Critical Component Wear in Heavy Duty Engines E-Book

P. A. Lakshminarayanan

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 721

Veröffentlichungsjahr: 2011

Beschreibung

The critical parts of a heavy duty engine are theoretically designed for infinite life without mechanical fatigue failure. Yet the life of an engine is in reality determined by wear of the critical parts. Even if an engine is designed and built to have normal wear life, abnormal wear takes place either due to special working conditions or increased loading. Understanding abnormal and normal wear enables the engineer to control the external conditions leading to premature wear, or to design the critical parts that have longer wear life and hence lower costs. The literature on wear phenomenon related to engines is scattered in numerous periodicals and books. For the first time, Lakshminarayanan and Nayak bring the tribological aspects of different critical engine components together in one volume, covering key components like the liner, piston, rings, valve, valve train and bearings, with methods to identify and quantify wear. * The first book to combine solutions to critical component wear in one volume * Presents real world case studies with suitable mathematical models for earth movers, power generators, and sea going vessels * Includes material from researchers at Schaeffer Manufacturing (USA), Tekniker (Spain), Fuchs (Germany), BAM (Germany), Kirloskar Oil Engines Ltd (India) and Tarabusi (Spain) * Wear simulations and calculations included in the appendices * Instructor presentations slides with book figures available from the companion site Critical Component Wear in Heavy Duty Engines is aimed at postgraduates in automotive engineering, engine design, tribology, combustion and practitioners involved in engine R&D for applications such as commercial vehicles, cars, stationary engines (for generators, pumps, etc.), boats and ships. This book is also a key reference for senior undergraduates looking to move onto advanced study in the above topics, consultants and product mangers in industry, as well as engineers involved in design of furnaces, gas turbines, and rocket combustion. Companion website for the book: href="http://www.wiley.com/go/lakshmi">www.wiley.com/go/lakshmi

Leseprobe

Contents

Cover

Title Page

Copyright

List of Contributors

Preface

Acknowledgements

Part I: Overture

Chapter 1: Wear in the Heavy Duty Engine

1.1 Introduction

1.2 Engine Life

1.3 Wear in Engines

1.4 General Wear Model

1.5 Wear of Engine Bearings

1.6 Wear of Piston Rings and Liners

1.7 Wear of Valves and Valve Guides

1.8 Reduction in Wear Life of Critical Parts Due to Contaminants in Oil

1.9 Oils for New Generation Engines with Longer Drain Intervals

1.10 Filters

1.11 Types of Wear of Critical Parts in a Highly Loaded Diesel Engine

References

Chapter 2: Engine Size and Life

2.1 Introduction

2.2 Engine Life

2.3 Factors on Which Life is Dependent

2.4 Friction Force and Power

2.5 Similarity Studies

2.6 Archard's Law of Wear

2.7 Wear Life of Engines

2.8 Summary

Appendix 2.A Engine Parameters, Mechanical Efficiency and Life

Appendix 2.B Hardness and Fatigue Limits of Different Copper–Lead–Tin (Cu–Pb–Sn) Bearings

Appendix 2.C Hardness and Fatigue Limits of Different Aluminium–Tin (Al–Sn) Bearings6

