volume 2 part 17 marine low speed diesel engines1

MEP Series, Volume 2, Part 17 Marine Low Speed Diesel Engines by Dr Denis Griffiths BEng (Hons), MSc, PhD, CEng, FIMarE Published by The Institute of Marine Engineers Published by the Institute of Marine Engineers 80 Coleman Street London Contents EC2R 5BJ Acknowledgement Copyright © 2000 The Institute of Marine Engineers A charity registered in England and Wales Reg No 212992 All rights reserved No part of this publication may be reproduced or stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright holders A CIP catalogue record for this book is available from the British Library ISBN 1-902536-33-9 paperback Typeset in Palatino with Helvetica Publishing Manager: Technical Graphics: Cover Design: J R Harris Barbara Carew Tma Mammoser Printed by Hobbs The Printers Ltd i I The Low Speed Diesel Engine 1.1 1.2 1.3 1.4 1.5 1.6 Engine Construction 2.1 Engine Structure 2.2 Bedplate 2.3 Frames 2.4 Cylinder Block 2.5 Tie Rods 2.6 Cylinder Liner 2.7 Cylinder Cover 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 2.25 3.1 3.2 3.3 Definition of a Low Speed Diesel Engine The Crosshead Engine The Crosshead Two-Stroke Operating Cycle Turbocharging and Supercharging Engine Parameters Piston Piston Rod Gland Crosshead Connecting Rod Bearings Crankshaft Camshaft Fuel Injection System Reversing Systems High Pressure (HP) Fuel Oil Pipes Fuel leakage Alarm Fuel Injectors Governors Lubrication Systems Engine Cooling Systems Combustion Air Supply Engine Chocking Vibration Safety, Additional Engine Systems, Monitoring and Control Crankcase Explosion Scavenge Fire Two-Stage Turbochargers 1 10 10 11 13 15 15 16 21 32 38 40 42 42 46 50 52 58 59 59 61 65 70 75 78 82 91 99 99 102 103 Power Take-In (PTI) Systems Electrical Generation Engine Monitoring Systems Unmanned Machinery Space (UMS) Engine Management Systems Noise 3.4 3.5 3.6 3.7 3.8 3.9 Engine Selection and Installation 116 Engine Selection Engine Air Supply Exhaust Gas System Turbocharger Choice Engine Services Engine Space Requirement Holding Down System Shaft Earthing Device 116 122 123 124 124 125 126 126 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 103 105 107 112 112 115 Engine Operation 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 Engine Starting Running Procedure Speed Adjustment Stopping Emergency Stopping Continuous Slow Running Cylinder Cut-Out System Emergency Running Turbocharger Failure Record Keeping Exhaust Emissions Engine Maintenance 128 128 131 140 140 140 141 141 143 144 145 146 148 Maintenance Maintenance Records Crankshaft and Main Bearings Connecting Rod Bearings Cylinder Inspection Cylinder Cover and Valves Chain Drive and Camshaft Turbocharger Cleaning Jacket Cooling Water System Oil Testing 148 151 152 154 155 159 160 160 163 163 Index 165 For Victoria Elizabeth Ryan my grand-daughter with love Acknowledgement No book is ever the sole work of an author, many people assist in various ways, and the author would like to express his thanks to all the individuals and companies who have assisted MAN B&W and Wiirtsilii-NSD have provided information to enable the author to complete the text and illustrations, without whose help this book could not have been produced Tony Woods at MAN B&W and David Brown at Wiirtsilii-NSD,in particular, were most helpful in locating information and answering particular queries Over the years the Institute of Marine Engineers has published many useful books that have assisted marine engineers throughout the world, and the author hopes this volume can be equally useful The Book Advisory Committee has been responsible for selecting suitable books and authors, the work of that committee going unnoticed by most people, and these efforts are available for all to see in the high quality of books for which the Institute is well known The author would like to express his thanks to all members of the Book Advisory Committee for the help they have given him and for the sterling work they have done on behalf of the Institute Finally the author would like to express his thanks to Joli Harris, formerly the Book Publications Manager, for her editorial help with this and other books, and for the valuable service she has performed in maintaining the high standard of the book publishing activities at the Institute The Low Speed Diesel Engine The Low Speed Diesel Engine 1.1 Definition of a Low Speed Diesel Engine The term 'low speed' is not exact but in marine terms it is generally accepted as an engine operating at a speed below about 200 revolutions per minute In addition to this, low speed engines are invariably of the crosshead type and operate on the two-stroke cycle This has not always been the case, however, since its introduction the century of marine diesel engine evolution has produced an almost standard arrangement, something designers were looking towards during the 1920s.At the beginning of the 21st century there are still a number of different designs of low speed crosshead engines powering merchant ships but many of these designs have not been built for almost twenty years and can now be considered obsolete In order to ensure this title meets the needs of current and future seagoing engineers only those designs in production during the final decade of the 20th century will be considered in detail within this MEP 1.2 The Crosshead Engine There are essentially two separate sections to any marine diesel engine, the cylinder in which power is developed and the crankcase where reciprocating power developed by the piston is translated into rotary power at the crankshaft (Figure 1) This arrangement follows from the reciprocating steam engine developed in the latter part of the 19th century, where the cylinders are mounted above the crankcase A diaphragm separates the power cylinders from the crankcase preventing combustion products from the cylinders from contaminating the crankcase lubricating oil The diaphragm also acts as the bottom of the scavenge air trunking which surrounds the lower part of the cylinder liner A gland allows the piston rod to pass through the diaphragm while preserving the seal between scavenge trunking and crankcase Current engines are of the single-acting type which means that combustion only takes place in the portion of the cylinder above the piston, unlike the double-acting engine in which combustion would also take place below the piston requiring a lower cylinder cover through which the piston rod had to pass The Low Speed Diesel Engine 1.3 The Crosshead Translation from the reciprocating motion of the piston to the swinging action of the connecting rod requires a bearing and this is provided by the crosshead, the upper end of the connecting rod is attached to the crosshead pin, by means of bearings, which is firmly bolted to the piston rod The lower end of the connecting rod is attached to the crank pin and as the engine operates the forces in the piston rod and connecting rod vary with time and the angular position of the connecting rod, which changes as the crankshaft rotates The angularity of the connecting rod causes a side thrust to be exerted at the crankshaft and the crosshead Both of these side thrusts have to be resisted and while the crankshaft side thrust is dealt with readily by the crankshaft bearings, the crosshead side thrust has to be countered by the use of guides Guide shoes, fitted to the crosshead, run in sets of guide bars which act to resist the side thrust due to the angularity of the connecting rod which prevents the piston from rubbing against the cylinder liner wall The guide arrangement also accommodates the side thrust which occurs when the ship rolls, and keeps the piston aligned with the axis of the cylinder liner Fore and aft rubbing faces on guide shoes and guide bars accommodate thrust due to pitching of the ship (Figure 2) The Low Speed Diesel Engine The Low Speed Diesel Engine 1.3.1 Astern Guides As shown in Figure the connecting rod side thrust acts in opposite directions during the power and compression stroke of the piston so it is necessary to provide guides to accommodate both directional forces The force produced during the downwards power stroke of the piston is greater than that produced during the upwards compression stroke because the maximum pressure during combustion is higher than that due to compression of the air during the compression stroke (see Section 1.4, on the two-stroke cycle) Under such circumstances it might be presumed that a smaller guide area could be used for the guide acting during the compression stroke, however, apart from the idea of using the same sized components there is a very good reason for having identical guide shoes and guide bars The majority of low speed engines are directly connected to the propeller shaft and are of the reversible type, hence the engine rotational direction is changed so that the ship's direction may be reversed When the engine operates in the reverse (astern) direction the angle of the connecting rod during the power stroke of the piston is opposite to that when turning in the normal (ahead) direction and, hence, so is the direction of the force acting on the guide This means that a large astern guide face is needed; even if the engine was not reversible standard terminology refers to the two guide faces as ahead and astern 1.4 above that of the exhaust gas, is directed into the cylinder it will remove the remaining exhaust gas and at the same time provide the new air charge for compression This process is known as scavenging Over the years a number of different scavenging systems have been adopted but there are currently only two in common use, 'Uniflow' employed by most engines of current design, and 'Loop Scavenging' used by the Sulzer RND, RND-M and RL engines Two-Stroke