liner coupling. Furthermore, the simplifying techniques illustrated in this thesis can be applied to any traditional engine also to speed up the thermomechanical analyses of other components such as engine head and block.
Development of numerical methodologies for the analysis of the piston liner interaction in high-performance engines
18-mag-2021
BASSOLI, Elena
GIACOPINI, Matteo
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11380/1245522
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