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dieselenginebasics

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dieselenginebasics

Simpson and Stephen Murray


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Copyright © 2012 McGraw-Hill Australia Pty LimitedAdditional owners of copyright are acknowledged on the acknowledgments page

Every effort has been made to trace and acknowledge copyrighted material. The authors and publishers tender their apologies should any infringement have occurred.

Reproduction and communication for educational purposesThe Australian Copyright Act 1968 (the Act) allows a maximum of one chapter or 10% of the pages of this work, whichever is the greater, to be reproduced and/or communicated by any educational institution for its educational purposes provided that the institution (or the body that administers it) has sent a Statutory Educational notice to Copyright Agency Limited (CAL) and been granted a licence. For details of statutory educational and other copyright licences contact: Copyright Agency Limited, Level 15, 233 Castlereagh Street, Sydney NSW 2000. Telephone: (02) 9394 7600. Website: www.copyright.com.au

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Enquiries should be made to the publisher via www.mcgraw-hill.com.au or marked for the attention of the permissions editor at the address below.

National Library of Australia Cataloguing-in-Publication DataAuthor: Simpson, Les.Title: Diesel engine basics / Les Simpson, Stephen Murray.ISBN: 9781743071519 (pbk.)Notes: Includes index.Subjects: Diesel motor—Maintenance and repair.

Motor vehicles—Maintenance and repair.Other Authors/Contributors: Murray, Stephen.Dewey Number: 621.4368

Published in Australia byMcGraw-Hill Australia Pty LtdLevel 2, 82 Waterloo Road, North Ryde NSW 2113Publisher: Norma Angeloni-TomarasEditorial coordinator: Carolina PomilioSenior production editor: Claire LinsdellPermissions editor: Haidi BernhardtCopyeditor: Kathryn FairfaxProofreader: Nicole McKenzieIndexer: Olive Grove IndexingCover and internal design: Jane CameronTypeset in Minion Pro Regular 10.5/13pt by diacriTech, IndiaPrinted in China on 80 gsm matt art by R R Donnelly


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contents in brief

CHAPTER 1 Diesel Engine Terminology 1

CHAPTER 2 Engine Construction 9

CHAPTER 3 Fuels and Lubricants 23

CHAPTER 4 Fuel Supply Systems 35

CHAPTER 5 In-line and Single Element Pumps 45

CHAPTER 6 Distributor Pumps 53

CHAPTER 7 Unit Injection 65

CHAPTER 8 Common Rail Diesel 75

CHAPTER 9 Hydraulic Injection 87

CHAPTER 10 Governors 95

CHAPTER 11 Intake and Exhaust Systems 103

CHAPTER 12 Cooling Systems 113

CHAPTER 13 Starting and Charging Systems 125

CHAPTER 14 Diagnosis and Maintenance 131


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About the authors ixPreface xAcknowledgments xiCompetency grid xiiOLC page xiii

CHAPTER 1 DIESEL ENGINE TERMINOLOGY 1

Introduction 2Engine terminology 2Operating cycles 3Combustion process 4Technical terms 7Questions 7

CHAPTER 2 ENGINE CONSTRUCTION 9

Cylinder blocks 10Cylinder sleeves 10Crankshafts 11Balance shafts 11Bearings 12Connecting rods 12Pistons 12Piston rings 13Cylinder heads 13Combustion chambers 14Engine valves 16Camshafts 16Valve timing 18Two-stroke timing 19The valve train 20Technical terms 21Questions 21

CHAPTER 3 FUELS AND LUBRICANTS 23

Introduction 24Biodiesel 24

Diesel fuel properties 24Clean diesel fuel 25Diesel engine lubrication 25Lubricating oil classifications 26Lubricating systems 27Engine lubrication oil pumps 29Oil filters 31Oil coolers 32Technical terms 34Questions 34

CHAPTER 4 FUEL SUPPLY SYSTEMS 35

Introduction 36Diesel fuel storage tanks 36Low pressure/lift pumps 36Fuel filters 40Hoses and pipes 42Technical terms 42Questions 43

CHAPTER 5 IN-LINE AND SINGLE ELEMENT PUMPS 45

Introduction 46In-line pump and single element construction 46In-line pump operation 46Single element operation 47In-line injection pump fitting and timing 48Injection pump servicing 50Technical terms 51Questions 51

CHAPTER 6 DISTRIBUTOR PUMPS 53

Introduction 54Axial-type distributor pump 54Radial-type distributor pump 57Distributor injection pump fitting and timing 59


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Electronic diesel control 62Technical terms 63Questions 63

CHAPTER 7 UNIT INJECTION 65

Introduction 66Mechanical unit injector (MUI) types and operation 66Hydraulically actuated electronically controlled unit injectors (HEUI) operation (Caterpillar, GM, Ford) 69Electrically controlled unit injector 71Fuel injector calibration 73Technical terms 73Questions 73