Operating Cycle (Figure 3.) Power is produced in the cylinder of an engine by the combustion of fuel oil, producing a high gas pressure which forces the piston downwards In order to bum the oil sufficient air (oxygen) must be available in the cylinder and that air must be at a very high temperature in order to ignite the fuel oil when it is injected into the cylinder The diesel engine is a compression ignition engine which means that compression of the air charge produces the high temperature for ignition Following expansion of the hot combustion gases during the power stroke of the piston the waste, or exhaust, gases must be removed from the cylinder in order to allow the fresh air charge to enter With a single-acting engine the two-stroke operating cycle allows for one power stroke for every revolution of the crankshaft or two strokes of the piston As the downward piston stroke produces the power and the upward stroke achieves compression of the air charge it follows that removal of the exhaust gas from the cylinder and its replacement by a fresh air charge must take place while the piston is near the bottom of its stroke When the exhaust passage from the cylinder is opened the waste exhaust gas will flow out but there will still be exhaust gas in the cylinder If a fresh air supply, at a pressure 1.4.1 Uniflow Scavenging (Figure 4a.) Exhaust gas leaves the cylinder via a large exhaust valve located in the cylinder cover and scavenge air enters through a number of ports cast in the lower portion of the cylinder liner The valve is opened slightly before the scavenge ports are uncovered, this is known as the blowdown period, and the cylinder pressure falls below the scavenge air pressure by time the scavenge ports are uncovered Exhaust valve opening and closing can be adjusted as the valve is actuated through a camshaft (see Chapter 2) but the scavenge ports are uncovered and covered by the piston so the scavenge timing is set and cannot be adjusted When the downwards moving piston uncovers these ports air enters the cylinder and moves towards the lower pressure region of the exhaust trunking, which effectively removes the remaining exhaust gas from the cylinder (this is the scavenging part of the gas exchange process) As the piston moves upwards during the compression stroke the scavenge ports are covered thereby cutting off further air supply to the cylinder, however, the exhaust valve is still in the process of closing and so some of the air is lost from the cylinder (this is the post-scavenge period) This The LowSpeed Diesel Engine The LowSpeed Diesel Engine loss of air has to be accepted as part of the engine design as it is not possible to close the exhaust valve instantaneously when the scavenge ports are covered, nor is it advisable to begin closing the valve before the scavenge ports are covered as that could reduce the effectiveness of the exhaust gas removal process The amount of air loss during post-scavenging can be calculated and an allowance made when determining the quantity of fuel to be injected of the air charge could be lost In order to overcome this problem Sulzer fitted a rotary exhaust valve in the cylinder exhaust passage which would rotate and effectively close the exhaust passage even though the ports were still uncovered The RD engine had a relatively short piston skirt which meant that exhaust ports were uncovered during the compression stroke, and the rotary exhaust valve effectively closed the exhaust passageway during the compression stroke 1.5 Figures4a.and 4b UniflowScavengingand LoopholeScavenging 1.4.2 Loop Scavenging (Figure 4b.) Sulzer engines constructed up until the 1980s employed Loop Scavenging for the gas exchange process The RND, RND-M and RL engines did not have exhaust valves The exhaust gas left the cylinder via ports cast in the cylinder liner above and to one side of the scavenge air ports, and both sets of ports were controlled by the piston As the piston moved downwards it first uncovered the exhaust ports and cylinder pressure fell as exhaust gas escaped By the time the scavenge ports were uncovered the cylinder pressure was below the scavenge air pressure and incoming scavenge air forced out the remaining exhaust gas Scavenge ports were angled and the upper sides of the piston chamfered in order to direct the incoming scavenge air towards the top of the cylinder so that the exhaust gas would be effectively removed The piston controlled the opening and closing of the exhaust and scavenge ports so that timing was symmetrical, giving identical blowdown and postscavenge periods For an earlier Sulzer engine, the RD type which employed a pulse system of turbocharging, there was a large blowdown period and consequently an equally large post-scavenge period during which a great deal Turbocharging and Supercharging As mentioned, a two-stroke cycle engine requires scavenge air to be supplied at a pressure above that of the atmosphere in order to ensure that the exhaust gas is removed from the cylinder and a fresh air charge is available for the next cycle This air can be supplied by a number of systems including engine driven rotary blowers, engine driven reciprocating pumps or electrically driven rotary blowers However, since the 1950s it has been the practice to employ rotary compressors driven by single stage gas turbines which derive their energy from the engine exhaust gas Use of such gas has many advantages including an improvement in operating efficiency and an increase in power available at the crankshaft as no power is removed to drive the scavenge pumps or blowers Supercharging is a means of increasing engine power output by increasing the air supply which enables more fuel to be burned A supercharger can be any device which increases the pressure of the combustion air supply above that which is normally required A supercharger can be a turbocharger but it can also be any of the other devices which increase air pressure A turbocharger can be a supercharger, but only if it supplies air to the engine at a pressure just above that which is needed for effective scavenging The effect of supercharging can be seen from the following equations: pv=mRT whichgivesm = pv/RT where: p = Cylinder pressure (N/m ) v = Cylinder volume (m3) R = Gas constant Ikg K) T = Air temperature (K) (Celsius Temperature + 273) a The cylinder volume when the scavenge ports are covered is constant, and if the air temperature is kept constant then the mass of air varies directly with the pressure Doubling the pressure will double the mass of air in the cylinder and, theoretically the fuel mass burnt may be doubled to allow for an increase in power developed A critical factor in this is the air temperature which is dealt with in more detail in Section 2.23.3 on Air Coolers The Low Speed Diesel Engine 1.6 The Low Speed Diesel Engine Engine Parameters The size of an engine depends upon a number of factors and an important feature is the power to be developed Naturally the number of cylinders will govern the power of the engine but the bore of the cylinder and the length of the stroke will determine the power developed in the cylinder The standard equation governing a two-stroke cycle engine cylinder power is as follows: Power (Watts) = Pm X A X L X n (N/m2) Where: Pm = Mean cylinder pressure A = Piston area (m2) L = Length of piston stroke (m) n = Revolutions per second (lis) Note: Sometimes the acronym PLAN is used in order to aid recollection of the cylinder power calculation The cylinder bore governs the value of 'A' and this can vary from 980mm for large engines down to 260mm for the smallest engines During the final decade of the 20th century brake mean effective pressures have increased from about 18.0bar to 19.0bar and at the same time maximum cylinder pressures have risen from about 135bar to 150bar 1.6.1 Stroke to Bore Ratio Engines today have a stroke to bore ratio of between 2.5:1 and 4:1 depending upon the application The piston speed for normal running is governed by the rate at which combustion takes place and the expansion of the gas produced by combustion of the fuel Maximum piston speed occurs during the middle of the piston stroke and the effect of the expanding gas acting upon the piston should be such to exert an even rotation of the crankshaft During the 1990scrosshead engine designers adopted mean piston speeds of 8.0ml s or slightly above 1.6.2 1.6.3 Specific Fuel Oil Consumption (SFOC) The emphasis on engine design has been to improve reliability, ease of maintenance and fuel efficiency A Specific Fuel Oil Consumption (SFOC) of 170g/kWh (125g/bhph), based upon full load brake power, is expected from engines designed during the late 1990s 1.6.4 Engine Dimensions The crank throw of a long stroke engine is longer than that of the normal or short stroke counterpart (crank throw is half the piston stroke) and so a long stroke engine would require a wider and deeper bed plate in order to accommodate the crankshaft To keep the angularity effects of the connecting rod within reasonable limits the length of the connecting rod is generally increased and these factors, together with the increased length of the cylinder liner, mean that a long stroke engine would tend to be much taller than a normal or short stroke engine of the same bore In practice the availability of improved bearing materials means that the loading on bearings can be increased without adverse effect and so the connecting rod length of a long stroke engine can be reduced, which has the effect of reducing engine height and width Engine length depends upon the bore and number of cylinders but engine designers try to get the centres of the cylinders as close as possible in order to keep engine length to a minimum Cylinder liners are located in cast cylinder