MARINE ENGINEERING PRACTICE Volume Part 17 SLOW SPEED DIESEL ENGINES by S H HENS HALL B.Sc(Eng) C.Eng F.LMar.E and G G JACKSON THE INSTITUTE OF MARINE ENGINEERS Published by The Institute of Marine Engineers The Memorial Building 76 Mark Lane London EC3R 7JN Copyright © 1978 The Institute of Marine Engineers A Charity registered in England and Wales Reg No 212992 Reprinted 1987 Reprinted 1993 Reprinted 1995 Reprinted 1996 Reprinted 1998 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form of by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher Enquiries should be addressed to The Institute of Marine Engineers ISBN: 900976 79 Printed in the United Kingdom by Hobbs the Printers Ltd, Brunei Road, Totton, Hampshire 5040 3WX CONTENTS l.Introduction Scavenging, charging and supercharging 2.1 Definition of terms 2.2 Provision of scavenging and charging air 2.3 Gas exchange processes 2.4 Turbocharging 2.5 Intercooling 2.6 Two-stage turbocharging Turbocharging, air filters and air coolers 3.1 General description 3.2 Lubrication system 3.3 Contamination and cleaning 3.4 Corrosion, erosion and other defects 3.5 Vibration Combustion and the diesel cycle 4.1 Chemical composition of fuels 4.2 Chemistry of combustion 4.3 Combustion in the diesel engine 4.4 The diesel cycle 4.5 The idealised cycle 4.6 Comparison of idealised and actual diagrams 4.7 Out of phase diagrams 4.8 Exhaust smoke Fuel injection systems and equipment 5.1 Types of fuel injection system 5.2 Jerk type fuel pumps 5.3 Common rail system fuel pump - Doxford 5.4 Fuel injection 5.5 Injection cycle and timing 5.6 Maintenance 5.7 5.8 Bearings 6.1 6.2 6.3, 6.4 6.5 6.6 6.7 Fuel pipes Injector testing Types of bearing and bearing metals Clearances Thrust bearings Oilways and grooves Overhauling and maintenance Bearing failures Bearing condition warning devices Lubrication, lubricating oils, systems and treatments 7.1 Duties of a diesel lubricant 7.2 Cylinder lubrication 7.3 Crankcase lubrication 7.4 Maintenance of crank chamber oil 7.5 Treatment of lubricating oil 7.6 Testing of lubricating oil 7.7 Cleaning lubricating oil system Fuel oil 8.1 8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.2.5 8.2.6 8.2.7 8.2.8 8.2.9 8.2.10 8.2.11 8.3 8.4 8.5 Origin and refining Properties of fuel oil Specific gravity or density Viscosity Calorific value Ignition temperature Flash point Ash Water Sulphur Conradson carbon residue Cetane number Grade of fuel oil Fuel oil system Purification of fuel oils Self-cleaning purifiers - automatic operation Fresh and sea water cooling systems 9.1 The need for cooling 9.2 Open and closed fresh water systems 9.3 Sea water system 9.4 Water pumps 9.5 Heat exchangers 9.6 Water treatment 10 Starting, 10.1 10.2 10.3 10.4 10.5 10.6 manoeuvring and speed control Starting Starting interlocks Starting air valve Compressed air for starting Speed regulation Engine governors 11 Brief description of some engines 11.1 Doxford - Figs 35 and 36 11.2 Sulzer - Figs 37 and 38 11.3 Burmeister & Wain - Fig 39 11.4 Grandi Motori Trieste (G.M.T.)-Fig 11.5 M.A.N - Figs 41, 42, 43 and 44 11.6 Mitsubishi - Figs 45 and 46 12 Preparing a diesel engine for running 13 Watch keeping duties at sea 14 Arrival at port 15 Overhauling in port 15.1 Safety precautions 15.2 Overhauling and servicing 16 Safety devices 17 Scavenge Fires 18 Crankcase explosions 40 LIST OF FIGURES Fig Fig Fig Fig Fig Forms of scavenging Engine and turbocharger system Sectional arrangement of turbocharger Two-Stage Turbocharging system (Mitsubishi) Lubricating oil system for turbocharger with plain bearings Fig Air side cleaning of intercooler Fig Indicator diagram Fig PV ideal diagram Fig Pressure - crank angle diagram Fig 10 Out of phase diagram Fig 11 Interpretation of out of phase diagrams Fig 12 Essential elements of jerk pump fuel injection system Fig 13 Essential elements of common rail fuel injection system Fig 14 Operation of jerk type Fuel Pump Fig 15 Jerk pump timing adjustment Fig 16 Fiat fuel pump Fig 17 Delivery valve (volume unloading) Fig 18 Delivery valve (pressure unloading) Fig 19 Common rail fuel injection pump Fig 20 Spill valve Fig 21 Fuel injector valve Fig 22 Needle valve seat Fig 23 Fuel injector needle lift diagram Fig 24 Shell type bearing Fig 25 Bridge gauge (for wear down) Fig 26 A typical lubricating oil system Fig 27 A typical fuel oil system Fig 28 Purifier bowl operation Fig 29 Fresh water system open Fig 30 Fresh water system closed Fig 31 Sea water system 11 12 17 20 22 23 24 27 28 29 31 32 33 33 34 36 37 38 40 44 46 57 63 66 71 71 73 Fig 32 Fig 33 Fig 34 Fig 35 Fig 36 Fig 37 Fig 38 Fig 39 Fig 40 Fig.41 Fig 42 Fig 43 Fig 44 Fig 45 Fig 46 Heat exchanger Air starting system