References

Part II: Valve Train Components

Chapter 3: Inlet Valve Seat Wear in High bmep Diesel Engines

3.1 Introduction

3.2 Valve Seat Wear

3.3 Shear Strain and Wear due to Relative Displacement

3.4 Wear Model

3.5 Finite Element Analysis

3.6 Experiments, Results and Discussions

3.7 Summary

3.8 Design Rule for Inlet Valve Seat Wear in High bmep Engines

References

Chapter 4: Wear of the Cam Follower and Rocker Toe

4.1 Introduction

4.2 Wear of Cam Follower Surfaces

4.3 Typical Modes of Wear

4.4 Experiments on Cam Follower Wear

4.5 Dynamics of the Valve Train System of the Pushrod Type

4.6 Wear Model

4.7 Parametric Study

4.8 Wear of the Cast Iron Rocker Toe

4.9 Summary

References

Part III: Liner, Piston and Piston Rings

Chapter 5: Liner Wear: Wear of Roughness Peaks in Sparse Contact

5.1 Introduction

5.2 Surface Texture of Liners and Rings

5.3 Wear of Liner Surfaces

5.4 Wear Model

5.5 Liner Wear Model for Wear of Roughness Peaks in Sparse Contact

5.6 Discussions on Wear of Liner Roughness Peaks due to Sparse Contact

5.7 Summary

Appendix 5.A Sample Calculation of the Wear of a Rough Plateau Honed Liner

References

Chapter 6: Generalized Boundary Conditions for Designing Diesel Pistons

6.1 Introduction

6.2 Temperature Distribution and Form of the Piston

6.3 Experimental Mapping of Temperature Field in the Piston

6.4 Heat Transfer in Pistons

6.5 Calculation of Piston Shape

6.6 Summary

References

Chapter 7: Bore Polishing Wear in Diesel Engine Cylinders

7.1 Introduction

7.2 Wear Phenomenon for Liner Surfaces

7.3 Bore Polishing Mechanism

7.4 Wear Model

7.5 Calculation Methodology and Study of Bore Polishing Wear

7.6 Case Study on Bore Polishing Wear in Diesel Engine Cylinders

7.7 Summary

References

Chapter 8: Abrasive Wear of Piston Grooves in Highly Loaded Diesel Engines

8.1 Introduction

8.2 Wear Phenomenon in Piston Grooves

8.3 Wear Model

8.4 Experimental Validation

8.5 Estimation of Wear Using Sarkar's Model

8.6 Summary

References

Chapter 9: Abrasive Wear of Liners and Piston Rings

9.1 Introduction

9.2 Wear of Liner and Ring Surfaces

9.3 Design Parameters

9.4 Study of Abrasive Wear on Off-highway Engines

9.5 Winnowing Effect

9.6 Scanning Electron Microscopy of Abrasive Wear

9.7 Critical Dosage of Sand and Life of Piston–Ring–Liner Assembly

9.8 Summary

References

Chapter 10: Corrosive Wear

10.1 Introduction

10.2 Operating Parameters

10.3 Corrosive Wear Study on Off-road Application Engines

10.4 Wear Related to Coolants in an Engine

10.5 Summary

References

Chapter 11: Tribological Tests to Simulate Wear on Piston Rings

11.1 Introduction

11.2 Friction and Wear Tests

11.3 Test Procedures Assigned to the High Frequency, Linear Oscillating Test Machine

11.4 Load, Friction and Wear Tests

11.5 Test Results

11.6 Selection of Lubricants

11.7 High Performance Bio-lubricants and Tribo-reactive Materials for Clean Automotive Applications

11.8 Tribo-Active Materials

11.9 EP Tribological Tests

11.10 Acknowledgements

References

Part IV: Engine Bearings

Chapter 12: Friction and Wear in Engine Bearings

12.1 Introduction

12.2 Engine Bearing Materials

12.3 Functions of Engine Bearing Layers

12.4 Types of Overlays/Coatings in Engine Bearings

12.5 Coatings for Engine Bearings

12.6 Relevance of Lubrication Regimes in the Study of Bearing Wear

12.7 Theoretical Friction and Wear in Bearings

12.8 Wear

12.9 Mechanisms of Wear

12.10 Requirements of Engine Bearing Materials

12.11 Characterization Tests for Wear Behaviour of Engine Bearings

12.12 Summary

References

Part V: Lubricating Oils for Modern Engines

Chapter 13: Heavy Duty Diesel Engine Oils, Emission Strategies and their Effect on Engine Oils

13.1 Introduction

13.2 What Drives the Changes in Diesel Engine Oil Specifications?

13.3 Engine Oil Requirements

13.4 Components of Engine Oil Performance

13.5 How Engine Oil Performance Standards are Developed

13.6 API Service Classifications

13.7 ACEA Specifications

13.8 OEM Specifications

13.9 Why Some API Service Classifications Become Obsolete

13.10 Engine Oil Composition

13.11 Specific Engine Oil Additive Chemistry

13.12 Maintaining and Changing Engine Oils

13.13 Diesel Engine Oil Trends

13.14 Engine Design Technologies and Strategies Used to Control Emissions

13.15 Impact of Emission Strategies on Engine Oils

13.16 How Have Engine Oils Changed to Cope with the Demands of Low Emissions?

13.17 Most Prevalent API Specifications Found In Use

13.18 Paradigm Shift in Engine Oil Technology

13.19 Future Engine Oil Developments

13.20 Summary

References

Part VI: Fuel Injection Equipment

Chapter 14: Wear of Fuel Injection Equipment

14.1 Introduction

14.2 Wear due to Diesel Fuel Quality

14.3 Wear due to Abrasive Dust in Fuel

14.4 Wear due to Water in Fuel

14.5 Summary

References

Part VII: Heavy Fuel Engines

Chapter 15: Wear with Heavy Fuel Oil Operation

15.1 Introduction

15.2 Fuel Treatment: Filtration and Homogenization

15.3 Water and Chlorine

15.4 Viscosity, Carbon Residue and Dust

15.5 Deposit Build Up on Top Land and Anti-polishing Ring for Reducing the Wear of Liner, Rings and Piston

15.6 High Sulfur in Fuel

15.7 Low Sulfur in Fuel

15.8 Catalyst Fines

15.9 High Temperature Corrosion

15.10 Wear Specific to Four-stroke HFO Engines

15.11 New Engines Compliant to Maritime Emission Standards

15.12 Wear Life of an HFO Engine

15.13 Summary

References

Part VIII: Filters

Chapter 16: Air and Oil Filtration and Its Impact on Oil Life and Engine Wear Life

16.1 Introduction

16.2 Mechanisms of Filtration

16.3 Classification of Filtration

16.4 Filter Rating

16.5 Filter Selection

16.6 Introduction to Different Filters in the Engine

16.7 Oil Filters and Impact on Oil and Engine Life

16.8 Engine Wear

16.9 Full Flow Oil Filters

16.10 Summary

Appendix 16.A Filter Tests and Test Standards

References

Index

This edition first published 2011

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Library of Congress Cataloging-in-Publication Data

Lakshminarayanan, P. A.

Critical component wear in heavy duty engines / P.A. Lakshminarayanan, Nagaraj S. Nayak.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-82882-3 (hardback)

1. Internal combustion engines. 2. Machine parts–Failures. 3. Mechanical wear. I. Nayak, Nagaraj S. II.

Title.

TJ788.L35 2011

621.43028'8–dc23

2011020808

Print ISBN: 978-0-470-82882-3

ePDF ISBN: 978-0-470-82883-0

oBook ISBN: 978-0-470-82884-7

ePub ISBN: 978-0-470-82885-4

Mobi ISBN: 978-1-118-08296-6

List of Contributors

Y.V. Aghav

Kirloskar Oil Engines Limited, Pune, India

X. Fernandez

Tekniker-IK4, Avenida Otaola 20, 20.600 Eibar, Spain

Elena Fuentes

Tekniker-IK4, Eibar, Spain

A. Igartua

Tekniker-IK4, Avenida Otaola 20, 20.600 Eibar, Spain

I. Illarramendi

CIE Tarabusi, Urkizu Auzoa 58, 48140 Igorre, Spain

Kedar Kanase

Kirloskar Oil Engines Limited, Pune, India

M.N. Kumar

Kirloskar Oil Engines Limited, Pune, India

P.A. Lakshminarayanan

Ashok Leyland Limited, Engine R&D, Hosur, Tamilnadu 535126, India

Lawrence G. Ludwig

Schaeffer Manufacturing, Saint Louis, MO, USA

R. Luther

Fuchs, Petrolub AG, Friesenheimer Straße 17, 68169 Mannheim, Germany

M.V. Ganesh Prasad

Ashok Leyland Limited, Hosur, India

M.A. Ravichandran

Kirloskar Oil Engines Limited, Pune, India

M. Woydt

Federal Institute for Materials Research and Testing (BAM), D-12200 Berlin, Germany

Preface

Material wears away at the surface of an engine part when rubbed by another material under pressure. The total relative distance travelled, friction and hardness of the materials and the force determine the mass of metal removed by wear. A powerful law was formulated by Archard in 1950 describing the simple relationship between these parameters. This law is repeatedly applied in this book in different forms to estimate the wear quantitatively. Wear increases the tight clearances carefully built into a diesel engine and its critical auxiliaries. The increase in clearances beyond the design limits multiplied by a factor (usually 2) affects the efficiency of the engine parts and simultaneously increases the noise from it. When in excess, wear debris (produced at the surfaces of the critical parts) forms a very tiny fraction of the weight of the whole engine, but makes the entire machine useless. Thus, when a part reaches its critical wear limit, we can say the life of the part is finished. Hence, the study of wear phenomena in engines is important to answer philosophical questions on the life of an engine. To help reading and make the chapters more or less self-contained, some of the basic ideas on wear and friction are repeated keeping the context in mind.