blocks which provide the cooling water jacket and space has to be provided to accommodate these, but it is not just the cylinders which dictate engine length, particularly for the smaller bore engines Bottom end and main bearings must be of a defined length in order to provide for a large enough bearing area to resist the load Crank webs must also be of sufficient width to provide crankshaft rigidity The influence of these is significant with small bore engines and can result in a longer engine than the bore alone might indicate Size also influences weight and a large engine is also a heavy engine Long Stroke Engines By allowing the gas to expand further greater fuel efficiency is obtained because more energy is obtained from the expanding gas, however, this requires a longer piston stroke and that in turn results in a lower rotational speed Slower rotation of the propeller generally increases propulsive efficiency and long stroke versions of a particular engine will often be selected for the propulsion of large bulk carriers due to the higher overall efficiency Such an engine is, however, taller and wider than the short stroke version and would require more engine room space, although the space available for the main engine in a bulk carrier is generally not restrictive Engine Construction Engine Construction 2.1 Engine Structure The engine structure must be sufficiently rigid to ensure the crankshaft does not bend excessively when it is subject to cylinder peak pressures during ignition In addition the guide's forces must be accommodated without distortion and the frames must adequately support the cylinder block (called a cylinder beam by Sulzer), air box and turbochargers The frames are mounted on the upper face of the bedplate using small diameter frame feet bolts and the cylinder block attaches to the upper face of the frames using similar fitted bolts Pairs of tie rods, located at the main bearings, hold the entire structure in compression but the small fitted bolts are still needed, particularly at the frame feet, in order to accommodate the side thrust due to the reaction at the guides Mating faces between the bedplate, frames and cylinder block are machined While the structure must be strong enough and rigid enough to take the loading it should also be as light as possible and careful design is needed to ensure stresses remain within acceptable limits High varying stress can result in fatigue failure of components Modem design achieves strength and lightness by treating the structure as a composite and not as separate parts and in that way each part not only serves its particular purpose but it also provides strength and support to other parts of the structure 2.1.1 Fatigue Cracking Fatigue may be defined as the formation and propagation of a crack under the action of a varying tensile stress The stress must vary with time and it must be tensile A compressive stress causes crack faces to be forced together and so the crack cannot propagate, while a static stress does not produce the change in the grain structure of the material which is essential for fatigue crack propagation Fatigue cracks form and propagate at stresses way below that which would produce tensile failure in the material but a common factor in fatigue cracking is the presence of stress raisers These may be existing small cracks, gas inclusions, slag inclusions, or sharp changes in section due to poor design and damage The stress applied to a component may be well below that which would cause a fatigue crack to develop or grow but around the stress raiser the stress level rises considerably and it is at these locations that fatigue cracks form As the crack develops the area resisting the stress is gradually reduced and so the actual stress rises, resulting in an increased rate of crack growth Eventually the remaining cross-sectional area of the material is unable to resist the applied load and sudden failure occurs The fracture 10 Engine Construction surface of a component which has failed in fatigue exhibits two distinct surfaces, the shell-like or polished surface of the fatigue crack as it propagates through the grains of the material and the brittle surface of final failure In order to reduce the risk of fatigue failure the loading on a component must be kept within defined limits, but care must also be exercised in order to restrict the presence of stress raisers While it is difficult to know about the presence of gas or slag inclusions unless X-ray or a similar technique is applied, and these are prohibitively expensive, good design will avoid sharp changes in section and care during maintenance will prevent mechanical damage which results in stress raisers 2.2 Bedplate (Figure 5.) The bedplate supports the crankshaft and provides the foundation for the remainder of the engine structure, consisting of longitudinal steel girders joined by cast steel cross or transverse girders which support the main bearings Fabrication is employed for bedplate construction and only the transverse girders are cast The use of casting eliminates residual stresses which might be present if the girders were fabricated as residual stresses are always present in welds (see below) EngineOperation EngineOperation 5.3 Speed Adjustment While the engine is operating via remote control speed is adjusted by the control system which changes the speed setting of the governor The governor then adjusts the fuel pumps Even if the engine is operating via local control fuel pumps are adjusted via the governor However, speed changes must always be undertaken gradually to avoid rapid cylinder load fluctuations which could have an adverse effect on the cylinder oil film and piston rings As previously stated, rapid load changes can cause temporary surging When manoeuvring sometimes the auxiliary blowers need to be started so that sufficient scavenge air is supplied during low speed operations The engineer must be aware of this requirement and ensure the blowers are started at the appropriate time 5.4 Stopping Removing the fuel supply from the fuel injectors will cause the engine to stop There are no particular problems associated with this apart from the fact that there is no cooling requirement when the engine is stopped and heating will be required in order to maintain cylinder and piston temperatures Although the control system should perform all necessary adjustments the engineer should double check to ensure all the necessary adjustments have actually been made and that cylinder temperatures are held within narrow limits 5.5 Emergency Stopping It may be necessary for the ship's speed to be reduced rapidly and the engine can be run in the reverse direction to help achieve this It should be realised, however, that when rotating in the reverse direction the propeller will only thrash water if the ship's speed is still high If fuel is simply removed from the engine the propeller, and hence the crankshaft, will still rotate due to the effect of the water on the propeller which will have little or no effect on the ship's speed A better arrangement is to gradually reduce engine speed until the engine is running at its lowest speed as this allows the propeller to exert a drag effect on the ship's motion When the ship's speed has reduced to a reasonable level the engine may be stopped and started in the reverse direction If there is a requirement for a crash stop in which the Bridge takes responsibility for possible engine damage it should be understood by all of the engineering staff that the Bridge requires the engine to be operating at maximum speed in the reverse direction as soon as possible Different engine builders have different instructions relating to manual crash stops but the general requirements are as follows: 140 Acknowledge the instruction by answering the telegraphs Move the control lever to the stop position While the engine speed is reducing ensure that starting air is available at the engine and that coolers and other engine support systems receive the necessary attention When engine speed has fallen to the reversing value (15 per cent to 30 per cent of MCR speed) operate the control to engage the reversing system and apply starting air When the engine has reached the required speed of rotation in the reverse direction, apply fuel With some engines it is possible to brake the engine speed in the ahead direction by applying starting air in the reverse direction before the reversing value has been reached This should only be done with care and after the crash stop has been signalled All engineers should make themselves fully aware of the instructions for emergency reversal and crash stops as soon as they join a particular ship; it is too late to find out what they are when faced with an emergency situation 5.6 Continuous Slow Running If the engine is to be run continuously for prolonged periods at reduced speed there is a risk of deposit build-up in the cylinders, on the exhaust valves, the turbine blades and in the uptakes This is a result of poor combustion due to the fact that slow running produces imperfect atomisation When manoeuvring the carbon deposits are light and burn away quickly when the engine resumes full speed, however, if the engine will need to run for a prolonged period at low speed some rectifying action is required The fitting of 'slow steaming' nozzles to the injectors will improve atomisation as the smaller area of the nozzles compensate for the reduction in fuel pressure due to slow running so the correct fuel droplet size is produced Prior to resuming normal speed the 'slow steaming' nozzles must be replaced by normal nozzles otherwise very fine fuel droplets will be produced which will have a detrimental effect on fuel combustion The return to full sea speed should