Diagram of an hydraulic governor Sectional views of Doxford 'J' engine Doxford engine running gear Section of Sulzer engine type RND M Combustion space in Sulzer type RND M engine Section of B & W engine type K90GF Section GMT engine type B1060 M.AN engine frames and bedplate Section of M.A.N engine type KS2 90/160B M.AN cylinder liner M.AN cylinder cover and piston Section of Mitsubishi engine type 8UEC 85/180D Mitsubishi two-stage turbo charging system 74 77 80 83 85 87 89 91 93 94 95 96 97 99 101 INTRODUCTION Energy is derived from natural sources such as coal, gas and oil All release energy in the form of heat when united with oxygen by the process of combustion Other thermodynamic processes include compression, expansion, cooling, evaporation and condensation By combining certain of these processes and applying them to a working fluid, such as air or steam, cycles may be constructed which are capable of transforming heat energy into mechanical work One such basic cycle is that of the internal combution engine Internal combustion engines range in size from miniatures for model toy cars to 48,000 BHP giant diesel engines for marine propulsion With practical fuels, combustion is started by bringing them into contact with the oxygen in air and raising their temperature locally to the point of ignition In the familiar automobile engine the passage of a spark provides ignition In the diesel engine the charge of air in the cylinder is compressed to such a degree that its temperature is high enough to cause the fuel sprayed into the cylinder at the end of the compression stroke to ignite spontaneously This distinctive feature of his engine was described by Dr Rudolf Diesel in his patent of 1892 The essentials of the internal combustion cycle are compression of the working fluid (air), heating by combustion of the fuel in it and expansion converting heat energy into mechanical work The work done during expansion exceeds the work required for compression and the difference constitutes the power output of the engine The foregoing applies to all internal combustion engines, including gas turbines In the case of reciprocating engines a charge is taken into the cylinder and is compressed, ignited, and expanded there each cycle At the end of the expansion the spent charge is exhausted and replaced by a fresh charge If the processes of exchanging the spent charge for the fresh one are carried out by means of piston movement and mechanically operated valves the result is the well known four stroke cycle This consists of the following Intake of fresh charge as the piston moves out Compression as the piston moves in Combustion at inner dead centre, followed by expansion as the I MARINE ENGINEERING PRACTICE piston moves out Exhaust as the piston moves in If the gas exchange processes are carried out at the end of the expansion stroke and the beginning of the compression stroke by means of ports uncovered by the piston, sometimes in combination with mechanically operated valves, the result is the equally well known two stroke cycle Considerations of the gas exchange processes in most designs of twostroke cycle engines tend to favour a relatively long stroke in proportion to the bore Such a configuration also suits the low rotational speed which is required of a direct-coupled engine if the propeller is to be efficient In consequence, modern large marine diesel engines, almost without exception, operate on the two-stroke cycle principle J 2.1 SCAVENGING, CHARGING, AND SUPERCHARGING DEFINITION OF TERMS Scavenging is the process by which the spent charge, or the remnants of it, are displaced from the cylinder by fresh air blown through it Charging is the process by which the cylinder is filled with air at the beginning of the compression stroke Supercharging is a process or combination of processes whereby the density of the charge is increased to provide a greater mass of air in the cylinder in which a correspondingly larger amount of fuel can be burned, so increasing the power output of the engine It should be noted that supercharging is not simply a matter of adding equipment to nonsupercharged engines The supercharged engine must be designed to withstand the increased pressures and thermal loads which result 2.2 PROVISION OF SCAVENGING AND CHARGING AIR It is essential to the scavenging process that the air entering the cylinder is at a higher pressure than the gas in the exhaust manifold Scavenge air is supplied to large diesel engine cylinders in a variety of ways The following methods have been used (a) (b) (c) (d) By direct driven reciprocating scavenge pumps, usually connected by quadrants, or by links and levers to the crosshead bearing