Up to Chapter 10, the wear of critical parts is explained, based on observations, to understand the nature of wear with an aim to estimate wear quantitatively using models.

It appears, as shown in Chapter 2, that the bottom overhaul life is directly proportional to the square of the size of the engine and inversely to the load factor and the mean piston velocity. The larger the engine, the longer is the life of the engine. The critical parts that determine the life of an engine are the valve train, piston, cylinder liner rings and bearings. The majority of the book relates to a heavy duty normal four stroke diesel engine working off and on road.

Valve train wear affects sealing of the gases in the cylinder. They wear out due to corrosion and fretting at the seat. Archard's law is applied to estimate the guidelines for the tolerable micron-sized fretting movement and consequent wasting of the surface. Due to valve seat wear, the valve lash reduces. When the lash is consumed completely, the gases in the engine leak out past the valves that remain a crack open. Gas flow at high temperature cuts the seat and reduces the efficiency of the engine. In Chapter 3, a method to calculate the critical wear mass, beyond which the wear rate would become catastrophic, is given.

In Chapter 4, the cam wear due to high contact stress and relative velocity is explained. Calculation of Hertzian stress and the high wear zones on the cam are graphically explained. Severe boundary lubrication exists, for example, at the valve tip, rocker toe and the cam follower. A method to calculate the wear rate is provided.

The piston rings are starved of oil at the dead centres. The rings seek succour from the oil stored in the valleys of the rough liner surface. The oil not only helps in lubricating and separating the ring from the liner, thus preventing physical contact, but also evaporates, so absorbing the latent heat from the rings and hence cooling them. The design of roughness of the liner can be plateau honed or normally honed. The latter produces more debris in the initial stages and the surface slowly turns plateau. Plateau honing can be of different types. Kragelskii devised a method to calculate the wear of normally rough surfaces. In order to apply this powerful method to plateau honed liners in modern engines, a concept of ‘plateauness’ is invented in Chapter 5 and an equivalent normal roughness is derived and plugged into the Kragelskii model. Several types of honing are studied successfully for normal wear.

All the moving parts in an engine, with the exception of the pistons, grow very little relative to their mating parts because their expansion coefficients are nearly equal and the rise in temperature is rather small. However, a piston does not retain its cold shape while running, and hence the running clearances are affected. In addition, carbon, silica and oil deposits reduce clearances and affect the mechanics at the surface. Therefore, it is important to know the shape of the piston accurately when cold for manufacturing the piston and when hot for proper functioning. Both axisymmetric and fully three dimensional models with a powerful set of boundary conditions applicable to all types of diesel pistons in general are described in Chapter 6.

Chapter 7 describes wear problems when the top land of the piston touches the liner. It leads to polishing of the bore when the roughness created intentionally by honing the liner surface is completely removed and lubrication fails. The bore wear distorts the liner shape and the rings are unable to seal the oil travelling upwards into the combustion chamber. Though a separate chapter is dedicated for heavy fuel operation, the example chosen is for a heavy fuel engine. A calculation method is provided to enable the correct description of the top land and skirt profiles. For large engines running on heavy fuel, a scraper ring is the optimum solution to solve bore polishing problem, without losing performance.

Not only are the basic design of the shape, roughness and hardness of various surfaces important for the long life of an engine, but so is control of abrasives entering the engine. These are either produced by combustion and wear, or dust inhaled from the environment through filters that are less than 100% efficient. The higher the dustiness of the environment the more is the mass of dust (quartz) allowed by the filters. Chapter 8 describes the three-body wear in different piston ring grooves by inputting the measured sizes of dust collected in the grooves into the model. Every engine seems to have a critical dosage of dust that ends the life of the piston rings and the liner earlier than that determined by normal aging. It is expressed in terms of grammes of dust per litre of swept volume of the engine and seems applicable universally to all types of diesel engines.

Combustion of diesel fuel forms sulfur oxides which themselves are not corrosive. However, the water of combustion condenses on the cooler walls where the dew point is reached and forms sulfuric acid by dissolving the oxides. The acid is spread by the oil and gases flowing to different parts of the engine from the combustion chamber, causing corrosion of bearings, valve seats and steel parts like piston rings, liner and turbochargers. A narrow window on the coolant temperature, when maintained, could control the corrosive wear, as described in Chapter 10.

The sealing of gases by the piston ring is so important that coatings and materials are developed to work at high temperatures and pressures. During development, they undergo tribological tests outside the engines in engine-like conditions. The oscillation–friction–wear (SRV) device is fully exploited to characterize novel piston ring materials and coatings such as physically vapour deposited, high velocity oxi-fuel deposited coatings or plasma coatings. This enables choice of the best of a number of designs, processes and combinations of materials (Chapter 11).

Bearings hold a thin film of oil which enables transfer of high loads through the power train in a diesel engine. Chapter 12 describes the duties of the bearings, the lubrication regimes, the orbits of shafts in the journal, their tribology, characterization tests and types of bearings. Corrosive, abrasive and adhesion wear are described in detail. A concept of tribo-ecology is brought in to help resolve the dilemma faced by the designer while selecting a bearing for a given application.

In Chapter 15, what drives the changes in diesel engine oil specifications, and the roles of the governments, emissions regulations, OEM and the consumer, are discussed. The engine oil requirements, like easy starting and pumping, preventing wear, reducing friction, protection against rust and corrosion, minimizing deposits, better fuel economy, sealing high pressures, non-foaming and keeping the engine parts clean, are explained. An insight into the process of developing oil performance standards in keeping with the requirements is given. The role of base oils, how their properties are affected by the manufacturing method and additives in the oil, is explained. The emission treatment after the engine and post injection have profound influence on the design of oil, with less ash, sulfur and phosphorus indicating a paradigm shift in engine oil technology. Then telescoping into the future, the development of new generation of oil is debated.