be undertaken gradually in order to avoid the possibility of scavenge fires 5.7 Cylinder Cut-Out System (Figure 78.) As with continuous slow running, at very low engine loads defective atomisation occurs There is also the problem of irregular fuel injection due to jiggling of the governor and/ or play in the connections of the fuel pump rack system The effect when operating close to the minimum fuel injection amount is that sometimes there may be just enough index on a fuel pump to inject fuel while at other times there may be insufficient index to so This results in erratic operation with cylinders failing to fire at times 141 EngineOperation EngineOperation In order to overcome this problem one engine builder has introduced a cylinder cut-out system which cuts off fuel to about half of the cylinders when operating at very low speeds Those cylinders receiving fuel operate normally with adequate fuel pump index to prevent problems In order to avoid the build-up of cylinder lubricating oil in those cylinders which are temporarily cut-out, the shutting off of fuel is made in turns between groups of cylinders so that each group is operated under load for a period of time thereby burning off surplus cylinder oil and maintaining the same thermal load on all cylinders Cylinder groupings are chosen to ensure the firing order is as smooth as possible to minimise vibration In order to obtain effective starting the cut-out system is disabled during manoeuvring and until the engine has stabilised Fuel pumps are deactivated by sending pressure air to the puncture valve at the top of the fuel pump which prevents pressure oil from passing to the fuel injectors of that cylinder 5.8 Emergency Running There are times when engine defects cannot be rectified immediately yet the engine must be operated in order to make the next port The engineer must be aware of how the engine can be run safely under such circumstances At all times safe conditions in the engine room must exist and there must be the minimum of subsequent damage to the engine 5.8.1 Cylinder Cut-out An engine is designed to run in balanced condition with all cylinders functioning and developing approximately the same power If for some reason a cylinder has to be cut-out the engine will no longer be in mechanical or thermal balance and it must be operated at reduced loading Defects such as a wiped crosshead bearing, cracked cylinder liner, cracked piston, or defective cylinder cover which cannot immediately be replaced, mean the engine must run with the affected cylinder cut-out It is not simply a case of shutting off fuel to the cylinder concerned as each cylinder has an influence on other cylinders and other parts of the engine Torsional vibration may be a problem at certain speed and the engine builder must be consulted for advice as to the speed ranges which must be avoided with a particular cylinder cutout Turbocharger surging may occur making it necessary to reduce the operating speed below that which the remaining cylinders could maintain Hunting of the governor may take place and if this happens the governor must be adjusted until the hunting ceases With electro-hydraulic governors the stop screw on the changeover mechanism must be screwed down until the hunting ceases while electronic governors must be operated on 'index 143 Engine Operation Engine Operation control' Depending on the reason for cutting out a cylinder unit the starting air system on that unit mayor may not remain operable If it does the engine is fully manoeuvrable but if starting air is shut off to the cylinder there may be a dead spot where the engine may not start Giving the engine a short burst of starting air in the opposite direction may move the engine from the dead spot but if this does not work the turning gear must be employed If the piston has to be removed from the cylinder it is necessary to disable the air start system, exhaust valve operating mechanism, cylinder lubrication and piston cooling and also to blank off the hole in the diaphragm gland If the engine has a cracked liner or cylinder cover the jacket cooling water must also be isolated Failure of a crosshead or bottom end bearing requires the crosshead assembly, including the connecting rod, to be disconnected from the crankshaft and secured in a safe position within the crankcase or, preferably, removed from the crankcase completely All lubrication supply paths to that unit's bearings must be isolated to prevent loss of lubrication pressure Because an engine's response to the removal of power from a cylinder differs with engine size and the number of cylinders, the opinion of engine builder should always be sought before operating the engine 5.9 Turbocharger Failure A two-stroke cycle engine requires an air supply under pressure for scavenging, therefore, failure of a turbocharger has serious implications, particularly if the engine only has one turbocharger Severe vibrations due to impeller or turbine blade damage, bearing failure or fracture of the water cooled casing all require the turbocharger to be put out of operation There are many other reasons why it might be considered advisable to reduce turbocharger speed or disable the turbocharger completely and the engineer must always be mindful of the possible consequences of allowing a defective unit to continue in operation The immediate action taken in the event of discovering a damaged turbocharger depends on the nature of the damage and the current situation of the ship If the ship is manoeuvring when the damage occurs the load should be reduced until vibrations cease 5.9.1 Disabling a Turbocharger The action taken to disable a turbocharger depends upon the facilities available and the design of the installation If there is only one turbocharger it is important to ensure sufficient air reaches the auxiliary blower If the auxiliary blower takes its suction from the engine room no action need be taken, however, if suction is taken from the turbocharger compressor outlet the compensator located between the compressor outlet and the scavenge air 144 suction must be removed to reduce auxiliary blower suction resistance Because of the lower air supply which is available from the auxiliary blower the engine must be run at reduced load The turbocharger must be isolated and there are two arrangements in general use, both of which assume the turbocharger operates on the constant pressure system L Engines with Exhaust By-pass Lock the turbocharger rotor and remove the blanking plate from the exhaust by-pass pipe In some cases the by-pass pipe is not a permanent fixture and must be fitted Insert blanking plates to turbine inlet and outlet to prevent flow of exhaust gas through the turbocharger L Engines without Exhaust By-pass Remove the rotor and nozzle ring from the turbocharger and insert blanking plates to isolate the air side and bearings from the gas side of the turbocharger There will be a flow passageway for the exhaust gas to go directly from the turbine inlet to the turbine outlet For engines with two or more turbochargers (again assuming operation on the constant pressure system) the rotor of the defective turbocharger may be locked and orifice plates inserted in the compressor outlets and turbine inlets The small air flow that this allows provides for compressor cooling while the small gas flow through the turbine prevents corrosion Engine load restrictions will apply and the auxiliary blower may be operated as required depending on scavenge air demand 5.10 Record Keeping An assessment of engine performance can only be made if the relevant engine parameters are monitored and recorded Trend analysis requires data to be recorded over a period of time It is also important to record operating hours for various engine components because certain items, particularly ball or roller bearings, must be replaced on an operating time basis to minimise the risk of failure due to fatigue The use of computer monitoring systems greatly assists the engineer in monitoring, record keeping and analysis because, in most instances, the process is automatic and requires no manual intervention apart from retrieval of information In some cases the engineer does have to manually record data and it is essential that the correct information is recorded at all times During maintenance readings of dimensions might be required together with information on the condition of a component The operating hours since the previous overhaul and the spare parts used during the repair or overhaul must also be manually recorded Any computer system 145 EngineOperation EngineOperation is only as good as the information stored and it is the responsibility of the engineer to ensure accuracy is maintained 5.11 Exhaust Emissions The burning of any fuel creates exhaust gases or emissions and most of these have an effect on the environment The quality of the fuel oil being burnt influences the level and type of emission, however, cylinder lubricating oil also produces emissions as it is a hydrocarbon and contains chemical additives The International Maritime Organisation (IMO) is proposing to limit engine emission levels at sea but other bodies, particularly the American Environmental Protection Agency, are also formulating rules governing emission levels Exhaust gas components following combustion are; Oxygen: Present due to the excess air supplied to the engine It is not harmful but reduces the concentration of the other gases in percentage terms Nitrogen: Comprises over 70 per cent of the atmosphere It is not harmful but also reduces the concentration of the other gases in percentage terms, and can react with oxygen at high temperature to produce harmful Oxides of Nitrogen (NOx)· Water Vapour: Product of the combustion of hydrogen with no harmful