Positive displacement rotary blowers have also been used, usually gear driven and sometimes chain driven By exhaust gas turbochargers in the case of supercharged engines These may be alone or assisted at low revolutions by an auxiliary fan By turbochargers in series with single or multiple reciprocating pumps By turbochargers in parallel with single or multiple reciprocating pumps The arrangements of the pistons, the ports they control, and the valves, together with the resulting path taken by the scavenge air, characterise the different types of two-stroke cycle engine The following engine types are in general use Opposed piston engines in which each cylinder has a piston at each · PREPARING A DIESEL ENGINE FOR RUNNING 103 incomplete combustion results There is also the danger of abnormally high pressures in the fuel line which result in fuel relief valves lifting and probable resultant damage to valve seats and other components (8) If hoppers or sight glasses are fitted check that there is an adequate flow of coolant through each piston, cylinder, cylinder jacket, turbocharger casing and injector (9) Check that the level of oil in the turbochargers is correct (10) Check that any vents in the systems are clear to allow the free flow of air from the cylinder cooling passages and turbochargers The charge air coolers should also be vented Unvented spaces encourage the formation of steam, corrosion, erosion and local overheating (I1) Check through the crankcase, etc for any tools, obstructions, or waste material and remove same The presence of any unwanted impedimenta could have serious consequences when starting and running the engine (12) Ensure that starting and control air valves are shut off and if necessary drain the systems Engage the turning gear (13) Ensure that the control linkage is lubricated and easily operated Prime the cylinder lubricators and ensure their tanks are kept at working level Check the pressures in the lubricating oil systems Open the cylinder indicator cocks to atmosphere, start up the turning gear and check that the lubricating oil is flowing freely from all running gear bearings If the turbocharger does not have its own selfcontained lubricating system check the flow controls (I4) Whilst the engine is being turned by means of the turning gear, the cylinder lubricators should be operated by hand at regular intervals (15) Engines with entablatures or scavenge air receivers should have the scavenge drains cracked open The drains from diaphragm glands should be slightly open (16) Check the engine room telegraph for proper functioning and at the same time check the telephones to the bridge and Chief Engineer's office (17) Check the auto-shut-down devices on the appropriate systems also the low pressure alarm devices for each system to ascertain that they operate at the correct settings (18) Where fitted, check the running direction safety interlocks for both ahead and astern running (18) Where fitted, check the reversing servo-motors for correct functioning (I9) Where fitted, check the running direction safety interlocks for both ahead and astern running (20) Prime the fuel pumps, fuel pressure pipes and vent the injectors (21) Check the pressures in the starting air tanks (22) Open shut-off valve for starting air tank, ensure that the automatic starting air valve has been set properly Close the drain valve on the 104 MARINE ENGINEERING PRACTICE starting air manifold (23) Turn on control air to all systems (24) Check and, if necessary, adjust oil, water and fuel pressures and temperatures (25) Disengage the turning gear and secure the operating lever (26) Switch the controls on the auxiliary blower to the automatic position and start the fuel booster pump (27) Inform bridge that engineroom would like to turn engine over slowly on air On engines with bridge control the control selector must be turned to the desired position (28) Close all indicating cocks (29) Report to the bridge when the engine is ready for stand-by (30) The oil mist detector alarm function can be checked according to the maker's instructions 13 WATCHKEEPING DUTIES AT SEA Constant inspection is a precaution which contributes to avoiding [rouble and the following routines must be carried out at regular intervals under normal operating conditions: (1) Regularly check and record all pressures and temperatures and enter same in the engineroom log Adherence to differentials in temperature and pressure limits is very important If a temperature or pressure is in doubt it should be checked against another instrument, a rough gude to temperature is by the feel of the hand (2) Due consideration must be given to engine speed and to the conditions