Fuel injection equipment does not function in an engine at such a high temperature as the piston but is under extraordinary fuel pressure, as explained in Chapter 14. To save the pressure from leakage, the clearances between the metal parts are designed tight. With the advent of higher emissions norms, designers seek higher injection pressures and the clearance is reduced correspondingly. This increases the demand on the fuel filter to remove finer particles with higher efficiency. Water ingress in fuel in humid areas of operation leads to corrosion, and hence must be separated efficiently. The quality of fuel itself is changing with the reduction in sulfur (to contain emission), which reduces the lubricity of fuel hand in hand. Additivating fuel to satisfy the requirements is demanding attention of the fuel manufacturers.

Almost all of the entire commerce between nations is transported by ships that are powered by large diesel engines. Very large diesel engines work on a two-stroke cycle. The large engines invariably work on heavy fuel to save cost. In Chapter 15, the wear phenomena particular to large heavy fuel engines is considered. High sulfur, melting eutectic of catalyst fines (vanadium) and sea salt (sodium), carbon formation and acidification are some of the key characteristics that cause corrosive and other types of wear. If the thermodynamic parameters of the engine, as well as the quality and condition of oil and fuel, are not tightly controlled, premature wear can cause deterioration and bring the life of an engine to an early end. Parts of valves, turbochargers, piston and rings are described regarding corrosive and abrasive wear.

Chapter 16 is a peep into the complex world of filters. Air, fuel and oil have to be highly filtered to reduce the sand, carbon, water, metals, bacteria and other harmful material content that can cause severe wear. In most of the engines, these particles reduce the life of an engine that would otherwise age normally.

Acknowledgements

Our work at the Indian Institutes of Technology, in Madras and Delhi, helped us research into the wear of critical parts of heavy duty diesel engines. Opportunities were tremendous at Ashok Leyland Ltd and Kirloskar Oil Engines Ltd to come face to face with wear problems and solve them. We are thankful to Professor P.A. Janakiraman, Professor M.K. Gajendra Babu and Mr A.D. Dani for their support while tackling the problems. We are thankful to Mr K.L.S. Setty for encouraging us and continuous interaction and suggestions while writing this book.

Professors A. Igartua and X. Fernandez (TEKNIKER-IK4, Eibar, Spain), M. Woydt (Federal Institute for Materials Research and Testing (BAM), Berlin, Germany), R. Luther (FUCHS, Petrolub AG, Mannheim, Germany) and I. Illarramendi (CIE TARABUSI, Igorre, Spain) charmed us by accepting our request to contribute on the subject of piston rings. We are grateful to them.

We are indebted to Professor Elena Fuentes (Tekniker-IK4 Foundation, Spain) and Mr Kedar Kanase (Kirloskar Oil Engines Ltd., Pune, India) for capturing the difficult subject of engine bearings.

Oil is at the foundation of tribology of all the relatively moving parts in an engine. It transfers force and torque at pressures of high magnitude. The chemistry and function of oil in the hot and chemically active environment is complex. We are at the cusp of oil technology that is different from the past. New developments of ash-free, highly dispersant and long-life oils are created to withstand different types of oil stresses. We thankfully acknowledge the contribution of Professor Larry Ludwig (Schaeffer Manufacturing) on this important subject.

Filters of oil, air and fuel play a more and more important role in containing the wear of critical engine parts. We are thankful to our colleague Mr Ganesh Prasad for writing a capsule chapter on filters.

We thank our erstwhile colleagues at Kirloskar Oil Engines Ltd, Mr Yogesh Aghav, Dr M.N. Kumar and Mr M.A. Ravichandran, for sharing their experience and for the in-depth study of the special subject of wear in heavy fuel engines. We remember with gratitude the kind support received from S.E.M.T Pielstick during the study.

We gratefully acknowledge the encouragement by Mr Seshasayee, MD of Ashok Leyland to write this book. We thank the publisher John Wiley & Sons, and the editors James Murphy and Shelley Chow for giving us the opportunity to work on the subject of our passion and giving us all types of support to bring this book to reality. We would like to extend our special thanks to Mr. Kevin Dunn for going through all the chapters painstakingly and offering valuable comments.

P.A. LakshminarayananNagaraj S. Nayak7 February 2011

Part I

Overture

Chapter 1

Wear in the Heavy Duty Engine

1.1 Introduction

Stringent standards in different countries for both nitrogen oxides (NOx) and particulate emissions from diesel engines are becoming unified with national boundaries becoming blurred (Figure 13.1). Emissions increase with engine wear. The easily observable consequences of wear in a diesel engine are the increases in smoke and consumption of fuel and oil. An assured wear life of 8000 hours is expected for a typical off-road engine in the field. Similarly, the vehicles on the road are expected to have an assured wear life of a million kilometres or more. Running many engines in the laboratory or multiple vehicles in the field may help to establish the reliability of the engines and their life. However, it is too late to recognize a problem during these trials. To satisfy reliability, after every failure in the field the engineer is asked to run more vehicles for a geometrically increasing number of testing hours. To prove the engine reliability could take up to three years in the normal course; this is longer than the life of newer emission regimes, and hence it is costly to repeat reliability experiments. In addition, the estimation of life, even by modern reliability methods, is straddled with an error of 50%.

Modern design procedures are detailed and well established against gross failures like fatigue, breaking and loosening. Therefore, only the micron sized failures at the surfaces that result in wear affect the life of an engine. Apart from the basic design aspects that are grounds for ‘normal’ wear or aging, extreme loads, environments like a dusty atmosphere plus quality of maintenance, fuels and oils bring an earlier end to the life of an engine. If the engine that has lasted its wear life is studied, only less than 0.01% of the total mass of the engine has been wasted away. In other words, more than 99.9% of the mass has survived when the parts are replaced at the end of their wear life. If the normal and abnormal wear is understood early based on the application or design of an engine, it is possible to incorporate features and protections in the design so that the engine is able to complete its expected life with sufficient margin.

1.2 Engine Life

In a diesel engine, the critical parts that wear out are the piston and ring assembly, liners, valve train, valves and bearings. The minimum lives of these parts determine the life of an engine. In other words, the wear life of an engine can be described as the bottom overhaul interval when all the worn parts are changed. The overhaul lives of various engines of different sizes (Chapter 2 references) are plotted in Figure 1.1. The points in the figure are normalized for a common load factor of 0.8 (Chapter 2). Apparently, the life of an engine seems to be a direct function of the power produced by the engine per cylinder, which in turn depends on the size of the engine. The graph shows dependency of life of an engine on its bore.

