During this thesis work a Computational Fluid Dynamics (CFD) approach was chosen to simulate the steady state flow bench for a cylinder head of a modern heavy-duty Diesel engine. A steady state flow bench can provide very useful information regarding the phenomena occurring during the intake stroke of an operating engine, without incurring in complexities due to the movement of the engine piston and valves mechanism. CFD nowadays represents a valuable tool in engineering problems, capable even to replace many of the experimental tests. Experimental results related to the flow bench of the heavy-duty Diesel engine were provided by Fiat Power Train (FPT), along with simulations results achieved by means of a widely used commercial CFD code (STAR-CCM+). Within this context, the purpose of the thesis work was to validate the open source CFD OpenFOAM code (used at the Internal Combustion Engines Group of Politecnico di Milano for research activities) for steady state flow bench process of the specifically adopted engine geometry. After a theoretical introduction to the intake phase of operating four-stroke Diesel engines and to the different types of charge motions, the equations which govern a CFD model are discussed before that the simulations of the work are presented. About the latter, it was necessary to generate the computational grid (mesh) for the adopted engine and the programs used for this purpose are the open source snappyHexMesh and cfMesh. Initially, parameters specifically related to the engine flow bench (mass flow rate, discharge coefficient and swirl intensity) were evaluated, while the second step of the work was the computation of the angular momentum associated at the swirl flow, imposed in the cylinder engine during the flow bench process. The data obtained with OpenFOAM were finally compared with those achieved with STAR-CCM+ and with the experimental values provided by FPT. Lastly, it was important to provide reliable results for OpenFOAM by means of fast and cheap to run on an industrial and commercial scale CFD simulations.
In questo lavoro di tesi il flussaggio stazionario della testa di un moderno motore Diesel è stato eseguito mediante l’utilizzo di tecniche di Fluido Dinamica Computazionale (CFD). Un’operazione di flussaggio stazionario può fornire informazioni molto importanti riguardo ai fenomeni che avvengono durante la fase di aspirazione di un motore reale, senza però essere soggetta a complessità di realizzazione dovute al moto del pistone e dei meccanismi correlati alle valvole. Ad oggi, la CFD rappresenta uno strumento essenziale per la risoluzione di problemi ingegnerestici ed è in grado di poter sostituire molte tipologie di test sperimentali. I risultati sperimentali relativi al flussaggio stazionario del motore Diesel in esame sono stati forniti da Fiat Power Train (FPT) assieme ai risultati delle rispettive simulazioni, eseguite per mezzo di un codice CFD commerciale molto diffuso (STAR-CCM+). In questo contesto, l’obiettivo del presente studio è stato quello di validare OpenFOAM (codice CFD open source utilizzato al Gruppo Motori a Combustione Interna del Politecnico di Milano per attività di ricerca) per il processo di flussaggio stazionario relativo allo specifico motore adottato per questo lavoro. Dopo un’introduzione teorica sulla fase di aspirazione dei reali motori Diesel a quattro tempi e sulle possibili diverse tipologie di moto della carica nel cilindro, prima di presentare le simulazioni eseguite durante il lavoro di tesi, vengono discusse le equazioni che governano i modelli CFD. In relazione alle simulazioni, è stato necessario creare la griglia di calcolo (mesh) per il tipo di motore in uso e, a tale scopo, sono stati utilizzati due differenti software open source, chiamati rispettivamente snappyHexMesh e cfMesh. Inizialmente sono stati calcolati i parametri specifcamente associati all’operazione di flussaggio stazionario (porata, coefficiente d’efflusso e intensità di swirl) mentre, in un secondo tempo, principale obiettivo dello studio è divenuta la verifica della conservazione del momento angolare associato al moto di swirl, imposto nel cilindro del motore durante la fase di aspirazione stazionaria. I risultati ottenuti con OpenFOAM sono stati infine confrontati con quelli raggiunti per mezzo di STAR-CCM+ e con i relativi valori sperimentali forniti da FPT. Infine, è stato importante riuscire a fornire, mediante OpenFOAM, risultati non solo affidabili ma anche ottenuti per mezzo di simulazioni poco costose dal punto di vista computazionale, e quindi eseguibili a livello industriale e commerciale.
CFD simulations of the steady state flow in modern cylinder heads for heavy duty Diesel engines
PAREDI, DAVIDE
2014/2015
Abstract
During this thesis work a Computational Fluid Dynamics (CFD) approach was chosen to simulate the steady state flow bench for a cylinder head of a modern heavy-duty Diesel engine. A steady state flow bench can provide very useful information regarding the phenomena occurring during the intake stroke of an operating engine, without incurring in complexities due to the movement of the engine piston and valves mechanism. CFD nowadays represents a valuable tool in engineering problems, capable even to replace many of the experimental tests. Experimental results related to the flow bench of the heavy-duty Diesel engine were provided by Fiat Power Train (FPT), along with simulations results achieved by means of a widely used commercial CFD code (STAR-CCM+). Within this context, the purpose of the thesis work was to validate the open source CFD OpenFOAM code (used at the Internal Combustion Engines Group of Politecnico di Milano for research activities) for steady state flow bench process of the specifically adopted engine geometry. After a theoretical introduction to the intake phase of operating four-stroke Diesel engines and to the different types of charge motions, the equations which govern a CFD model are discussed before that the simulations of the work are presented. About the latter, it was necessary to generate the computational grid (mesh) for the adopted engine and the programs used for this purpose are the open source snappyHexMesh and cfMesh. Initially, parameters specifically related to the engine flow bench (mass flow rate, discharge coefficient and swirl intensity) were evaluated, while the second step of the work was the computation of the angular momentum associated at the swirl flow, imposed in the cylinder engine during the flow bench process. The data obtained with OpenFOAM were finally compared with those achieved with STAR-CCM+ and with the experimental values provided by FPT. Lastly, it was important to provide reliable results for OpenFOAM by means of fast and cheap to run on an industrial and commercial scale CFD simulations.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/109063