CHAPTER 8 COMMON RAIL DIESEL 75

Introduction 76Basic components of a common rail diesel system 76CRD system operation 76Operating processes and control system 77Common rail diesel low-pressure system 78Common rail diesel high-pressure system 79CRD emission systems and control 82Engine oil and filter replacement 84Technical terms 85Questions 85

CHAPTER 9 HYDRAULIC INJECTION 87

Introduction 88Hydraulic injectors 88Injector servicing 91

Technical terms 93Questions 93

CHAPTER 10 GOVERNORS 95

Introduction 96Types of governors 96Governor terminology 96Governor operation 96Mechanical governors 97Hydraulic governors 98Pneumatic governors 98Additional governor features 99Electronic governors 99Technical terms 101Questions 101

CHAPTER 11 INTAKE AND EXHAUST SYSTEMS 103

Introduction 104Intake systems 104Air charge cooling 106Two-stroke engine blower 108Exhaust systems 108Technical terms 112Questions 112

CHAPTER 12 COOLING SYSTEMS 113

Introduction 114Heat and temperature 114Heat transfer 114Types of cooling systems 114Liquid cooling systems 114Pressurised cooling systems 115Coolant 116Fans and fan drives 118


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Marine cooling systems 122Air cooling 122Technical terms 123Questions 123

CHAPTER 13 STARTING AND CHARGING SYSTEMS 125

Introduction 126Types of starting systems 126Starting assistance 128Charging systems 129

Technical terms 130Questions 130

CHAPTER 14 DIAGNOSIS AND MAINTENANCE 131

Introduction 132Diagnosis 132Maintenance 136Technical terms 136Questions 136


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ABOUT THE AUTHORS IX

LES SIMPSON

Les has more than 30 years’ teaching experience and currently teaches at the Sydney Institute of TAFE. Les is a member of the Institute of Automotive Mechanical Engineers and holds a Diploma in Teaching (Technical) and a Certificate IV in Automotive Technology. During his career he has taught trade and farm mechanics, plant and heavy equipment, and light vehicle mechanics at both country and metropolitan colleges.

Les has worked overseas for TAFE NSW assisting the governments of Malaysia and the People’s Republic of China to deliver vocational education and training (VET) pro-grams. Prior to joining TAFE NSW, Les served as a member of the Australian Army and it was during his army career that he completed his apprenticeship and gained valuable experience working on a variety of vehicles and equipment.

Les is a keen supporter of WorldSkills Australia as a both national judge and Sydney regional organiser.

STEPHEN MURRAY

Stephen has over 40 years’ experience in the automotive industry. He started his career in the Australian Army where he gained a vehicle mechanic qualification and worked as a mechanic. After leaving the Army, Stephen went on to become a vehicle technician and workshop owner and operator, and this led to his involvement in service management and training.

Stephen holds a Certificate IV in Training and Assessment and has been a member of the Institute of Automotive Mechanical Engineers for 30 years. He has worked on armoured vehicles, earthmoving equipment, trucks of various sizes and light vehicles with electrical, mechanical, petrol, diesel and hydraulics systems.

Stephen’s passion in life is training and he has a particular interest in the research, development and delivery of training for dealerships and aftermarket workshops. He has been providing training for technicians and apprentices within the automotive industry for 25 years, helping technicians keep their technical knowledge up-to-date and ensuring that they are competent to operate in today’s very challenging environment.

Stephen and Les have known each other since their days in the Australian Army.


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X DIESEL ENGINE BASICS

The purpose of this book is to give the reader an overview of the operation of the diesel engine and its ancillary systems. It covers light vehicle, heavy vehicle, off-road and marine basic diesel principles. All of the major types of fuel systems are explained in easy-to-understand language and are supported by illustrations, graphs and pictures. The text also contains maintenance and diagnosis procedures.

DisclaimerThe authors have not included the repair and overhaul of systems or components because it is not the purpose of this text. Specialist equipment and workshop facilities are required to carry out most overhaul procedures on diesel systems. Any specifications or procedures stated in this text are meant to be a guide only. The appropriate workshop manual should always be consulted before any repairs are attempted.


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ACKNOWLEDGMENTS XI

AudiBMWCaterpillar AustraliaCummins Diesel AustraliaDaihatsu AustraliaDeutzDonaldson Filtration solutionsLuxfords Marine Industrial

OpalRobert Bosch (Australia) Pty LtdRover Australia Pty LtdTDI Air StartersToyota AustraliaTridon AustraliaZexel Corporation Australia

The authors would like to thank the following organisations for providing technical information and their kind permission to use illustrations.

The authors would also like to thank Ed May for allowing the use of text and illustra-tions from Diesel Mechanics.