Figure 1.1 Dependency of wear life on engine size

1.3 Wear in Engines

1.3.1 Natural Aging

At a given load and speed, the pressure and the relative velocity of the pairs of wear parts in an engine vary cyclically undergoing varying degrees of lubrication. All the wear parts in the engine are separated by a thin film of oil. During most of the cycle, the hydrodynamic pressure generated at the wedge shaped interfaces (Figure 1.2) of the pairs of wear parts is sufficient to lift the surfaces beyond their micron sized roughness. However, within a cycle, the thickness of the oil film could drop so low that the pair may come in close contact in some zones. In addition, during starting and stopping in the normal life of an engine, the parts run at a relative velocity so small that the asperities of the two wear surfaces come in contact and very high contact pressures are generated at the roughness peaks. Since the peaks are random in occurrence and shape, an element of probability is introduced in their loading and in the direction of loading on the peaks, which is not always normal to the nominal surface (Figure 1.3). The pressure bends the roughness peaks in the local direction of application of load. Even if the local stress is less than the plastic limit of the material, the asperities break away in pieces after many cycles of load, due to fatigue. If there is a special affinity between the metals of the surfaces, it is possible that metal from one surface is transferred to the other surface causing adhesive wear. Such an eventuality is not unusual in the main and connecting rod bearings, which are highly loaded every engine cycle. Therefore, wear takes place when the surfaces separated by a thin oil film come in contact during operating conditions.

Figure 1.2 Lifting pressure generated by flow of oil in the wedge between relatively moving plates

Figure 1.3 Microscopic view of the asperities of bearing surfaces in contact, where the local load is not normal to the nominal surface

1.4 General Wear Model

The wear of a wide range of material combinations has been studied in unlubricated conditions in detail for different loads and relative speeds of wear surfaces (Archard 1956). As a broad classification, two contrasting mechanisms of wear have been observed. In nearly all experiments, and for all types of wear mechanism, once equilibrium conditions are established at the surfaces, the wear rate (kg s−1) is independent of the apparent area of contact. The wear rate is proportional to the load with the same surface conditions. In practice, this simple relation is modified because the surface conditions depend on the load. These rules of wear may be derived, on basic grounds, from the experimental results, or from more detailed theoretical calculations on the different wear parts of an engine.

1.5 Wear of Engine Bearings

The bearing overlay of about 20 microns thickness is an alloy of tin, antimony, copper and lead. This alloy has some important properties, namely, the ability to absorb lubricating oil on the surface and hence provide lubrication when the bearing is starved, the ability to absorb small particles of dirt (embeddability) without increasing the wear of the bearing or crankshaft and seizure resistance, so that it does not weld itself to the crankshaft material even under extreme loads or high speeds. Lastly, it must be able to be run slightly out of alignment without wearing out. Also, the material enables some kind of healing in the event of mild seizure and the material is transferred back to the parent bearing. The parts are heated by friction and also by heat transfer from the hot environment (e.g. hot combustion gases). The copious amount of oil flow between the surfaces enables washing away of both the debris and the heat. These wasted metal particles are found in the oil, sump and the oil filter.

1.6 Wear of Piston Rings and Liners

Usually, today there are three rings in engines that have a swept volume less than three litres per cylinder. Larger engines have four or five rings and they are always above the piston pin. Rings below the piston pin are out-dated, as the arrangement seriously interferes with the supply of oil to the rings above the piston pin and causes excessive wear of the rings and the piston skirt. The three piston rings are nearly always made of three different materials. The oil control ring is the bottom ring and this has significant amounts of lubricant but its job is to limit the lubricant reaching the compression rings above it and this makes life a little difficult for the compression rings. Therefore, the compression rings have to work with very little oil. The lower compression ring is usually an alloy of chrome, while the top ring is usually an alloy of cast iron. In some engines, steel rings are used at the top. Wear is prevented by a thin layer of oil on the surface and oil adsorbed in the surface of the bore and piston rings. The oil film temperature at the top ring is maintained by not only the coolant but, more importantly, also by evaporation of oil trapped in the rough valleys of the liner surface. The reciprocating nature of the piston transfers some lubricant from the cylinder wall to the piston ring and this stops the pistons and rings from seizing in the bore.

1.7 Wear of Valves and Valve Guides

Valves and valve guides, especially the exhaust valve and guide, survive in the harshest environment in an engine. They operate at temperatures ranging from below freezing to as high as 1000 °C. At the valve guide, the gas is at a pressure in excess of 0.3 MPa. The gas flow coats the inside of the guide with deposits of carbon. The guide and the valve seat conduct heat away from the valve into the water jacket to prevent it from melting. The guides are sometimes made of porous sintered metals which absorb oil to lubricate and cool the valve stems.

1.8 Reduction in Wear Life of Critical Parts Due to Contaminants in Oil

In a normal engine, the natural wear is far less than the wear due to contaminants in the oil, such as the metal debris, soot contributed by combustion and the dust from environment in which the engine is working. There are almost no roller or ball bearings inside an engine of a swept volume less than three litres per cylinder because they are more susceptible to damage by contamination as well as quite noisy and expensive to produce.

The combustion gases contain acid, soot and heat. At the walls of the liner, the oil is kept relatively cool by the coolant but it faces the intense heat of combustion protected only by flame quench distances and the flow boundary layer along the wall. At very abnormal conditions like knocking, the boundary layer can be torn and penetrated by the high temperature gases instantaneously (Heywood, 1988), and the oil can become over heated. Also, the soot of combustion in diesel engines disperses in the oil. In engines using exhaust gas recirculation (EGR) and late post injection to aid regeneration of diesel particulate filters, the problem is accentuated. Contamination of lubricating oil by diesel soot is one of the major causes of increased engine wear (Totten, Westbrook and Shah, 2003), especially with EGR technology used to curb nitrogen oxides (NOx) emissions. The dispersion of the soot in oil is increased by additive packages containing zinc dithiophosphate (ZDP) for these engines (Sam, Balla and Gautam, 2007). Otherwise, in normal conditions, the oil degrades slowly by oxidation and sludge forms. The strong acids formed during combustion in the presence of water vapour dissolve in the oil and the acidity of the oil increases. The oil contains alkaline compounds to neutralize these acids. However, all the weak acids formed under heat in the oil are not neutralized, and hence oil in use is both acidic and basic at the same time. The acids cause corrosive wear. In addition, the air taken in by the engine contains dust particles of different sizes and only about 99.9% of it is filtered at the air filters. As the filter accumulates dust, its efficiency improves at the cost of increased loss in pressure across the filter element. Thus, in a new filter, 0.1% of the dust enters the engine and a small part of it is retained on the wet walls of the liner to be washed by the oil on the liner to the oil sump. The higher the concentration of the dust in the air entering the filter, the higher is the quantity of dust entering the engine as the percentage filtration remains the same for a given air filter. Excessive soot, dust and acid cause abrasive and corrosive wear of critical parts of an engine.