effects Carbon Dioxide: Produced due to the complete combustion of carbon Although non toxic carbon dioxide does not support life and it is also a 'greenhouse gas' which is undesirable Carbon Dioxide is produced whenever a hydrocarbon fuel is burned and the only way of limiting its production is to burn a low or zero carbon fuel This is not possible with hydrocarbon fuels and it has to be accepted that the production of carbon monoxide is a part of diesel engine operation Oxides of sulphur cause corrosion in the engine and in the atmosphere this produces acid rain and can lead to breathing difficulties The only way of reducing emissions of SOx is to burn a low or zero sulphur fuel or by washing the exhaust gas in a scrubber Oxides of Nitrogen:These are formed during combustion and result from the chemical combination of oxygen and nitrogen at high (NOx) temperature As both of these gases are m the atmosphere their formation is unavoidable Two-stroke cycle engines are optimised for high efficiency and this means high maximum cylinder temperatures which in turn result in high levels of NOx formation NOx contributes to the formation of 'Smog' and acid rain and they also cause damage to lung and other delicate tissue Reduction may be by engine based or primary methods, or by secondary methods, effectively the fitting of a Selective Catalytic Reduction (SCR) unit Primary cylinder maximum reducing involve methods temperature by delaying fuel injection or through the use of emulsified fuels or water injection These systems tend to increase fuel consumption and CO2 emissions SCR requires the fitting of a catalytic unit in which the NOx is reduced to harmless components through reaction with a chemical injected into the exhaust gas flow Other emissions include smoke and particulates which result from poor combustion, ash in the fuel, cylinder oil and deposits coming loose from the combustion chamber or exhaust gas system The topic of diesel engine exhaust emissions is covered in greater detail in MEP Series, Volume 3, Part 20: Exhaust Emissions from Combustion Machinery by A.A Wright, ISBN 1-902536-17-7 Carbon Monoxide: It is formed due to the incomplete combustion of carbon and represents a waste of energy It is a toxic gas and is to be avoided Oxides of Sulphur: Produced by the burning of sulphur which is present in (SOx) the fuel oil During combustion different oxides of sulphur are produced, mainly S02 and S03, the levels of which are a function of the amount of sulphur in the fuel 146 147 EngineMaintenance EngineMaintenance Engine Maintenance 6.1 Maintenance Table Typicalintervals for maintenanceof EngineParts Item Engine components wear at different rates and replacement parts should be replaced before wear results in failure which could cause serious damage to other engine parts The extent of any wear must be established by taking measurements after dismantling a particular section of the engine, or by using probes located in components such as cylinder liner walls or bearings Abnormal cylinder liner wear, like scuffing or piston burning, can be detected by visual inspection and a decision made to replace the part or investigate further Although wear is a major cause of parts having to be replaced it is not the only one As previously discussed, some components are subject to varying tensile stress which can lead to fatigue cracking which, in turn, can result in catastrophic failure should the crack become too large Ideally components subject to the risk of fatigue should be inspected and the extent of the cracking determined A decision can then be made whether or not to replace the component This is not practical, however, as it would require much of the engine to be dismantled and expensive methods to be employed to detect the crack The decision to replace parts is therefore made on the basis of operating hours, which indicates the number of stress reversals if the operating speed is known This means a component is taken out of service long before any cracking is significant The component often has a considerable period of useful service left, however, this method provides a safety buffer against failure During maintenance only the approved tools supplied by the engine builder should be employed and all lifting equipment should have been tested and have a current certificate Hydraulic jacking equipment for tightening nuts should be treated with great care as injury can be caused by high pressure oil leakage or from fragments of sealing ring blowing out During maintenance only the approved tools should be used as the use of unsanctioned methods and equipment, such as two pieces of rope or rag to open up the butts of piston rings when replacing rings, is not only likely to be dangerous but can impose additional stresses on the components resulting in early failure 6.1.1 Maintenance schedules (Table 2.) Maintenance schedules proposed by engine builders offer a guide to the recommended intervals between overhaul and replacement of parts and should be used initially, then amended in light of subsequent operating experience 148 Bedplate Main Bearing Interval Work Initial Subsequent Retighten holding down bolts - 8000 hours Every 15 - 20000 hours Measure clearance - 8000 hours Every - 8000 hours As required Dismantle and inspect Thrust Bearing Tie Bolts Diaphragm Gland Measure clearance 15 - 20000 hours Every 15 - 20000 hours Inspect thrust pads As required As required Retighten - 8000 hours Every 35 - 40000 hours Retighten vibration dampers 500 hours Every - 8000 hours At piston removal Clean and inspect Check ring clearance Every - 8000 hours - 8000 hours Replace rings As required Gauge bore At piston removal Re-shape lubricating grooves As required Cylinder Cover Inspection of combustion chamber At piston removal Exhaust Valve Clean and regrind (if needed) - 4000 hours Every - 4000 hours Detailed inspection and measure - 8000 hours Every - 8000 hours Removal inspection and check rings and grooves - 8000 hours Every - 8000 hours Cylinder Liner Piston Dismantling of piston As required Visual inspection of piston and rings Every 500 hours through scavenge ports Inspection of piston crown When removing piston & exhaust valve Piston Rings Check rings & clearances; replace if necessary When removing piston Cams Inspect running surfaces - 4000 hours Every - 4000 hours Camshaft Drive Inspect gears/ chains - 4000 hours Every - 4000 hours Governor (Hydraulic) Check oil level - 2000 hours Every - 2000 hours Change oil - 2000 hours Every - 8000 hours 149 Engine Maintenance Engine Maintenance Turbocharger Dismantleand cleancompressor Inservicecleaning ofturbine Dismantleandclean turbineside FuelInjector Injectoratomisation Cleanand overhaulnozzle StartingAirValve Inspect,clean andreface Crankshaft Takedeflections ConnectingRod Measureclearance Bearings Crosshead Measureguide clearance Inspectpinand bearingsurfaces ChargeAir Tubeclean(airside) Cooler Tubeclean(waterside) CylinderSafety Removeforinspection Valve Testliftingpressure Cylinder Cleaninletfilter Lubricator Inspectionof drivinggear FuelInjection Dismantle,inspect Pump andretime SystemLubeOil SpotTest Chemicalanalysis JacketWater Chemicalanalysis StartingAir Dismantleandinspect ControlValve - 4000 500 hours hours Every2 - 4000 hours Every500 hours - 8000 hours Every6 - 8000 hours - 4000 hours Every2 Asrequired 4000 hours - 8000 hours Every6 - 8000 hours - 4000 hours hours Every2 Every6 - 4000 - 8000 8000 hours hours - 8000 hours Every6 - 8000 hours Asrequired - 8000 hours Every6 - 8000 hours - 8000 hours hours Every6 Every6 - 8000 hours hours - 4000 hours hours Every6 Every2 - 4000 hours hours - 8000 hours Every6 - 8000 hours - 8000 - 8000 - 8000 hours Every6 - 8000 8000 8000 hours hours Every500 hours hours Every2 - 4000 hours Asrequiredto supplier'sinstructions 20000 hours Every15 - 20000 hours 500 - 4000 15 - Table Typical intervals for maintenance of Engine Parts Maintenance intervals are influenced by the likes of the quality of the fuel oil being burned, ahnospheric conditions (e.g a dusty environment) and prolonged slow running of the engine The quality of any spare parts used also has an influence on operating life and it is essential than any components fitted to the engine be made from materials which can withstand the loadings expected for the anticipated operating interval With respect to the intervals 150 between the overhaul of engine parts the figures quoted in Table are typical, although not the same for all engines The use of a particular component or material mostly depends on the experience of the engine builder Maintenance schedules are designed to ensure effective operation of the engine with the minimum risk of breakdown due to component failure or malfunction It is in the interest of the engine builder that the engine performs to expectation and has as long an interval between replacement of parts as possible Indeed repeat engine sales and reputation depend on such matters It is no accident that many different components in an engine have the same interval between routine maintenance If an engine has to be stopped to allow the inspection of one component it is reasonable to inspect others at the same time, particularly as the actual replacement of a part takes longer than inspection and costs more as spares have to be used Engine builders attempt to extend the life of components through design and use of higher quality materials, but the aim is always to replace the part before failure takes place Genuine spares should always be used as this is the only way to guarantee the quality of materials and manufacture The use of 'pirate' spares, with their lower initial cost, may appear to be advantageous but is almost always a false economy due to the risk of engine failure, subsequent increased