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XII DIESEL ENGINE BASICS

Diesel Engine Basics contains materials that relate to national competency standards in the Australian National Training Package AUR05v3.0

Competency Reference Description Text reference

AURT200108A Carry out servicing operations Chapter 3,4,9,14

AURT366108A Carry out diagnostic procedures Chapter 14

AURT201170A Inspect and service engines Chapter 1,2,3,4

AURT203670B Service Diesel fuel systems Chapter 1,2,3,4,5,6,7,8,9,10,11,14

AURT303666A Repair Diesel fuel systems Chapter 1,2,3,4,5,6,7,8,9,10,11,14

AURT202170B Inspect and service cooling systems Chapter 1,2,12


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OLC PAGE XIII

DIGITAL RESOURCES: STUDENT

OLCThe Online Learning Centre (OLC) that accom-panies this text helps you get the most from your course. It provides a powerful learning experi-ence beyond the printed page.

www.mhhe.com/au/dieselbasics

Student revision toolStudents can test their knowledge of key con-cepts using our online quizzes. Each chapter has a set of multiple choice questions designed for self-paced revision. Answers to the questions are supplied along with references to the relevant sections in the book.

DIGITAL RESOURCES: INSTRUCTOR

In addition to all student resources, instructors have additional password-protected access to:

Facilitator guideThe Facilitator guide provides the instructor with a chapter-by-chapter summary of the text, solutions to all end-of-chapters questions, and additional teaching resources to enhance students’ learning.

Artwork libraryIllustrations and tables from the text are available in an online artwork library as digital image files. Instructors thus have the flexibility to use them in the format that best suits their needs.

DIGITAL RESOURCES: EBOOKTo assist in flexible learning, Diesel Engine Basics is available in print and eBook formats. Our eBooks enhance students’ learning experience and assist with blended and e-learning strategies. Enjoy the convenience of accessing the eBook via computer, laptop or tablet, as well as interacting with the highlighting, note taking and search engine functionalities.


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� In-line pump and single element construction

� In-line pump operation

� Single element operation

� In-line injection pump fitting and timing

� Injection pump servicing

Technical termsQuestions

in-line and single element pumps

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46 diesel engine basics

In-lIne and sIngle element pumps

ObjectIveThe objective of this chapter is to gain knowledge of the inline diesel fuel injection pump, its basic operation and servicing requirements.

Injectionpipe Injector Filters

Controllever

GovernorFuel supplypump

Automaticadvancedevice

FIgure 5.1 An in-line injection pump and associated components on an engine

IntrOductIOn

A basic in-line injection pump has separate pumping elements, one for each cylinder of the engine. Each pumping element is operated by a cam on the pump camshaft. Because the pump supplies the injectors with fuel in short jerks, it is sometimes referred to as a jerk-type pump. The pump’s camshaft is connected to an auxiliary shaft on the engine, which is driven by the timing gears. The coupling connects the auxiliary shaft to the pump’s camshaft and also allows the pump to be timed to the engine. With the engine running, the pump will rotate at half engine speed for a four-stroke engine.

advantages and disadvantages

Table 5.1 Advantages and disadvantages of an in-line injection pump

advantages Disadvantages

better suited for larger engines with low speed operation

Heavy

Reliable noisy

Requires phasing, calibrating and timing

Examples of a full in-line pump system and components are shown in Figures 5.1 and 5.2.

In-lIne pump and sIngle element cOnstructIOn

The internal operating components can be divided into the following groups:

• Main pumping componentsCamshaft, tappet, plunger, barrel and delivery valve.

• Control componentsControl rack, control sleeve and plunger control arm.

• Fuel componentsFuel gallery, supply pump, hand priming pump and injector pipes.

In-lIne pump OperatIOn

The supply pump of the fuel system keeps the gallery of the injection pump full of fuel for the pumping ele-ments. As the camshaft rotates, the cam lifts the tappet of one of the pumping elements. This raises the plunger in its barrel and fuel is delivered from the delivery valve at the top of the pump to an injector. After the plunger has completed its upward stroke, it moves downwards under the action of the spring, which holds the roller against the cam.

The four plungers of the pumping elements oper-ate in the same way. They are accurately phased so that a plunger delivers fuel at each 90° of pump rotation


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chapTer 5 in-line and single element pumps 47

(four-cylinder engine). The control rod is used to vary the quantity of fuel delivered by the injection pump. When the rod is pushed in, more fuel is delivered by the pumping elements, and vice versa. When the rod is pushed right in, the pump delivers maximum fuel for maximum engine power. When the rod is pulled right out, the fuel supply to the injectors is cut off and the engine is stopped.

sIngle element OperatIOn

The cam of the camshaft raises the tappet and this lifts the plunger in its barrel. Fuel from the gallery enters the barrel through the inlet port and delivery com-mences. Fuel trapped in the barrel is pumped through the delivery valve to the injector. After completing its stroke, the plunger follows the cam downwards to complete the cycle. The plunger does not always pump the same quantity of fuel. This is controlled by the con-trol rod or rack. The teeth of the rod mesh with the teeth on the control sleeve. Moving the rod rotates the sleeve and alters the position of the plunger in its bar-rel. This alters the quantity of fuel that is pumped by the plunger. The plunger always travels through its full stroke, but does not always pump a full stroke of fuel (see Figures 5.3 and 5.4).