of the loading of the ship and to the cleanliness of the hull when performance and records of the engine are being assessed Shop test reports and instruction manuals are a reliable reference and must be treated as such All records are important but particular attention must be made to turbocharger revolutions, scavenge air receiver pressures and temperature, and cylinder exhaust gas temperatures Consideration must be given to the calorific value of the fuel when assessing the daily fuel consumption (3) Check that the control valves for the cooling and lubricating systems are set properly If there is insufficient pressure in any system then the safety device alarm will be accelerated and the engine stopped All excessive pressure drops must be checked (4) Adjustments must be made to bring any abnormally high or low temperatures to within the prescribed range but this must be attained gradually Abrupt temperature changes can increase thermal stress and may cause trouble Check the air temperature after the charger air cooler This temperature should be as low as possible, a high temperature results in less oxygen being available for combustion and increased fuel consumption as well as higher exhaust gas temperatures An ideal temperature differential between the sea water inlet to the air cooler and the air outlet from the cooler is about 17'C (5) Care must be taken, in climates with a high humidity, that the temperature of the scavenge air is, if possible, kept above the dew point, otherwise condensation will form in the air receiver and the drain will require to be cracked open to avoid rust formation When water is apparent in the air receiver then a check must be made to verify whether it is sea water or fresh water; if it is sea water then the 105 106 MARINE ENGINEERING PRACTICE cooler is leaking and rectification is required (6) Drain scavenge space and jacket drains, also piston rod glands if there is an excess leakage of lubricating oil from the gland, then the scraper and sealing rings should be attended to at the first opportunity (7) Check, and if necessary, adjust the rate of feed of the cylinder lubricators (8) Check the temperature of the crank case doors by hand (9) Ensure that the fuel in the daily service tanks has been properly cleaned and that water and sludge have been drained off Drain sludge from fuel filters and purifiers (10) When burning heavy fuel ensure that there is sufficient heat available to bring the viscosity of the fuel to within the prescribed limits (10 Ensure that vents from cooling water spaces are kept open to permit air to escape (12) Check the pressure drop across fuel and lubrication oil filters Turn all manually operated filters and check that automatic filters are operating satisfactorily, drain sludge if necessary (13) Check the pressure drop across the charge air coolers for both sea and air pressure (14) Check oil levels in governor and other auxiliary equipment (15) Check all high pressure fuel lines for any signs ofleakage (16) Check camshafts, fuel pump bearings and other small bearings for temperature increase using the palm of the hand (17) Examine jacket, piston and fuel injector cooling water returns for any signs of contamination, any fouling must be investigated and rectified (18) Check air starting pipe to each cylinder, if overheating is discovered engine must be stopped, starting air valve and flame trap examined and replaced as necessary (19) Inspect access doors and thrust block aft seal for any signs of leakage (20) Check oil level in main engine lubricating oil drain tank (20 Check water level in jacket water cooling tank (22) Check levels in fuel tanks, cylinder lubricating oil and turbocharger lubricating oil header tanks (23) Drain off water from starting air tanks and top up pressure if necessary (24) Check lubricating oil samples as necessary and check operation of centrifuges (25) Record revolutions of engine over total watchkeeping period (26) Take indicator diagrams to check power and pressure in cylinders (27) Open drain valve on starting air manifold to check that valves in the system are tight (28) Water wash turbochargers as necessary (29) Clean air coolers at recommended intervals 14 ARRIVAL AT PORT If the ship is to be in port for a few days the following action is to be taken for the shut-down of services:(1) Ensure that the telegraph is at stop, the fuel control or speed adjusting lever is at zero and the starting air lever is in the neutral position (2) Shut the starting air valves and the starting air tanks, close the automatic starting air valve and, if fitted, isolate control air to the engine (3) Open drain cocks on the starting air manifold and any