maintenance and possible ship 'down-time' Operational matters are outside the engine builder's control and so maintenance intervals are only recommendations It is up to the engineer to decide whether to extend or reduce the interval between maintenance for particular components and that decision must be based upon observation and experience 6.2 Maintenance Records Records of clearances and component conditions obtained during previous overhauls allow the engineer to make decisions as to future maintenance intervals and complete records are essential to this analysis No engineer remains on the same ship indefinitely and it is important that all engineers maintain detailed records of all maintenance in a form which can be readily understood by engineers who later join the ship Computer systems for engine management often include record sheets for maintenance and these allow a complete picture of all events for a particular system to be developed Persistent engine defects or poor performance may be due to common factors such as fuel quality or imperfect spare parts but it can be difficult to isolate the cause to such a source unless all the relevant information has been recorded Frequent failure of, say, fuel injector nozzles may be due to many reasons including the quality of the fuel, cylinder combustion and the material used to manufacture the nozzles If nozzles begin to suffer damage after bunkering a particular fuel oil then the cause is likely to be the fuel, however, if only certain nozzles from a 151 Engine Maintenance particular batch supplied to the ship are becoming damaged then the source of the spares is the probable cause A proper analysis of the situation be only be made if all the relevant information has been accurately recorded 6.3 Crankshaft and Main Bearings The crankshaft sits in bearings which are located in the bedplate, distortion of the bedplate or uneven wear at the bearings will cause the crankshaft to bend when it comes under load, resulting in high local stresses and possible fatigue failure Bedplate distortion is due to worn chocks 5teel or cast iron chocks should be checked visually and by tapping with a hammer Holding down arrangements should be retightened at about 12 000 hour intervals, or more frequently if loose chocks are detected Resin chocks are not prone to fretting but the holding down arrangement should be retightened periodically to ensure the bedplate is correctly held in contact with the tanktop 6.3.1 Main Bearings (Figure 79.) Clearance at the main bearings can be assessed without dismantling the engine by using feeler gauges Care must be taken when inserting the feeler gauge so as not to bend the blades and damage the journal or bearing surface 6.3.2 Crankshaft Deflections Checking crankshaft deflections should be done with the ship afloat The load and trim of the ship will cause the hull to distort slightly which can have an influence on the bedplate, therefore, deflections should, ideally, be taken at the normal load and trim conditions for the ship Deflections are comparative and should be taken when the ship is at the same load and trim conditions as for previous readings Engine temperature will also influence deflection readings and this should be the same as for previous sets The dial gauge, or electronic measuring device, should be placed between the webs at the marked position with the crankpin set almost at Bottom Dead Centre (BDC) The dial gauge should be set to zero and the first position designated B1 The crankshaft is then turned and readings are taken when the crank is at 90° from the BDC position {reading 51},at Top Dead Centre (TDC) {reading T, at 90° after TDC {reading 52} and again near BDC with the crank on the other side of the connecting rod {reading B2}.An average reading for the bottom position is then obtained, B = 0.5(B1 + B2) In some cases, particularly for the aftermost units near the turning gear, engine builders recommend that turning should be stopped and the turning gear eased backwards slightly to take the tangential pressure off the turning gear teeth, as this pressure could cause 152 Engine Maintenance false readings The vertical deflection difference, V = (T - B) is compared with the table or graph issued by the engine builder and if it exceeds permissible limits realignment of the crankshaft is necessary This generally implies replacement of bearing shells for units adjacent to the crank but wear at these must be checked The chocks should be checked before any bearing adjustment takes place as loose holding down arrangements can influence deflections Deflection readings 51 and 52 are not used to indicate vertical alignment of the crankshaft but are taken for reference as they indicate horizontal misalignment and possible dial gauge defects Engine Maintenance 6.3.3 Bearing Inspection Thin shell main bearings can be removed from the engine for inspection or replacement Todo this the bearing cap must first be lifted to expose the upper shell which can then be removed The lower shell, however, is the one which takes the weight of the crankshaft and it is this shell which is likely to be worn or damaged making inspection essential In order to allow the lower shell to be removed the crankshaft must be lifted slightly and this is done hydraulically A crosspiece is located under the crankshaft webs at one side of the main bearing The ends of the crosspiece rest on the bedplate transverse girders, and hydraulic jacks on the crosspiece rise to touch the webs Hydraulic pressure applied to the jacks causes the crankshaft to lift, and the allowed lift corresponds to the clearance on the adjacent main bearings which has been measured using feeler gauges By means of wire ropes attached to the top of the shell, the shell can be rotated around the journal and removed Some engine manufacturers prefer the lower halves of bearing shells to be turned out rather than the crankshaft lifted It is essential to follow the manufacturer's instructions carefully as damage may result from malpractice Replacement of the shells should be carried out in the reverse order If the crankshaft has to be turned with the main bearing cap removed, to allow inspection of the journal, stops fitted over the bearing cap studs are used to prevent the lower shell from rotating Bearing and journal surfaces should be inspected for signs of cracking, corrosion, spark erosion, scuffing, wiping or scratching The back of the shell must also be inspected for signs of fretting and other damage 6.4 Connecting Rod Bearings Bottom end and crosshead bearings must be inspected for the same signs of damage which can be found at the main bearing It should be emphasised that in each case the bearing shell which can most easily be exposed is not the one subject to the greatest loading At the bottom end it is the upper shell which rests on the crankpin and is under load during service Dropping the lower cap allows the lower shell to be removed but to expose the upper shell it is necessary to support the crosshead and connecting rod assembly at the top of the piston stroke with stop screws, or similar, located below the guides The crankshaft can be rotated so that the crankpin is clear of the connecting rod The upper bearing shell and crankpin can then be inspected and the shells replaced if necessary For the crosshead bearing it is the lower shell which takes the load and this is exposed by turning the engine to TDC, removing the bearing caps, supporting the piston and crosshead pin on supports and 154 Engine Maintenance turning the engine so that the upper end of the connecting rod and bearings comes clear of the crosshead pin 6.4.1 Guide Clearance Piston misalignment results from wear at the guide shoes The guide bars are of hardened steel and therefore are unlikely to wear Because of the abundant supply of lubricant directed to the sliding surfaces of the guides wear is normally very minor and throughout their operating life most engines are unlikely to need any guide adjustment However, in engineering the unexpected can always happen and so the guide clearances should be checked whenever the crosshead is overhauled Ideally the ship should be on an even keel and perfectly upright The crankshaft is turned in the astern direction until the crank is about 45° after BDC so that the guide shoes rest against the ahead guide The guide shoes should have contact at the top and bottom of the guide bars Clearance between the lower part of the piston and the liner are checked in the fore and aft directions using long feeler gauges Clearance between the guide shoe and guide bar on the none contact face should be measured using feelers Clearances should also be measured between the fore and aft rubbing faces of the guide shoes and their mating guide bars as this indicates alignment in the fore and aft direction Adjustment can be done by removing and fitting shims as necessary, if possible, or by renewing the white metal if that is the only means available 6.5 Cylinder Inspection The condition of piston rings, piston and the liner can be checked through the scavenge ports either directly or with a mirror Cracking or other damage to rings can be readily observed and pressing the rings will indicate if any have a tendency to stick in their grooves Burning or carbon deposits on the crown are indicative of poor atomisation and subsequent poor combustion Carbon deposits may also form on the piston topland and in the spaces between the rings indicating serious problems with combustion or cylinder lubrication The liner surface may indicate abnormal wear patterns such as scuffing (micro seizure) and clover-leafing 6.5.1 Scuffing Scuffing is indicated by vertical streaks on the surface of the liner and the rings and can be at a small section of the liner