1.8.1 Oil Analysis

The periodic analysis of wear metals in the oil, therefore, diagnoses various parts that are wearing out in the engine and at what rate. It enables the user to take the right action in time. A comprehensive list of sources of wear metals in oil is given in Table 1.1 (Bentley Tribology Services, 2010; Totten, Westbrook and Shah, 2003).

Table 1.1 Sources of wear metals in oil.

MetalsWear Metal SourceIroncylinder liners, piston rings, valve train, crankshaft, rocker arms, spring gears, lock washers, nuts, pins, connecting rods, engine blocks, oil pump, gears, pinions, case hardened teeth, pump, motor, vanes, pump housing, cylinder bores and rods, pistons, bearings, cylinders, housing, shafts, pipingCoppervalve train bushing, wrist pin bushing, cam bushings, oil cooler core, thrust washers, governor, connecting rods bearings, valve gear train thrust buttons, oil cooler baffles, plates, thrust washers, bearings, wear plates, thrust washers, oil pump, thermostats, separator filtersTinvalve train bushing, wrist pin bushing, cam bushings, oil cooler core, thrust washers, governor, connecting rods bearings, valve gear train thrust buttons, journal bearing pads (babbit), bearings, separator filtersAluminiumengine blocks, pistons, blowers, oil pump bushings, bearings (some) cam bushings, oil coolers, pistons, aluminium complex grease contaminant, coolers, baffles, plates, housing, bearings, cylinder guides, wear plates, thrust washers, residue from synthetic media (alumina) filtersChromerings, liners, exhaust valves, zinc chromate from cooling system inhibitor, shaft coatings, some special gears are chrome plated, cylinder liners, cooler tubes, baffles, plates, bearings, cylinder guides, wear plates, thrust washers, bearings, oil pump, oil coolersLeadmain bearings, connecting rod bearings, red lead paint flakesSiliconengine blocks (alloying element with aluminium parts), ingested dirt from breathers, external sources, defoaming additive in lubricant, elastomeric seals, oil coolers, cooler tubes, baffles, plates, ingested dirt, silicone sealant, bearings, cooler (alloyed with aluminium)Silvervalves, valve guides, cylinder liners, bearings, heavy alloying element for tool steel gearsMetallic additivesSodiumcorrosion inhibitor additive, also indicates coolant leak into oil, can also be road salt, sea water, ingested dirtBoroncorrosion inhibitor additive, anti-wear/antioxidant additive, coolant leak, grease contaminationMagnesiumdetergent/dispersive additive, can also be alloying element in steelsCalciumdetergent/dispersant additive, alkaline reserve additive for high sulfur fuelled engines, can be grease contaminationMolybdenumsolid/liquid anti-wear additive, alloy in bearing and piston ringsBariumcorrosion inhibitors, detergents, rust inhibitorsZincanti-wear corrosion inhibitors, anti-oxidants, alloying element for bearings, thrust washers, galvanized casesPhosphorusanti-wear corrosion inhibitors, antioxidant additivesTitaniumwear metal for aircraft engines, bearings, paint (titanium dioxide)Vanadiumfuel contaminant, can also be alloying element for steel

1.9 Oils for New Generation Engines with Longer Drain Intervals

Oil is a part of the engine build like the connecting rod or the piston, unlike fuel and air which are consumables. The life of the oil is defined as the oil drain interval. The main driving force since 1990 for the development of API grades of oil is the concern over the environmental impact of diesel engine emissions. To further control emissions, lower limits on diesel fuel sulfur are set (reduction from 500 ppm sulfur to 15 ppm) (EPA, 2000). Demand for longer lasting oils as well as the concern over increased temperatures of the engine and oil sump due to current and future engine designs to meet these emissions standards have further driven the development of new engine oil service categories.

1.9.1 Engine Oil Developments and Trends

Selective catalytic reduction using ammonia from urea solution in conjunction with high pressure fuel injection enables achievement of very low nitric oxide and particulates levels along with the improved fuel efficiency by up to 10%. This technique is popular among most of the (truck, marine and electric power generation) engine designers in the world. Nevertheless, wary of handling urea solution, some engines are designed using a combination of cooled exhaust gas recirculation (EGR) at higher rates (30–35%) and exhaust after-treatment devices, such as catalytic diesel particulate filters and oxidation catalysts. There are some engines (Griffith, 2007) that use EGR gases drawn after the particulate filter and the clean gas does not induce engine wear. However, EGR engines commonly allow only unclean gases that cause wear. Therefore, the new generation of engine oils and diesel fuels are developed to provide durability of emission control systems, prevent catalyst poisoning and particulate filter blocking, while still offering optimum protection for control of piston deposits, oxidative thickening, oil consumption, high temperature stability, soot handling properties, foaming and viscosity loss due to shearing (Ludwig, 2007).

The diesel particulate filters are expected to operate for at least 240 000 km before they need cleaning. Engine emissions must comply for 696 000 km. The particulate filters are kept from clogging by active regeneration using electric or diesel heating or by passive regeneration using a catalyst (DECSE, 2000). The remaining residue and ash is blown against the exhaust flow and into a trap for disposal.

The new generation EGR engines generate more soot and experience higher peak cylinder temperatures due to the higher levels of EGR. This requires engine oil with improved oxidation resistance. A small amount of engine oil enters the combustion chamber and burns; its ash-like residue can lead to rubbing wear on the cylinder liner, causing the piston rings to not operate freely and, hence, higher oil consumption. In addition, metal oxide particles (ash) can be carried downstream with the exhaust to clog the diesel particulate filter.