Delivery valve

Control rod

Barrel

Plunger

Coupling

TappetCamshaft

Spring

Fuelgallery

Stop

Inlet port

Pumping chamber

FIgure 5.2 Basic in-line injection pump

Fuel-injection tubing

Fuel gallery

Barrel

PlungerControl sleevegearControl rack

Control sleevePlunger control arm

Plunger returnspringSpring seat

Roller tappet

Camshaft

Cam

Supply pump

Adjusting screw with nut

Delivery valve

FIgure 5.3 Section through an in-line injection pump


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effective plunger stroke

The control rod is used to control fuel delivery. Its teeth are meshed with a gear segment that is clamped to the control sleeve. When the sleeve is turned, the plunger is turned in its barrel.

Delivery valveholder

Spring

Delivery valve

Barrel

Fuel gallery

Pumphousing

Control rod(rack)

Control sleeve

Spring

Tappet

Camshaft

Plunger

Gear segment

FIgure 5.4 The pumping parts of one element of an in-line injection pump

The barrel has two opposite ports: an inlet port and a spill port. These are aligned with the fuel gallery so that fuel fills the barrel when the plunger is at the bottom of its stroke. The plunger is not just a plain rod; it has a specially shaped groove that forms a helix on the plunger. The effec-tive pumping stroke occurs when the top of the plunger covers the inlet port, until the helix uncovers the spill port.

Figure 5.5 shows the effective stroke of the plunger in three different positions: no delivery, partial delivery and maximum delivery.

• No deliveryThe plunger has moved up the barrel and covered the inlet port, but the helix has not covered the spill port (see Figure 5.5(a)). Fuel will flow back to the gallery and there will be no delivery.

• Partial deliveryThe control rod has turned the sleeve and the plunger so that the helix covers the spill port (see Figure 5.5(b)). As the plunger rises, delivery will take place until the edge of the helix uncovers the spill port. Fuel will spill from the barrel and delivery will cease.

• Maximum deliveryThe rack has been moved to its maximum position, and the sleeve has turned the barrel further than before (see Figure 5.5(c)). The plunger starts delivery at the same place, but it lasts longer. This is because of the shape of the helix—the plunger now has to travel further up the barrel before the helix uncovers the spill port.

In-lIne InjectIOn pump fIttIng and tImIng

In-line injection pumps may have two timing marks, one on the engine and one on the injection pump. The tim-ing mark on the engine may be located on the vibration

FIgure 5.5 Control rod or rack used to alter the effective pump stroke to control fuel delivery

Pump barrel

Inletport Spill

port

Effective stroke

Helix

Control rod

(C) Maximum delivery(b) Partial delivery(a) No delivery

Pump plunger


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damper, on the pump coupling or on the flywheel. If it is necessary to remove the pump and there are no tim-ing marks, try to mark corresponding spots on the pump and engine before removing the pump.

The following are general points that relate to install-ing an injection pump:

• The engine is set on the timing mark, with No. 1 piston on the compression stroke. This is the point where injection should commence.

• The injection pump is set in the position where it is just starting to pump fuel to the injector in No. 1 cylinder. This position is identified by a mark or pointer on the pump and a corresponding mark on the pump coupling.

• With both the engine and the pump set to their correct injection positions, the pump is installed on the engine. The timing marks are checked and an adjustment made if necessary.

The general procedure for injection pump timing has been outlined above, but the actual procedure will vary with different engines and with different pumps.

For examples of timing marks for an in-line pump, see Figure 5.6. The pump in Figure 5.6(a) has an open type of coupling which enables the timing marks to be readily identified. The pump in Figure 5.6(b) is flange-mounted to the rear of the timing case. There is a timing mark on the pump flange and a corresponding mark on the timing case. The pump coupling is inside the timing case. This also carries a timing mark that is aligned with a pointer on the timing case. These two marks are accessible through an aperture in the timing case after a small cover is removed.

spill timing

If an in-line injection pump has no timing marks, or if these need to be verified, the point at which injection commences can be found by spill timing. This point is where the plunger, moving upwards in its barrel, closes off the fuel inlet port. When the inlet port closes, injection is about to commence.

The procedure for spill timing is as follows:1. Set the engine with No. 1 cylinder on compression

stroke, with the engine timing mark in line with the pointer.

2. Disconnect the injector pipe for No. 1 cylinder from the delivery valve on top of the pump. Unscrew the delivery valve holder and remove its valve, spring, etc.