or extend around the liner circumference It is caused by seizure on a microscopic scale due to inadequate lubrication, high spots on rings and the liner making contact 155 Engine Maintenance Engine Maintenance resulting in local seizure Due to the fact that the piston is moving the seized faces are immediately tom apart which causes damage to the contact points The ring and liner surfaces become hard and glassy and the scuffing spreads around the liner circumference as the rings rotate in their grooves Due to the state of the liner surface the cylinder oil supplied cannot key itself and run off, therefore, there is no effective oil film on the liner and the scuffing gets worse The solution is to replace the rings and liner, however, if the scuffing is only slight it is possible to recover the situation The rings can be replaced and the hard and glassy liner surface broken with a rough stone to provide a key for the cylinder oil Inadequate cylinder lubrication is invariably the cause of scuffing, therefore, it is essential for the cylinder lubricant supply be corrected in terms of quantity and quality 6.5.2 Piston Rings Whenever a piston is lifted the condition of the rings and their grooves must be assessed and the information recorded Under most circumstances pistons will only be lifted when there is a need for overhaul and ring replacement; it is not normal to refit old rings but if this is necessary the advice of the engine manufacturer should be sought Prior to fitting piston rings, including new rings, the rings grooves should be checked for damage such as corrosion and cracking The groove wear pattern should also be checked and the grooves faces should remain parallel, and more groove wear at the front means that the piston should be reconditioned The grooves must be cleaned and the rings tried in the grooves to check that the axial clearance is within limits Ring butts should be measured in an unworn part of the cylinder liner and filed if necessary to give the correct clearance Too small a butt clearance can result in rings jamming as they expand during service The spring of the rings should be checked as it is this spring which provides the initial sealing force between ring and liner After fitting the rings in their grooves, using the tool 156 6.5.4 Cylinder Liner Calibration (Figures 80 and 81.) Before calibrating the liner the calibration gauge and calibration micrometer should be at the same temperature as the cylinder liner The temperature should be recorded and a correction made to the readings after the calibration If the liner temperature exceeds that of the calibration micrometer the actual readings should be multiplied by the factor as below Temp Difference °C Factor 10 0.99988 20 0.99976 30 0.99964 40 0.99952 50 0.99940 Clover-leafing If the cylinder oil cannot neutralise the acid products of combustion corrosive wear will take place at the liner surface The location of greatest wear is between the quills caused by an inadequate spread of cylinder oil These wear regions enlarge and give a characteristic 'clover leaf' shape to the wear pattern Piston rings are unsupported by the liner surface where the corrosion has taken place and combustion gases can act on the faces of the rings resulting in ring collapse in extreme cases The solution to the problem is to ensure the correct grade of cylinder oil is used for the fuel oil being burnt, and that there is sufficient oil on all parts of the liner surface 6.5.3 provided, they should be checked to ensure they will move completely into the groove and that they have freedom once in the groove If there was a temperature difference between the liner and micrometer of 50°C and the measured liner bore was 761.5mm, the corrected value would be 761.5x 0.99940 = 761.043mm, a reduction of 0.457mm 6.5.4 Calibration Gauge The points at which liner readings are taken are chosen to give a picture of the liner wear and more readings are taken in the regions where the greatest wear is expected This is particularly the case at the top of the liner but additional readings may also be taken around the scavenge ports Readings are taken in the fore and aft direction and also in the port and starboard direction The use of a calibration gauge ensures micrometer readings are always taken in the same positions which allows for a true comparison with previous sets of readings 6.5.4.2 Calibration Results Calibration readings are recorded in tabular form and in some cases graphs of actual wear may be drawn The taking of readings fore and aft and port and starboard allows for ovality in the liner wear to be checked The maximum acceptable liner wear depends on the bore but lies between 0.4 per cent and 0.8 per cent of the initial bore, however, ovality can be a reason for replacing a 157 Engine Maintenance Engine Maintenance liner before maximum wear has been reached Higher wear in certain sections of a liner suffering from ovality allows gas to act on the face of the piston rings causing collapse 6.6 Cylinder Cover and Valves Although it is possible to assess the condition of the under face of the cylinder cover through the scavenge ports using a mirror it is much easier if the exhaust valve is removed Any burning is indicative of faulty atomisation This inspection should be done each time an exhaust valve is removed for 159 -Engine Maintenance Engine Maintenance overhaul The exhaust valve seating face should be checked prior to grinding as abnormal wear or damage will indicate defective cylinder operation which will result in damage to the overhauled valve Valves and their seats must be ground separately using the special rig A differential seating angle is provided as during service the exhaust valve will deform producing a full face contact When the exhaust valve is dismantled for overhaul the opportunity should be taken to inspect the air springing arrangement and the hydraulic actuating cylinder 6.6.1 Header missing Fuel injectors, air start valves and relief valves should be removed from the cylinder cover for overhaul at the recommended intervals The Functionality of fuel injectors and air start valves are checked whenever they operate, however, the relief valve only operates if there is excessive pressure in the cylinder and it may never seem to operate It should be overhauled at the recommended intervals as the build-up of carbon between the valve body and seat may actually prevent it from lifting 6.7 Chain Drive and Camshaft cleaning of the turbine and impeller cannot be undertaken so readily Intervals between cleaning of these parts will vary with operating conditions and the quality of fuel being burnt Fuel quality and the effectiveness of its combustion will influence the build-up of deposits on the turbine and nozzle rings while dust in the atmosphere will result in increased deposits on the impeller and air side of the turbocharger Manual cleaning of the air and gas sides of the turbocharger can be undertaken when the engine is stopped in port or for other maintenance but in-service cleaning can be carried out at particular intervals dictated by turbocharger performance An in-service cleaning programme should not be started if the turbocharger has not been cleaned by such a method for some time as heavy deposits may exist and the in-service cleaning may only partially remove these The result will be rotor imbalance and severe vibration Manual cleaning should be carried out before an in-service cleaning programme is initiated 6.8.1 The manufacturer's cleaning instructions should be followed at all times The turbine may be cleaned with water or by a dry method 6.8.1.1 Chain drives must be maintained at the correct tension at all times otherwise damage to the chain links and sprockets could Occur.Although the chain may have an automatic tensioning device it is essential that the device is correctly set As chain 'stretch' occurs the tensioning device will compensate and maintain tension but it cannot this indefinitely and it will eventually have to be reset Chain links should be inspected for cracking at the side plates and damage to the roller faces Rollers must always turn freely on their pins and bushes Sprockets are subject to wear at the teeth and this wear can be determined by placing a straight edge on the sprocket and measuring the distance between the straight edge and the sprocket face The running faces of carns and rollers should be completely smooth and bright, however, inadequate lubricant supply will cause scuffing As with the scuffing in cylinders it is essential that the lubrication situation is corrected otherwise serious damage can result 6.8 Turbocharger Cleaning The gas and air sides of turbochargers must be kept in a clean condition as a build-up of deposits can seriously impair the supply of combustion air to the engine and result in other problems such as turbocharger surging Suction filters can be removed for cleaning without disturbing engine operation but Gas Side Cleaning Turbine Dry Cleaning (Figure 82.) The interval between dry cleaning is about 24 to 50 hours and the procedure involves the injection of a specific quantity of crushed rice, walnut shells, or similar, into the gas flow entering the turbine nozzle ring Particle size should be about 1.5mm Cleaning is a mechanical impact process and maximum effect is obtained at high speed so it is important that engine and turbocharger speed is maintained Cleaning by this method should not be carried out with the engine operating below half load 6.8.1.2 Turbine Water Washing (Figure 83.) This is carried out every six days of engine operation depending upon operating conditions Engine load must be reduced below half power and atomised water is injected into the gas flow to the turbine nozzle ring The turbine casing drain must