venting connections and ensure that there is no pressure anywhere in the starting air line The fuel booster pump and steam to fuel heater and strainer, together with the fuel pipe heater tracer lines should be shut off as soon as the 'finished with engines' order is acknowledged (4) Engage the turning gear and lock the lever Open the indicator cocks (5) By-pass the jacket water and lubricating oil coolers and continue circulating the coolants over the recommended period to allow the engine to cool down to an even temperature equal to the inlet temperature of the cooling water The main engine should be turned through one revolution at intervals during cooling and the cylinder lubricators should be operated by hand during the turning (6) Open all drain cocks of the scavenge air receiver, diaphragm glands and scavenge spaces (7) Ensure that the fuel pressure is at zero (8) Shut down the lubricating oil pump and open up crankcase for running gear inspection (9) Close all valves on the daily ready use fuel tank (10) Open the drains in the exhaust gas system (11) If in port for only a few days, keep the cooling water circulating at near normal temperature (utilising either a heating system or the heat of the cooling systems from the auxiliary engines) (12) At regular intervals the engine should be turned over by the turning gear with the indicator cocks open and the lubricating oil pumps in operation In high humidity climates the engine should be turned over twice a day (13) Any adjustments needed to improve efficiency noted during the previous voyage to be carried out 107 108 MARINE ENGINEERING PRACTICE (14) Leaks and/or any damage noted during the preceding inspection to be corrected (IS) Spare gear and the stores to be checked, including consumption of all lubricating and fuel oils and other consumables Replacements are, if necessary, to be requisitioned (16) If the engine is to remain idle for several weeks it must be given an extra cleaning and all bright parts suitably protected against corrosion The cylinder liners and pistons should be thoroughly oiled This could be achieved by turning the engine with the turning gear and operating the cylinder lubricators by hand Should the auxiliary engines and boiler be put out of action and there is a danger of frost then the water cooling systems should be thoroughly drained Piston rods to be liberally oiled (17) Chemically clean charge air coolers (I8) Turbocharger air filters to be inspected and if necessary washed in a bath of paraffin and then thoroughly dried before reassembly 15 OVERHAULING IN PORT 15.1 SAFETYPRECAUTiONS:There are certain basic rules to be followed when overhauling or repairing the main engine and these are as follows:(I) Close the starting air valves on the air storage tanks and open all drain valves on the air manifold (2) Ensure that the turning gear is engaged and secure the operating lever before entering the crankcase and carrying out work on any running gear parts (3) Before turning the engine by means of a turning gear make sure that there are no obstructions in way of the running gear and that the indicator cocks are open and stay open as long as any overhauling work is being carried out (4) Ensure that the cover provided is placed over the open cylinder when a piston has been removed (5) Always use adequate (weighted) lifting gear and check its condition before use Periodically check the brake in the electrical crane (6) Stand clear of any parts during lifting by crane (7) Ensure that power and light cables are kept free and not trapped in doors or under loads (8) Ensure that all ladders and walk ways are free of oil, grease and loose nuts, bolts, lifting equipment etc (9) Make sure that fire extinguishers are always topped up and ready for use (10) Never use an unguarded light to inspect an air vessel, fuel tank, lubricating oil tanks, air pipe, fuel pipe, crankchamber, or any part of the engine whatsoever (I I) If the engine has been stopped on account of overheating then the appropriate action as outlined in section 18 must be taken (12) If CO2 or any other method of extinguishing has been used in the crankcase or scavenge space then these must be very thoroughly vented before anyone is allowed to walk inside 5.2 OVERHAULING ANDSERVICING (I) Every piece of machinery must be overhauled and cleaned at regular intervals so that it is constantly in good running order All engine builders supply guidance and advice as to the intervals at which 109 110 MARINE ENGINEERING PRACTICE servicing should be carried out, this depends to a great extent on the power loading of the engine (2) Classification Societies have their own rules regarding major service and continuous