3. Remove the delivery valve holder and attach a ‘gooseneck’ spill pipe to it (see Figure 5.7).

4. Operate the priming pump to obtain a continuous flow of fuel from the spill pipe. If there is no flow, rotate the pump a little.

5. With the injection pump drive coupling loose, turn the injection pump flange slowly in the direction of rotation. The plunger of the pump element will rise on its pumping stroke.

6. Turn the pump very slowly and carefully observe the flow of fuel from the spill pipe. As the plunger rises in its barrel, the fuel from the spill pipe will decrease to a drip. When the inlet port becomes fully closed, the fuel will cut off completely. This point is referred to as spill cut-off. It is when there is no drip from the spill pipe for a period of about 15 seconds.

7. Secure the pump drive coupling in this position, with the engine on its timing mark and the injection pump at spill cut-off position.

8. Remove the spill pipe, replace the parts in the delivery valve holder and reconnect the injector pipe.Ensure the delivery valve holder and pipes are thor-

oughly cleaned prior to refitting and torque to manu-facturer’s specification. If the fuel supply to the pump

Mark

(a)

(b)

Mark

MarkMarks

Pointer

FIgure 5.6 In-line injection pump timing marks:(a) marks on coupling and pump,(b) marks on coupling, timing case and pump


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has been disconnected or a new pump used, the pump will have to be primed and bled before commencing the procedure.

InjectIOn pump servIcIng

Any work that has to be carried out on injection pumps that goes beyond removal and replacement or on-the-vehicle adjustments requires special facilities. These include an air-conditioned room, an injection pump testing machine and special tools. Also required for each model of pump are specifications and data related to pump adjustments, torque settings of bolts and screws and performance figures for testing purposes.

Injection pump overhaul is outside the normal scope of a mechanic’s work. However, some idea of the general procedures that are carried out during pump overhaul is desirable and the following paragraphs are intended to provide only that. They do not describe overhaul pro-cedures. Apart from specialised equipment, injection pump work also calls for cleanliness, accuracy and atten-tion to detail.

The attention to detail for emission level require-ments and manufacturers’ specifications also extends to the warranty on new, serviced or overhauled pumps. New, serviced and overhauled pumps are a sealed unit. Any adjusting device will be sealed. Any attempt to alter the original settings will render the pump outside any emission requirements and void any warranty on the pump.

pump overhaul

When an injection pump is removed from an engine, it can be set up on a test bench to check its condition or to locate faults. Repairs or adjustments are then made on the basis of the test results.

An injection pump consists of a large number of fairly small parts, which are separated during disman-tling. The parts should be subjected to a visual inspec-tion and identified as they are being dismantled. All dismantled components need to be closely inspected. Any component that shows signs of fretting, damage, wear, corrosion, cracks or distortion should be discarded and replaced with a new part. During pump overhaul, all O-rings, seals, gaskets, tab washers and locking devices that are removed must be replaced.

pump testing

Testing machines have a variable-speed electric motor to drive the pump and a bracket on the bed of the machine on which the pump is mounted. The test bench has a set of matched injectors that are operated by the pump and graduated test tubes to collect and measure the fuel from the injectors. There are also various instruments, includ-ing pressure gauges and a tachometer. In addition, some test benches have electronic measuring equipment.

Injection pumps can be tested for:

• pump output• maximum fuel setting• governor action• feed pump operation and pressure setting• timing advance device operation.

The internal timing of the pump is also checked and adjusted in relation to the timing mark on the flange of the pump housing.

In addition to the other bench tests, in-line pumps must be phased and calibrated as part of the overhaul and test procedure. This is done to ensure that all the pumping elements are operating correctly in relation to each other.

phasing

This is the procedure of checking and adjusting the intervals (phase angle) between successive injections. For example, the injection pump for a four-cylinder engine has a phase angle of 90° and a six-cylinder engine has a phase angle of 60°. The testing machine has a degree plate. Using spill cut-off of No. 1 cylinder pump element as a basis, the spill cut-off for the other cylinders is checked in firing order. These should be evenly spaced during 360° of pump rotation. Adjustment of the phase

Parts removed

Spill timing pipeDeliveryvalve holder

Pump coupling

FIgure 5.7 Spill timing an in-line injection pump. The delivery valve, spring and volume reducer are shown in inset


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angle can be made by changing the tappet spacers inside the pump or, in some pumps, by adjusting the tappet screws. This causes the plunger action to start earlier or later as required to correct the phase angle.

calibrating

The pump is tested and, if necessary, calibrated (adjusted) so that the same volume of fuel is delivered from each pumping element. This ensures that all the cylinders will produce equal power. Adjustments are made by altering the positions of the gear segments on the sleeves. Loosening the clamp and adjusting the gear segment turns the plunger in its barrel and this alters the quantity of fuel that it delivers.