In the exhaust stream, sulfur inhibits the effectiveness of the particulate filters by poisoning, and desensitizes the oxidation catalyst and the filter. It increases the conversion of sulfur oxides to sulfates, hence increases particulate emission and clogging of the filter. This can lead to reduced engine performance, due to increased backpressure and ultimately failure of the particulate trap.

Phosphorus in heavy duty diesel engine oils comes from the anti-wear agent zinc dithiophosphate (ZDP), corrosion inhibitors, friction modifiers and antioxidants. It can deactivate and damage the noble metal catalysts by coating on the active catalyst sites. As a result, harmful emissions, such as nitrogen oxides, carbon monoxide and hydrocarbons, increase.

To protect the after-treatment devices, the engine oil will have to contain lower sulfated ash, sulfur and phosphorus (SAPS), while still offering protection to the wear surfaces. SAPS are found in or derived from additives and base oils which help to extend oil drain intervals, base number (BN) retention, and protect against wear, oxidation, corrosion and piston deposits. However, lower sulfur in the new fuels is a blessing in disguise. Because of the use of ultra low sulfur diesel fuel in on-road applications, the metallic additives needed to maintain the required basicity (BN) of the oil will be correspondingly less, and thus the exhaust will have slightly lower ash content.

Considering all the points described above, API CJ-4 is developed to ensure protection of the after-treatment devices with chemical limits targeting the SAPS set for the first time ever for heavy duty diesel engine oils.

1.9.2 Shift in Engine Oil Technology

The low ash levels and the reduction in sulfur levels of the base oil and additives require replacing conventional metal-containing additives with alternatives low in metal content and sulfur, and in some cases ash-less. The use of these alternative additive chemistries has reduced the required basicity number from 10. For on-road diesel engines, this reduction in BN does not affect current oil life (drain interval) because of the use of ultra low sulfur diesel fuel (15 ppm maximum). Nonetheless, it can reduce oil drain intervals in diesel engines that will still be allowed to use 500 ppm sulfur fuels, for example, off road (Ludwig, 2007, Chapter 13).

The reduction in sulfur and volatility limits and the need for increased oxidation stability due to the increased thermal stress placed on the engine oil by the use of heavy EGR rates and after treatment resulted in an increased use of Group II, Group III and Group IV base stocks. The likely additional after-treatment devices, for example lean NOx catalysts, lean NOx traps, will further limit the chemistry of the oils to ensure compatibility of the catalyst and hence a number of severe tests are carried out to study the wear behaviour of critical parts (Whitcare, 2000) like cylinder liner, bearings, pistons and valve train.

1.10 Filters

Abrasive wear, pertaining to the internal combustion engine, has been the subject of numerous technical investigations, papers and articles. The majority of these presentations are in the area of filtration and the prevention of excessive or abnormal wear. Maintenance men must learn to determine if abrasive wear is present and then take corrective measures (Kolbe, 1969).

The contaminants from atmospheric air, combustion and degradation of oil are the most important in reducing the wear life of critical parts of a diesel engine. It is absolutely necessary to have improved filtration for air and oil filters to reduce engine wear (Fodor, 1979, 1982). The oil is operated by monitoring the contaminants within safe limits. Oil is one of the engine critical parts whose drain life must be very large. Therefore, filters play the most important role in maintaining the concentration of contaminants in the oil at a tolerable or economic level, as too large and fine a filter will be costly and unwieldy. The oil life is estimated when the acidity reaches the basicity or when the wear debris in the oil reaches set limits and the oil is ready for draining.

1.10.1 Air Filter

Airborne dust (quartz) is very abrasive and the most common cause of high wear of critical parts in engines. Studies have shown that engine life is a function of cleanliness of the air taken in (Sherburn, 1969). Concentrations and sizes of dust taken in by the engine determine wear life of an engine. Engine wear is produced by particles in the size range 1–40 μm and the most harmful particles are in the range 1–20 μm (Needleman and Madhavan, 1988; Treuhaft, 1993). Even in small amounts it can significantly increase the wear on piston rings and cylinder walls. By using high efficiency air and oil filters, engine wear can be significantly reduced (Jones and Eleftherakis, 1995). A part of the dust ingested by the engine eventually ends up in the oil. Silica in the oil should less than 25 ppm to limit its harmful effect. A new filter in modern engines has an efficiency of 99.8% and after about 20 000 km on the road this reaches 99.95%. In other words, the wear rate decreases fourfold, sometime after the new air filter element is placed.

1.10.2 Oil Filter

Similar to the air filter, the oil filter is a percentage filter, and hence a fraction of the dirt, soot and sludge inevitably passes through the filter to the bearing surfaces along with the oil. These particles initiate three-body wear and may result in seizure when caught in the small bearing gap but for the embeddability property of the overlay.

To enhance the wear life of the engine and the oil drain life, high capacity fine filters and bypass filters are helpful. A filter is considered nominally efficient at a certain micron level if it can remove 50% of particles of that size. In other words, a filter that will consistently remove 50% of particles 20 microns or larger is nominally efficient at 20 microns. Three times the reduction in the contaminants could be observed by using a ten micron bypass filter in conjunction with a main filter rated at 40 micron (Land, Shadday and Philips, 1979). Abrasive engine wear can be substantially reduced with an increase in filter efficiency. Compared to a 40 micron filter, engine wear was reduced by 50% with 30 micron filtration. Likewise, wear was reduced by 70% with 15 micron filtration (Staley, 1988). A filter is considered to achieve absolute filtration efficiency at a certain micron level if it can remove 98.7% of particles that size. Today, it is usual to have a 15–20 micron full flow filter with a tighter bypass filter. It was also reported by Staley (1988) that for the same oil quality, the wear of the main bearing was proportional to the contaminants and that improving the filtering improved the wear rate of main and connecting rod bearings by better than 95% and of the piston ring wear rate by 90%. In other words, if the contaminants are completely eliminated from the oil, the wear life of engine parts would enhance substantially.

1.10.3 Water Filter

Scale is formed in the coolant circuit and also there is precipitation of hard salts in the water. These are abrasive and wear out the seal in the water pump. Also, where the velocity of water flow is less and the passages are narrow, build up of debris could obstruct the coolant flow and cause heating up of the engine and oil film locally. Boundary lubrication related wear could be the consequence. A bypass filter in the water circuit solves these problems satisfactorily.

