3D mechanical and thermal analysis of an Aluminium piston for a high-speed Diesel laboratory engine Master thesis in Energy Technology Thermal Engines Steinar Haugland University of Bergen Geophysical Institute Western Norway University of Applied Sciences Department of Mechanical and Marine Engineering Bergen, 01.18 3D mechanical and thermal analysis of an Aluminium piston for a high-speed Diesel laboratory engine Steinar Haugland University of Bergen (UiB) Faculty of Mathematics and Natural Sciences Geophysical Institute Postboks 7803 5020 Bergen, Norway In cooperation with: Western Norway University of Applied Sciences (HVL) Faculty of Engineering and Science Department of Mechanical and Marine Engineering Postboks 7030 5020 Bergen, Norway Norwegian title: 3D mekanisk og termisk analyse av et Aluminium- stempel til en hurtigløpende Diesel laboratoriemotor Author, student number: Steinar Haugland, 200553 Study programme: Energy technology, Thermal engines Date: 01.18 Main supervisor (HVL/UIB): Richard J. Grant Co-supervisor (HVL): Lars Magne Nerheim Client: HVL Preface The master’s programme in Energy Technology is a co-operation between the Western Norway University of Applied Sciences (HVL) and the University of Bergen (UiB). The specialization for this work is Thermal Engines. I would like to thank my supervisor, Prof.
Grant for his guidance from start to finish and his advice in regards to the finite element method, and my co-supervisor Lars Magne Nerheim for his valuable input about the engine, and earlier works on piston strength analysis. I would also like to thank Harald Moen for his help with providing experimental data from the engine, and the necessary instruments for doing measurements of the piston. I would also like to thank everyone at room D425. Their friendship, moral support and productive discussions was a great help and source of motivation while writing this masters thesis.
Finally I want to thank my family and friends, for supporting and motivating me during my time as a student. iii Steinar Haugland iv 3D mechanical and thermal analysis of an Al piston for a high-speed Diesel lab engine Abstract A cast aluminium piston of a single cylinder Petter Diesel engine is modelled using the finite element method. The engine is intended to be supercharged, which will increase the thermal loading on the piston, and so the purpose of this work is to investigate the piston behaviour and strength when subjected to the current level of thermomechanical load. The dimensions of the piston and piston pin is measured, and the materials and boundary conditions are measured, calculated or assumed.
Areas of particular interest were the combustion bowl rim and the piston pin boss. The latter was modelled using a contact interaction between the pin and boss, in order to accurately represent its behaviour. The final model is used to investigate the behaviour of the piston, locate the most critically stressed areas and the cyclical stress variations which may lead to fatigue. Lo- cal fatigue strength of the material is compared with local stress variations, and it is found that the piston is not exceeding its fatigue strength at any point and its expected lifetime should be quite high for the current loading of the engine.
v Steinar Haugland vi 3D mechanical and thermal analysis of an Al piston for a high-speed Diesel lab engine Sammendrag Et støpt aluminiumsstempel til en en-sylindret Petter Diesel motor er modellert ved bruk av elementmetoden. Det er planlagt at motoren skal superlades, noe som vil øke den termiske belastningen på stempelet. Formålet med dette arbeidet er å undersøke stempelets oppførsel og styrke under den nåværende termomekaniske belastningen. Di- mensjonene på stempelet er målt, og materialer og grensebetingelser er målt, beregnet eller antatt.
Spesielt interessante områder er kanten på forbrenningsskålen, og navet til krysspin- nen. Sistenevnte ble modellert ved bruk at en kontakt-interaksjon mellom navet og krysspinnen, for å få en nøyaktig fremstilling av oppførselen til navet. Den endelige modellen er brukt for å undersøke oppførselen til stempelet, finne de mest utsatte områdene, og de sykliske stressendringene som kan føre til utmatting. Den lokale utmattingsfastheten til materialet er sammenlignet med de lokale stressendringene, og det er funnet ut at stempelet ikke overskrider utmattingsfastheten sin på noe punkt, noe som antyder en relativt høy levetid for stempelet under den nåværende belastningen.
vii Steinar Haugland viii 3D mechanical and thermal analysis of an Al piston for a high-speed Diesel lab engine Contents 1 Introduction 1 1.1 The diesel engine piston system .2 Finite element analysis and Abaqus .2 Contact modelling in Abaqus .1 Fundamental heat transfer concepts .2 Heat transfer analysis .1 Fundamental mechanical concepts .6 Types of wear .1 Geometry of the piston .2 The boundary conditions .1 Mechanical boundary conditions .2 Thermal boundary conditions .4 The final model .1 Creating the mesh .2 Adding material properties .4 Adding the thermal boundary conditions .5 Calibration of the thermal boundary conditions .6 Adding the mechanical boundary conditions. 62 ix Steinar Haugland 3.9 Verifying the final model .1 General behaviour of the model .1 The pin boss .2 The combustion bowl rim .1 General behaviour of the model .1 The pin boss .2 The combustion bowl rim. 86 6 Conclusion 88 7 Further work 89 8 References 90 A Material properties 95 B Drawings 97 x 3D mechanical and thermal analysis of an Al piston for a high-speed Diesel lab engine 1 Introduction 1.1 Background The piston is often referred to as the heart of the reciprocating combustion engine. It is subjected to both thermal and mechanical loading, and plays a central role in convert- ing thermal energy from the combustion into mechanical energy and transferring it to the crankshaft.