service and adherence to these rules is vital (3) One of the factors which determines the frequency of overhaul is the load at which the engine operates in service as well as the grade of fuel and lubricating oil used (4) Before starting any overhauling it is important to check that the proper tools are available and that they are in good working order The use of wrong or worn tools can cause damage, loss of valuable time and injury to personnel Ensure that the starting air is off and that the turning gear is engaged (5) The Instruction Manual must be available to and thoroughly read by all engineroom personnel involved in maintenance and the recommended procedures should be followed (6) Before shutting down the lubricating oil pump check that the oil is flowing freely from the crosshead and other bearings, any interruption of flow may mean that the bearing metal is squeezed Open up crankcase for full running gear and crankcase inspection A sample of the lubricating oil should be taken and sent to the suppliers for analysis (7) Examine all lubricating oil and fuel oil filter elements for signs of damage (8) Drain cocks on turbochargers to be opened Inspection covers opened up and turbine wheels and nozzles examined for deposits If records show that the air flow is reduced then the protection grids must be opened up and cleaned (9) Clean scavenge air receiver and all scavenge drain connections Turn engine and examine piston rods and the piston rings through the scavenge ports, check rings for freedom of movement and whether intact During this inspection, cooling water and/or oil should be circulated for leakage examination (10) If required bridge gauge readings of main bearings and crankshaft deflections may be taken These records should be taken when the ship is afloat (11) All bolts and nuts in the crankcase to be checked for tightness and locking plates examined Main engine holding down bolts and main tie bolts to be checked for tightness All main nuts to be tightened to recommended torque values (12) When chains are fitted for camshaft drive the tension to be checked and guide bars and bearings examined, sprocket wheels to be examined for wear (13) The control mechanism should be checked for movement and the pistons of the pneumatic or hydraulic cylinders operated by hand to ensure freedom, ball ends and bearings examined and greased On completion of this work the whole of the control system to be OVERHAULING IN PORT III checked for proper functioning (14) Lubricating oil drain tank should be pumped out and cleaned of all sludge and gritty material Prior to carrying out this work the dirty lubricating oil tank should also be examined and cleaned if necessary (15) Check the operation of cylinder starting air valves, the master valve and other ancillary equipment, lubricate as necessary Check starting air pipe couplings and joints Air leaks in control systems are not always obvious and should be given extra care, loose couplings can cause starting failures (16) Operate cylinder lubricators by hand to ensure that the whole system has been primed and is functional, check that pipes, couplings and valves not leak (17) Relief valves, including those fitted on the crankcase, to be checked and overhauled as necessary (18) Ensure that oil changes for the governor and other ancillary equipment is carried out at the appropriate time (19) All dismantling work should be carried out with the greatest of care, all parts should be examined and cleaned as they are being removed Seal all openings against the ingress of dirt by means of sheet jointing or wooden blocks Do not use rags for this purpose (20) Do not use cotton waste for cleaning engine parts (21) Take great care to protect bearing surfaces, and screw threads etc., from damage and dirt (22) If any component is filed or scraped make sure that all residue is removed and that adjacent parts have been covered before work is commenced (23) All components overhauled during maintenance work must be checked for correct functioning before being put into operation in the engine Pipes must be pressure tested for possible leaks (24) The clearance of all essential parts is to be checked against the makers instruction manuals Parts outside prescribed limits are to be replaced from the spare gear or re-adjusted to give the correct clearance (25) Replaced parts should, if possible, be repaired and put into spare gear stock If this is not possible the parts should be re-ordered to maintain an adequate level of spares similar to that when the engine was commissioned (26) All spare parts should be examined at regular intervals and protective coatings be renewed as necessary to prevent corrosion