The injection pump is mounted on the test bench and is then run at speeds listed in the specific data for the particular pump. The amount of test oil delivered into the calibrated test tubes is then checked for a speci-fied number of shots (e.g. 200). All pumping elements should deliver the same volume during the testing period. This can be checked by comparing the level of oil in the graduated test tubes. Where there is electronic measuring equipment, information will be displayed.

Questions

1. What checks should be made before removing an injection pump?

2. name at least four main pumping components of an in-line pump.

3. What is the rotating speed of an in-line pump fitted to a four-cylinder four-stroke engine running at 2500 rpm?

a. 1250

b. 2000

c. 4000

4. What lifts the plunger in the barrel of a single element?

5. using Figure 5.4, explain the operation of the control rod.

6. using Figure 5.5, explain the effective stroke of the plunger in the three different positions.

7. What is spill timing?

8. explain briefly how spill timing is carried out.

9. What is the purpose of an injection pump testing machine?

10. What is meant by the phasing of an in-line injection pump?

11. explain calibrating in relation to an in-line pump.

12. injection pumps can be tested for:

a. pump output and maximum fuel setting

b. governor action

c. feed pump operation and pressure setting

d. timing advance device operation

e. all of the above.

13. How are the internal components lubricated?

14. name at least three pump control compo-nents of an in-line pump.

15. What may occur if an injector pump is not timed correctly?

Technical terms

• calibrating

• camshaft

• degree

• firing order

• fretting

• gallery

• in-line

• phase angle

• phasing

• pumping element

• specifications

• spill cut-off

• spill pipe

• spill timing

• tappet

• timing mark

• tube


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hydraulic injection� Hydraulic injectors� Injector servicing

Technical termsQuestions


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Hydraulic injection

objectiveThe objective of this chapter is to gain knowl-edge of hydraulic injector operation, the dif-ferent types of injectors and minor servicing.

introduction

Chapters 7 and 8 provided information about diesel injectors that were controlled mechanically, electrically and a combination of these with hydraulic fuel pressure. This chapter will cover the base fuel hydraulically oper-ated injector, which is the main type of injector that has been used for many years in all types of diesel engines, from marine and automotive to small stationary engines. These injectors are still used on many engines; however, the new electrically controlled systems will eventually become more commonly used.

Hydraulic injectors

Hydraulic injectors come in various shapes and sizes. They can be either threaded like a spark plug and screwed into the cylinder head, held in place by a clamp, or they may have a flange built into the body that is bolted to the cylin-der head. The nozzle at the lower end of the injector either fits against the combustion chamber or projects slightly into it. At the appropriate time, the nozzle directs a fine spray of fuel into the combustion chamber. See Figures 9.1 to 9.4 for examples of injectors and components.

injector operation

The fuel inlet and outlet return connections on the injec-tor are usually located on the top or side of the injector. The main operating components are the:

• needle• spindle• spring. FIgure 9.2 Flanged-type injector

Cap nut

Fuel inlet

Nozzle holder

Nozzle nut

Nozzle

Fuel inlet

Fuel-return outlet

Body

Spring

Nozzle holder

Needle valve

Nozzle

Pressure chamber

FIgure 9.1 Sectional view of threaded injector


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cHapter 9 Hydraulic injection 89

Spring force is transferred through the spindle to the needle. This holds the needle on its seat and prevents fuel from leaking out the end of the nozzle. With the engine stopped the injector holds fuel, but it is not under pressure.

The controlled delivery of fuel from the injection pump enters the injector through the inlet connection. It passes down the drilled passage to the gallery in the nozzle near the bottom of the injector. When the gallery is pressurised with fuel, the needle is forced upwards against the spring. With the needle tip off the nozzle holes, the high-pressure fuel in the gallery is sprayed into the combustion chamber. When delivery from the injection pump ceases, the pressure in the injector drops and the spring returns the needle to its seat (see Figure 9.5).

It is the speed at which the pressure in the injector drops that causes the needle to close rapidly. This ensures complete sealing between the needle tip and the nozzle holes. Any fuel that leaks or dribbles into the combus-tion chamber will not burn properly and may cause soot or black smoke from the exhaust.

Body

Shim

Spring

Rod

Needle

Nozzle

Nozzleholder

Spacer

FIgure 9.4 Dismantled parts of an injector

Spring

Spindle

Needle

Gallery

Nozzle

Fuelpassage

Fuelinlet

FIgure 9.5 Simplified diagram showing injector action

Leak-offconnection

Spring

Spindle

Nozzlenut

Nozzle

Nozzle holder

Adaptor

Adjustingnut

Cap nut

FIgure 9.3 Internal construction of a flanged-type injector


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The fine holes in some injector nozzles are drilled mechanically. In others, the holes are so small they require a process called electrical discharge machining. The diam-eter of the hole can be as small as 0.2 mm (see Figure 9.6).

types of nozzles• Single hole nozzles

These nozzles have a single small hole drilled through the nozzle end. The conical end single-hole nozzle has a single hole drilled at an angle to suit the particular engine design.