be open throughout the cleaning process to allow water and deposits to drain away A plate will normally be fitted to the turbocharger indicating the exact conditions under which water washing may be carried out The effectiveness of the cleaning process can be assessed by noting the amount of deposits in the water leaving the casing drain When the engineer is satisfied that the turbine is clean the water may be shut off, the casing drain closed when water flow ceases, and the engine load returned to normal over a half hour period 160 161 Engine Maintenance Engine Maintenance 6.8.2 Compressor Cleaning Cleaning of the impeller and volute casing is undertaken at intervals of between 25 and 75 hours A fixed quantity of water is injected into the eye of the impeller over a short period of time and the action of the water droplets remove light deposits from the impeller and casing surfaces There is no need to reduce speed during this procedure 6.8.3 Charge Air Cooler Cleaning (Figure 84.) Cleaning of the charge air cooler should only be undertaken when the engine is stopped as there is a risk, even when a water separator is fitted, of the cleaning fluid being blown into the cylinders and causing excessive liner wear Coolers are usually cleaned by means of a chemical agent which is sprayed over the outer surface of the cooling bank and reacts with the deposits on the surface of the finned tubes The polluted cleaning agent then returns to the storage tanks via a filter In the tanks, under the action of heat, the deposits settle out in the form of a sludge which can be removed from the tank The chemical cleaning agent may be used repeatedly until a test shows that it is no longer fit for further service and then the charge must be replaced 6.9 Jacket Cooling Water The jacket cooling water is chemically treated to prevent corrosion in the cooling system Leakage from the system is made-up with distilled water and so over a period of time the chemical concentration reduces Evaporation from the system also has to be made up but there is no chemical depletion due to evaporation Chemicals may also degrade as they react to prevent corrosion As protection against corrosion depends on the correct concentration of the inhibitor in the cooling system it is essential that the jacket water be tested each week and any deficiency corrected 6.10 System Oil Testing Properties of the engine oil such as the system lubricating oil, camshaft oil, turbocharger oil, and governor oil, change during service as the quality of the lubricant deteriorates due to oxidation and contamination It is essential that any oil used in the engine remains suitable for the purposes intended and frequent testing is the only way in which the engineer can know how effective the oil is Shipboard testing kits are available and these enable many of the oil's properties to be determined, however, a more thorough analysis can be obtained from a shore laboratory Samples must be taken of each oil used and 163 Engine Maintenance analysed either on board ship or ashore at intervals indicated by the engine builder and oil supplier The sampling and testing interval should not exceed three months and more frequent analysis is needed if previous testing indicates a possible problem Samples should be drawn from the oil circulation system and not from the bottom of the storage tank Index A Air cooler 81 Air springing 27, 28 Alkalinity 72 Astern guides Atomisation 52, 64 Axial damper 48 Axial vibration 48 B Balancing 93 Base number 73, 136 Bearing inspection 154 Bedplate 11, 12, 152 Bore cooling 18, 19, 21, 37 Box girder 12 Butt clearance 34 C Caged valve 22 Camshaft 5, 26, 50, 59, 60, 67-70, 95, 115, 128, 163 chain drive 51 gear drive 52 Carbon trumpets 62 Cermet 24 Chain stretch 52 Charge air cooler cleaning 163 Chocking 82 non-metallic 84 Clover-leafing 156 Coil springs 28 Connecting rod 3, 4, 9, 13, 38, 40, 4246, 93, 144, 152, 154 Constant speed gearing 106 Continuous slow running 141 Corrosion protection 71 Counterweights 95 Crank throw 9, 12 Crankcase explosion 15, 99-102 lubrication 15 relief valve 100, 101 Crankpin 42, 45, 46, 48, 152, 154 164 Crankshaft 1, 3, 7-11, 45-51, 70, 82, 91, 93, 95, 105-107, 116, 120, 129, 131, 134, 140, 144, 152, 154, 155 deflections 152 Critical speed 91 Crosshead 1, 3, 8, 32, 34, 40, 42-46, 58, 65, 70, 93, 133, 143, 155 bearings 40, 71, 154 pin 40 Cylinder block 15 Cylinder cover 1, 5, 15, 16, 20-22, 34, 61, 65, 76, 93, 143, 159, 160 Cylinder cut-out 141, 143 Cylinder inspection 155 Cylinder liner calibration 157 Cylinder lubrication 72, 73, 135 Cylinder power balance 131 Cylinder power calculation 109 Cylinder relief valve 29 D Deep section cylinder cover 20 Detachable seat 22, 23 Diagnostic systems 114 Diaphragm 1, 13, 15, 32, 38, 60, 72, 99-103, 144 E Electro-hydraulic governor 67 Electronic indicator systems 134 Emergency control 129 Emergency running 143 Emergency stopping 140 Engine cooling 76 Engine frame 10, 13, 15, 46 Engine management systems 112 Engine monitoring systems 107 Engine selection 116 space requirements 125 Engine start-up 129 Exhaust emissions 146, 147 Exhaust gas system 123 Exhaust valve 22 Expert systems 114 165 Index F Fatigue 10, 12, 15, 18, 28, 79, 85, 125, 145, 148, 152 Fir tree roots 78 Frames 13 Fuel injection 52 Fuel injector 61 cooling 63 Fuel pump 54 cam roller reversal 59 Fuel quality setting 58, 65 G Govenor 52, 55, 58, 65-70, 130, 132, 139 143, 163 actuator 68 malfunction 69 Guide bars 3, 4, 13, 40, 42, 52, 155 Guide clearance 155 Guide shoes 3, 4, 40, 42, 70, 155 Guides 4, 42 H Holding down studs 85 Holding down system 126 Hot spot 99-101 Hydraulic valve actuation 25 Hydrostatic lubrication 40 I Impeller 78-81, 110, 124, 137, 138, 144, 161, 163 Inconel 24 Indicator cock 30, 110 Indicator diagrams 110, 144 J Jacket cooling water 163 Jacket water treatment 76 l Labyrinth seal 79 Lacing wire 78 Lateral vibration 88 166 Layout diagram 116 Lead overlay 43 Load diagram 117-119 Long stroke engine 8, 12, 20, 73 Loop scavenging 5, Lubricating oil 71-75, 163 Lubricator quill 73, 144, 156 M Main bearing caps 45 Main bearings 152 Maintenance planning 114 Maintenance records 151 Molybdenum steel 24, 32 Moment compensator 95 N Nimonic 24 Noise 115 Non-metallic chocking 83, 85 o ring 16, 17, 24 Oil cooling 38 Oil mist detector 100 Orders of vibration 91 Overspeed trip 69 p Piston 1, 3-8, 15, 25, 28-40, 64, 6873, 128-140, 143, 154-158 cooling 35 Piston crown 21, 33, 35, 38, 64, 103 Piston ring 26, 32, 34, 40, 73, 128, 136, 137, 155-158 Piston rod 1, 3, 32, 33, 35, 38, 93, 103 Piston skirt 7, 32 Power take off 106 Power take-in 103 Primary crankcase explosion 100 Puncture valve 26, 55, 60, 129, 143 Index Resin chocks 86, 152 Reversing systems 58 Rocker operation 25 Rotocap 27 S Safety cutout 70 Scavenge fire 15, 99, 102 Scavenge ports 5-7, 35, 102, 135, 139, 155, 157, 159 Scavenge trunking 1, 103, 138 Scavenging 5, 7, 17, 35, 78, 122, 144 Scuffing 155 Secondary crankcase explosion 100 Servo-governor 66 Shaft earthing device 126 Sheathed pipe 25, 26, 59 Side chocks 86 Specific fuel oil consumption 9, 29, 64, 119 124, 134, 137 Speed droop 66 Spinner 24, 27 Static converter 107 Stellite 24 Stress raisers 10, 12 Stress relief 12 Stroke to bore ratio Supercharging System oil testing 163 T Tappet clearance 25 Thermal stability 72 Thermal stress 18 Thick shell bearing 42 Thin shell bearing 42 Thrust block 48, 50, 86, 99, 100 Thrust chocks 86 Tie rod 10, 45, 46, 93, 103 Tie rods 15 Top bracing 78 Topland 20, 33, 34, 155 Torsional vibration 48, 93, 95, 131 Torsionmeter 111 Trend analysis 113 Turbo compound system 120 Turbocharger 7, 76-81, 110-115, 117, 122-125, 137-140, 144, 145, 160-163 bearings 79 cleaning 160 failure 144 selection 124 surging 137, 139 two-stage 103 Turbo-compound system 105 Two-stroke cycle 4, 147 U Uniflow scavenging Unmanned machinery space 101, 102, 112, 131 V Valve rotation 26 Variable exhaust closing 29 Variable injection timing 55, 65 Vibration 48, 78, 79, 88, 91, 93, 95, 107, 114, 123, 125, 130, 132, 138, 143, 161 frequency 95 Vibration damping 49, 79, 95 Viscosity 72 W Water cooling 38, 124 Water separator 82 White metal 42-44, 79, 155 R Residual stress 60, 61 167 Shell Marine Products Premium Quality Lubricants, Fuels and Services for the Marine Industry World-wide Availability Shell is a supplier of marine fuels at over 400 convenient locations and marine lubricants at over 1,400 ports world-wide Premium Quality Products Shell supply high quality marine fuels and lubricants which give outstanding performance in shipboard equipment Innovative Technical Services Shell can help make your shipboard operations easier by providing specially developed technical and oil analysis services such as Shell RLA and Shell RLA OPICA Customer Service Friendly· customer service teams and representatives are ready and waiting to help you in over 20 countries Technical Support Experienced technical advisors are available to help you and can assist with any marine fuel or lubricant problem that you may have For more information about Shell's global marine service please visit our web site at http://www.shell.com/marine ... Cylinder Liner 2. 7 Cylinder Cover 2. 8 2. 9 2. 10 2. 11 2. 12 2.13 2. 14 2. 15 2. 16 2. 17 2. 18 2. 19 2. 20 2. 21 2. 22 2 .23 2. 24 2. 25 3.1 3 .2 3.3 Definition of a Low Speed Diesel Engine The Crosshead Engine The... Low Speed Diesel Engine 1.1 1 .2 1.3 1.4 1.5 1.6 Engine Construction 2. 1 Engine Structure 2. 2 Bedplate 2. 3 Frames 2. 4 Cylinder Block 2. 5 Tie Rods 2. 6 Cylinder Liner 2. 7 Cylinder Cover 2. 8 2. 9 2. 10... Earthing Device 116 122 123 124 124 125 126 126 4.1 4 .2 4.3 4.4 4.5 4.6 4.7 4.8 103 105 107 1 12 1 12 115 Engine Operation 5.1 5 .2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 6.1 6 .2 6.3 6.4 6.5 6.6 6.7