1.10.4 Fuel Filter

Advanced emission norms require higher injection pressures. However, higher injection pressures are obtained with very tight clearances between the metallic parts in the fuel injection pump and the injector so that the leakage through the clearances is kept low, even at higher fuel pressures. Correspondingly, the demand on the fuel filters for higher efficiency to limit small particles is high.

1.11 Types of Wear of Critical Parts in a Highly Loaded Diesel Engine

The book focuses on the life of the critical parts namely liner, piston, piston rings, bearings and components in the valve train affected by the adhesive, abrasive, corrosive and fretting wear.

1.11.1 Adhesive Wear

This form of wear occurs when two smooth bodies slide over each other or one surface adheres to the other. The strong adhesive forces arise out of intimate interaction at molecular level. In this process, the wear particles are pulled off from the softer surface and become welded to the harder surface. For example, cylinder bores will wear at the top ring reversal zone due to the adhesive action of piston rings under gaseous load.

1.11.2 Abrasive Wear

Abrasive wear occurs when a rough surface slides against hard particles, causing a series of scratches on the smoother surface, and the material from the softer surface is displaced in the form of wear particles. For example, a diesel engine running on heavy furnace oil undergoes wear of the piston grooves due to abrasive action of hard carbon particles produced by combustion.

1.11.3 Fretting Wear

Fretting wear arises when contacting surfaces undergo oscillatory tangential displacement of small amplitude. It is a type of wear because of the cyclic motion that produces a displacement (under high contact pressure) that is so small that it may be difficult to anticipate a large volume of wear debris. The wear of the inlet valve seat due to micron-scale displacement under highly loaded conditions illustrates fretting mode of wear in diesel engines.

1.11.4 Corrosive Wear

Virtually all materials except noble metals like gold or platinum corrode in the normal environment. The most common form of corrosion is oxidation. Most metals react with oxygen in air or water to form oxides. Abusive conditions, for example low or high temperatures, increase the rate of chemical reactions and the corrosive wear increases abruptly, leading to mechanical destruction of the surface layer due to sliding or rolling contact of two mating bodies. Typically, the greyish lapped appearance of liner surfaces under cold running condition is an example of corrosive wear.

References

Archard, J.F. and Hirst, W. (1956) The Wear of Metals under Unlubricated Conditions. Proceedings of the Royal Society London, A, 236, 397–410.

Bentley Tribology Services (2010) Sources of Wear Metals in Oil Analysis. http://www.bentlytribology.com/publications/appnotes/app31.php (accessed 20 May 2011).

DECSE (2000) Phase 1 Interim Report No. 4: Diesel Particulate Filters – Final Report. Diesel Emission Control – Sulfur Effects (DECSE) Program, US Department of Energy/Engine Manufacturers Association/Manufacturers of Emission Controls Association, USA.

EPA (2000) Regulatory Impact Analysis: Heavy-duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements. EPA 420-R-00-26, Assessment and Standards Division, Office of Transportation and Air Quality, United States Environmental Protection Agency, Washington, DC, pp. 96–98.

Fodor, J. (1979) Improving Utilization of Potential I.C. Engine Life by Filtration. Tribology International, 12, 127–129.

Fodor, J. (1982) Improving the Economy of I.C. Engines by Controlling the Contaminants Through Filtration. World Filtration Congress III, Downingtown, PA, pp. 707–711.

Griffith, R.C. (2007) Series Turbocharging for the Caterpillar® Heavy-Duty On-Highway Truck Engines with ACERT™ Technology. Technical Paper 2007-01-1561, SAE, Troy, MI.

Heywood, J. B. (1988) Internal combustion engine fundamentals. McGraw-Hill, p. 669.

Jones, G.W. and Eleftherakis, J.G. (1995) Correlating Engine Wear with Filter Multipass Testing. Fuels & Lubricants Meeting and Exposition, 16–19 October 1995, Toronto, Canada, Technical Paper 952555, SAE, Troy, MI.

Kolbe, J. F. (1969) Abrasive Wear – Identifications and Prevention. Technical Paper 690544, SAE, Troy, MI.

Land, O.H., Shadday, P.D. and Philips M.C. (1979) Diesel Engine Wear with Spin on – bypass lube oil filters. Technical Paper 790089, SAE, Troy, MI.

Ludwig, L.G. (2007) Heavy-duty Diesel Engine Oil Developments and Trends. Machinery Lubrication.http://www.machinerylubrication.com/Read/1036/diesel-engine-oil (accessed 20 May 2011).

Needleman, W.M. and Madhavan, P.V. (1998) Review of Lubricant Contamination and Diesel Engine Wear. Truck and Bus Meeting and Exposition, 7–10 November 1998, Indianapolis, IN, Technical Paper 881827, SAE, Troy, MI.

Sam, G., Balla, S. and Gautam, M. (2007) Effect of diesel soot contaminated oil on engine wear. Elsevier Science, Vol. 262 (9–10), pp. 1113–1122.

Sherburn, P.E. (1969) Air Cleaner Design – Present and Future. International Automotive Engineering Congress, 13–17 January 1969, Detroit, MI, SAE Technical Paper 690007.

Staley, D.R. (1988) Correlating Lube Oil Filtration Efficiencies with Engine Wear. Technical Paper 881825, SAE, Troy, MI.

Totten, G.E., Westbrook, S.R. and Shah, R. J. (2003) Fuels and lubricants handbook: technology, properties, performance, Vol. 1. ASTM International, West Conshohocken, PA.

Treuhaft, M.B. (1993) The Use of Radioactive Tracer Technology to Measure Engine Ring Wear in Response to Dust Ingestion. International Congress and Exposition, 1–5 March 1993, Detroit, MI, Technical Paper 930019, SAE, Troy, MI.

Whitcare, S. (2000) Catalyst Compatible Diesel Engine Oils, DECSE Phase II. Presentation at DOE/NREL Workshop Exploring Low Emission Diesel Engine Oils, 31 January–2 February 2000, Phoenix, AZ.

Chapter 2

Engine Size and Life

Parameters like brake mean effective pressure, mean velocity of the piston, surface hardness, oil film thickness and surface areas of critical wear parts are similar for all the diesel engines. The mean piston velocity at the rated speed is nearly the same for all diesel engines. The mechanical efficiency normalized to an arbitrary brake mean effective pressure (bmep) is dependent on the size of the engine. The engine life seems to be proportional directly to the square of a characteristic dimension of the engine and inversely to speed and load factor for engines varying widely in sizes and ratings.