• Multi hole nozzlesThese nozzles have two or more holes drilled in the end of the nozzle. The number of holes and their size and position depend on the requirements of the engine.

• Long stem nozzlesThese nozzles have a long stem that is an extension of the underside of the nozzle. The end of the stem carries the normal holes and valve seat. The long stem enables the part of the nozzle that has fine clearances (between the needle and the nozzle) to be kept away from the combustion chamber. This enables this part of the injector to operate in a comparatively cooler area of the cylinder head.

• Pintle nozzlesThese nozzles have a much larger hole than other types. The end of the needle is formed into a pin or pintle that protrudes through the hole. By modifying the shape and size of the pintle, injectors can produce different spray patterns. The spray can be varied from a small hollow cone to a hollow cone with an angle of 60°s. Delay nozzles are a modified pintle type in which the shape of the pintle has been designed to reduce the rate of injection at the beginning of the delivery. This decreases the amount of fuel in the combustion chamber when combustion commences, to assist in the control and reduction of diesel knock. Pintle nozzles are designed for use in engines with indirect injection and engines with an air cell, a swirl chamber or a pre-combustion chamber (see Chapter 2).

• Sac-hole and seat-hole nozzlesSome nozzles have a small chamber under the tip of the needle into which the holes are drilled. This is called a sac-hole and the nozzles are referred to as sac-hole nozzles. Other nozzles have their holes drilled into the nozzle seat and are referred to as seat-hole nozzles. With seat-hole nozzles, the taper on the needle tip covers the hole and so the needle is not exposed to the combustion gases. (see Figure 9.7)

two-stage or two-spring injectors

This type of injector allows fuel to be gradually injected in two stages. This process assists in the control of com-bustion noise levels and to keep mechanical load low. Two springs with different ratings are used. The fuel is controlled and injected using the lighter or smaller spring to open the needle to a limited distance; this allows a small quantity of fuel to enter as a pre-injection amount, which is less than the standard injectors allow. The pressure and temperature in the combustion cham-ber begin to rise gently to start the ignition of the fuel. When the fuel pressure rises the tension of the larger or heavier spring is overcome, this allows the needle to be lifted further and the full amount of fuel is injected.

Hydraulic injector nozzles

The hydraulic injector nozzle and needle combination are used to inject a spray of fuel into the combustion chamber in a form to suit specific engine designs and to ensure the fuel will readily burn. To achieve this, various types of nozzles have been designed. They vary in length, the number of holes and the angle of the holes. The shape of the end of the needle can be flat, tapered or conical.

Hole angle

Hole angle

Angle of spray

Pintle DelayLong-stem

Single hole Conical-endsingle-hole

Multihole

Hole angle

FIgure 9.6 Types of injector nozzles


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injector servicing

Servicing the fuel system, particularly the injectors, ensures a finely atomised spray of fuel is injected into the combustion chamber. Incorrectly serviced or faulty injectors may cause misfiring, engine knock, engine overheating, loss of power, smoky black exhaust and increased fuel consumption. Check with the engine or system manufacturer for the correct service intervals. The following information is for minor servicing and injector checking in the workshop. For major injector overhaul, the manufacturer’s procedures and specifica-tions must be referred to. The overhaul of diesel pumps and injectors requires the utmost cleanliness and some specialised equipment. Therefore, major servicing and overhaul is best left to the specialised workshops that are equipped for diesel pump and injector overhaul.

locating a faulty injector

There are a number of ways to locate a faulty injector. Some can be performed on the engine but others require the injectors to be removed and tested.

isolating an injector

In some systems, faulty injectors can be isolated by loos-ening the injector pipe at each injector in turn, with the engine running at fast idle (see Figure 9.8).

Loosening each pipe cuts off the fuel supply to the particular injector and if the injector is faulty no change in engine speed will occur. If a noticeable drop in engine

speed is noted the injector is not faulty. This procedure is also used for checking and bleeding out any air in the fuel system that may be causing a problem.

On some engines it is not possible to gain access to the injector to crack open the line without extensive removal of other components; however, cracking the injector line at the pump produces the same result by removing the flow of fuel to the injector.

Isolating a faulty injector can also be achieved by using an infrared heat gauge or monitor to measure the tem-perature of the exhaust outlet or the injector for each cyl-inder. The temperature for each cylinder should be close to the same. If one cylinder is dramatically lower in tem-perature than the others, that cylinder could be the cause of the misfire.

checking injector spray

An injector can be checked for operation on the engine after it has been removed from the cylinder head. The injector is fitted to its pipe, but pointing away from the engine. The union nuts of the other injectors must be loosened, if they are still in place, to prevent fuel from being injected into the cylinders. The engine is cranked over with the starter so that the injector sprays into the air and the pattern of the spray can be observed. It should be a uniform fine spray, with no indications of wetness, streaks, side sprays or dribbles. When cranking is stopped, the nozzle should cut off and not dribble (see Figure 9.9). Ensure hands are clear of the injector while the engine is being cranked and wear safety goggles.