or other damage (27) Synthetic rubber seals should be stored flat in a closed box and kept in as cool a place as possible (28) After completion of the overhauling, the engine must be thoroughly cleaned using cloths and not cotton waste (29) All tools must be assembled, cleaned and checked, and replaced in their proper positions Damaged tools must be replaced 16 SAFETY DEVICES Every large marine diesel engine manufactured is fitted with certain safety devices and most of these are listed hereunder: (1) Relief valve fitted to the combustion chamber to warn of excessive increase in combustion pressure (2) Relief valves fitted to the crankcase to act as safety valves should oil vapour ignite due, for instance, to a hot bearing (3) Relief valves fitted to scavenge spaces to protect the chamber against high pressure (4) Relief valves for fuel pumps and fuel systems to prevent high pressure lines from bursting (5) Relief valves for starting air system to prevent excessive pressures and flame traps or bursting discs at each starting air valve (6) Interlocks fitted to turning gear to ensure that the engine cannot be started whilst the turning gear is engaged (7) Automatic shut-down of the engine due to low pressure in the lubricating or cooling systems (8) Automatic shut down of the engine due to high or low temperatures in various systems (9) Shut down of the engine from the bridge should communications with the engineroom fail when the vessel is in a hazardous position (10) Over-speed trip which cuts the fuel supply to the engine should the main governor fail and the engine rev/min increases (1I) Oil mist detector fitted in the crankcase to give warning of hot running parts (12) A temperature probe system fitted to bearings to give an alarm of excessive temperatures (13) A temperature probe system fitted in the scavenge air space to indicate scavenge fires 112 17 (0 (2) (3) (4) (5) (6) (7) (8) (9) SCAVENGE FIRES The main cause of fouling of scavenge spaces is the blow-by of the products of incomplete combustion past the pistons and through the scavenge ports into the air chambers Under normal operating conditions this fouling is very slight and can be seen as a very thin oily film If combustion is poor due to the lack of proper fuel treatment, high viscosity fuel and neglect of maintenance on the fuel injection equipment, jamming of the piston rings will occur A further result will be an accumulation of fuel residue mixed with cylinder oil and these will be blown into the scavenge space Accumulation of such mixtures can be set alight by sparks or flame blow-by When fire has broken out the scavenge air temperature and the exhaust gas temperature after the cylinder in question will increase considerably and in some cases the turbocharger may start surging When alarm has been given, the speed of the engine should be reduced to slow and fuel cut off to the particular cylinder The cylinder oil supply should be maintained or even increased The bridge must be informed and permission to stop requested Cut out fuel priming pump Personnel must keep clear from doors and relief valves Where fire-fighting equipment is fitted to the air receiver this should be brought into operation as soon as possible If no equipment is available the fire will generally subside in about five to fifteen minutes Do not open scavenge space doors or crankcase doors before the site of the fire has cooled down When opening up care must be taken to keep clear of any flame After opening up all scavenge spaces must be thoroughly cleaned and all debris removed The piston rods and cylinder liner should be examined for surface blemishes, straightness etc., and the diaphragm glands examined to ensure that they are operational and not damaged If possible the piston head in question should be renewed at the earliest possible moment and the damaged unit overhauled On engines fitted with tie bolts it may be necessary to re-tighten the bolts adjacent to the fire The flat surfaces of the scavenge space should be examined for 113 114 MARINE ENGINEERING PRACTICE distortion as alignment of the camshaft bearings and the cylinder liners etc may be affected (10) When starting the engine again care must be taken after switching on the fuel to the cylinder in question that the cylinder lubricating oil quantities are reduced to normal Due to the large volume of air being blown through the receiver the formation of an explosive gas/air mixture is extremely improbable (11) Conscientious maintenance of the engine and regular inspection and cleaning of the scavenge air spaces will help to eliminate scavenge fires 18 CRANKCASE EXPLOSIONS (1) Spontaneous combustion of an oil mist in the crankcase