Due to the high compression ratios, compared with other engine types, Diesel engines in particular subject the piston to very high stress levels. The Thermal Machines Laboratory at HVL is equipped with a Petter Diesel lab en- gine in the PH range to be used for educational purposes. The Petter Diesel PH range consist of the air-cooled engines PH1 and PH2, and the water-cooled models PH1W and PH2W. Known to be robust and simple in design, the PH range of engines can be trusted to operate for very long periods of time.
[1] The engine at the HVL Thermal Machines Laboratory is of the type PH1W, and was built around 1960. It is a four-stroke, water-cooled, naturally aspirated (NA), single- cylinder diesel engine producing 6.4 kW of power when running at 2000 rpm. Because it was built to run on lower quality fuels than what is available today, it is very robust and suitable for experiments. Recently it was modified with a common rail (CR) injection system, and there are plans supercharge the engine in the future, which would further increase the loading on the engine.[2] In order to proceed safely, it is necessary to know how the piston is handling the current thermal and mechanical loading.
Historically component strength has been investigated using measurements, but it is now commonplace to use numerical methods, in particular the finite element method (FEM). The idea behind FEM is to divide the body into a finite set of elements con- nected by nodes, apply loads and boundary conditions, and solve the equations for the resulting system to obtain approximations for quantities of interest. FEM may be used for problems involving, but not limited to, stress and heat transfer. Normally the accu- racy increases with the number of nodes used.2 Aim To investigate the effects of thermal and mechanical loading of an aluminium Diesel engine piston using the finite element method.
The analysis will be conducted based on the assumption of a steady working state of the engine.3 Objectives • Conduct a literature search for relevant and related supporting knowledge to be- come familiar with the topic of this research and to assess the current knowledge in this field. 1 Steinar Haugland • Become familiar with the finite element software package ABAQUS along with the modelling techniques required to build a representative model of the part. • Acquire realistic boundary conditions, dimensions and material properties to be used as input for the model, and explain the validity and accuracy of these quan- tities. • Produce a FEM model of the Petter Diesel engine piston and pin, and perform a convergence study and verification test in order to confirm that the model is representative of the real system.
• Use the model to investigate the behaviour of the piston, find the critically stressed areas and conduct a fatigue analysis for these areas.4 Novelty While using finite element analysis to verify the strength of a piston has been done nu- merous times before, this work attempts to give a description of the overall behaviour of the piston, and to describe the results in greater depth. In particular the stress distribution in the pin boss is looked into, including the dif- ferences between thermal loading and combined thermal and mechanical loading. The literature on this seem to be quite sparse and almost no FEM analysis has been done to look at this important area in a great level of detail. 2 3D mechanical and thermal analysis of an Al piston for a high-speed Diesel lab engine 2 Supporting literature 2.1 The diesel engine piston system The diesel engine piston interacts directly with multiple other components in the engine.
In order to get a more complete understanding of the piston, it is important to be familiar with the full piston assembly. Figure 1: The engine piston assembly.[4] As shown in Figure 1, the piston is interacting with the cylinder liner, the piston rings and the piston pin. The piston pin connects the connecting rod to the piston. All these components are introduced and explained in some detail in this chapter.1 Piston The piston plays an important role in any reciprocating engine.
It converts the thermal energy from the fuel into mechanical energy and transfers it to the crankshaft. Together with the piston rings it must seal the combustion chamber against the passage of gas and the inflow of lubrication oil, and it needs to achieve all these goals under a varied set of operating conditions. 3 Steinar Haugland Figure 2: Example of a diesel engine piston.[5] A typical piston is shown in Figure 2. The top area of the piston is called the piston crown.
For a diesel engine piston, the combustion bowl is typically located in the piston crown, and it is often the most thermally stressed part of the piston. The shape of the combustion bowl is used to control the flow pattern of the injected fuel in order to increase the efficiency of the combustion. The shape may vary depending on the config- uration of the fuel injector and air/exhaust valves. The ring belt surrounds the top part of the piston and contains grooves for the pis- ton rings.
The parts of the ring belt between two ring grooves are called lands. The top of the piston crown is called the top land, followed by the top piston ring groove, and then followed by the 2nd land, etc. Sometimes a new material, such as cast iron, is inserted around the piston groove (usually only the top piston groove) in order to provide reinforcement. The lower part of the piston is called the piston skirt, and its role is to guide the piston through the cylinder.
The skirt needs to bear the stresses between the piston and cylinder walls, and it also needs to elastically adapt to the deformations of the cylinder. In some pistons the skirt surface is made a significantly thinner in order to decrease the mass of the piston. The piston pin boss contains the piston pin (also known as a gudgeon pin or wrist pin), which connects the connecting rod to the piston. There are two options for con- necting the piston pin in the boss.
Either a shrink fit (used to be common) or a floating design where the pin may be inserted at room temperature (most common today). This is where the piston force is transmitted to the connecting rod, and is one of the highly stressed zones of the piston.