FIgure 9.7 Injector nozzles: (a) sac-hole nozzle, (b) seat-hole nozzle

(a)

(b)

Needle

Nozzle

Needle

Nozzle

Leak-offpipe

connection

Injectorpipe union

FIgure 9.8 Bleeding an injector pipe by loosening a union at the injector

Safety warning

The procedures described here for cracking injector lines and checking spray patterns must not be performed on a common rail diesel system due to the very high fuel pressure (see Chapter 8).


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testing injectors

A faulty or doubtful injector should be removed from the engine and pressure tested on an injector tester. As well as bench testing, test equipment is available for pressure testing the injection system in the engine while it is run-ning. This consists of a pressure gauge, valves and fittings connecting the injection pump and the injector. This will check the operating pressure, which can be used to assess the injector and the pump.

removing injectors

Before proceeding with any injector removal, ensure there is no dust, dirt or oil that can enter the cylinder and cause damage when the injector is removed.

When removing an injector, to ensure the injector pipe is not bent or distorted they should be disconnected at both the injector and the pump. The leak-off pipe should also be disconnected. This will ensure a correct reconnection, with no damage to the sealing surfaces and correct sealing with no leaks.

Injectors that are screwed into the cylinder head are removed with a special spanner that fits on to the body of the injector (see Figure 9.10).

Remove the bolts securing flanged injectors to the cylinder head. The injector can then be loosened with a special tool or lever, if necessary, and then removed (see Figure 9.11).

installing injectors

Before installing an injector, the recess in the cylinder head and the end of the injector must be clean. The wash-ers and heat shield for the particular injector should be new and must be in place.

threaded injectorCheck that it screws easily into the cylinder head. After seating in the sealing washers and heat shield, the injec-tor must be tightened to a specified torque. Always check

the manufacturer’s specifications. Over-tightening could cause the nozzle to deform and the needle could stick (see Figure 9.12).

Flanged injectorCheck that it is a free fit in the recess of the cylinder head. Use a new copper sealing washer. Tighten the bolts or nuts evenly so that the injector is not tilted. Tighten to the specified torque. Always check the manufacturer’s

FIgure 9.9 Injector operation: (a) spray pattern when pressurised, (b) condition when cranking stopped

Faulty

(a)

(b)

Good

Injector pipes

Leak-off pipe

Injectors

(b) Remove nuts holding leak-off pipe

(c) Remove injectors

(a) Disconnect injector pipes

Tool

FIgure 9.10 Removing threaded injectors from the cylinder head


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technical terms

• atomised spray

• combustion chamber

• common rail diesel (crd)

• conical

• dribble

• electrical discharge machining

• flanged injector

• fuel leak off

• hydraulic

• injector

• leak-off pipe

• misfiring

• multi hole

• needle

• nozzle

• pintle nozzle

• sac-hole

• seat-hole

• spark plug

• spindle

• spring

• tapered

specifications. Over-tightening could cause damage to the injector housing, seal and the nozzle.

Injector pipesAlways check the nuts for cleanliness and condition of threads and sealing flange. When being installed, the injector pipes should be checked at both ends to see that they fit squarely before the union nuts are connected.

union nutsTighten the union nuts at both ends of the injector pipes by hand. Then tighten with a spanner until the pipe is firmly in position. Over-tightening could cause damage to the sealing surfaces and threads. Always check for any tightening specifications.

FIgure 9.11 Flanged injectors are held in the cylinder head by bolts

Sealing washer

FIgure 9.12 Installing injectors: they should be tightened to a specified torque—the sealing washer is used at the base of the injector

Questions

1. What is a hydraulic injector?2. list the main components of a hydraulic

injector.3. using Figure 9.5, explain the basic

operation of a hydraulic injector.4. name at least two types of hydraulic injectors.5. name the different types of nozzles.6. explain the functions of:

a. the nozzleb. the needlec. the leak-off hose.

7. explain the purpose of:a. the sac-hole nozzleb. the seat-hole nozzle.

8. explain the term ‘dribble’ with regards to an injector.

9. describe the procedure for removing a hydraulic injector.


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10. describe the procedure for refitting a hydraulic injector.

11. the correct torque for tightening an injector after refitting is:a. 60 nmb. 35 nmc. as per manufacturer’s specifications.

12. Why is it considered dangerous to loosen an injector pipe on a common rail diesel?

13. before installing an injector, the recess in the cylinder head and the end of the injector must be clean. explain why.

14. Why is it important not to over-tighten an injector when refitting?

15. in addition to safety, correct components, specialised equipment, specifications and procedures, what is of utmost importance when servicing or overhauling a diesel fuel system?


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