of an internal combustion engine is a theoretical and practical impossibility There must always be an additional factor to start ignition and this is, in general, a very hot component Blow-by past the pistons due to badly worn or broken piston rings has also contributed to this hazard in engines without a diaphragm Records show that practically every part of the running gear of a diesel engine has at some time or another been responsible for a crankcase explosion (2) Experiment has shown that an SAE.30 lubricating oil will generate an oil vapour at approximately 200"C and research has discovered that there are two temperature regions which are conducive to ignition The lower region being between 270 & 350"C and the higher region at 400°C It has also been discovered that a minimum oil mist concentration of 50 milligrams per litre of crankcase volume is necessary to produce an explosive mixture (3) Relief valves have proved their worth in dealing with minor crankcase explosions Good maintenance, careful inspection and very definite action in cases of danger can to a large degree eliminate the danger of explosion (4) A mist generation of very low concentration is associated with the normal running conditions of a diesel engine and is due to the vapourisation of the lubricating oil at normal running temperatures The oil formations should never be mechanically exhausted as fresh air will flow in and this contains one of the main mediums of ignition - oxygen Should the crankcase be fitted with a vent pipe, this pipe must be fitted with some means to stop the ingress of fresh air (5) In an endeavour to avoid the risk of explosion this may be achieved if an early warning is given on the formation of oil mist before it reaches dangerous concentration on the crankcase (6) An oil mist detector has been designed by Graviner in collaboration with the British Ship Research Association and this unit operates photo-electrically and measures very small increases in oil mist density over and above that normally associated with the speed and load of the engine at any given time The detector operates on a principle of measuring the degree of mist density by observation of 115 116 MARINE ENGINEERING PRACTICE light on one of two cells normally in electrical balance The detector can locate hot spots or the incipient seizure of bearings or other working surfaces within the crankcase before serious damage occurs The unit monitors each crankcase and/or component such as chain case, in turn and on the detection of a hot spot visual warning is given by a red lamp and audibly by a Klaxon The location of the trouble is shown by a rotating valve position indicator which automatically stops when the alarm is given This indicates the source of the abnormal oil mist concentration (7) There are two types of detector, the comparitor type uses an average oil mist density as a datum, whereby a sample from each source is checked in turn against the combined mist from the remaining sources, plus a measurement of the average oil mist density against clear air once per cycle (8) The level type has the same sampling sequence but uses clear air as the datum for measuring (9) Other systems have evolved to give early warning of trouble in the crankcase and these are of the bearing temperature sensing type The advantage of this type of unit is that it can be extended to include thrust, line shaft and propeller shaft bearings Also the range of the temperature sensors are such that the whole unit can be extended to cover every part of the system of the engine from the lubricating oil drain tank to the exhaust gas outlet from the boilers The advantage of this system is that it maintains a continuous surveillance of operating conditions of the ship's machinery and it can monitor and relay information and give immediate visual and audible warnings of abnormalities Generally, the units are constructed on the modular principle which allows maintenance to be carried out from the front of the console and each module is self-contained in that if a fault develops a replacement module can be fitted at once When alarm set points have been adjusted in the new modules the system is fully operational (l0) The sensors on the main engine are so arranged that they either record the temperature of the bearing directly such as the main bearing and thrust, or they sense the temperature from the oil that is spilled from the bearings into troughs, for example, top and bottom end bearing and slipper bars (1 I) With this system a general alarm can be supplied remote from the main console such as on the bridge during unmanned conditions and in the Chief Engineer's office (12) When an alarm sounds the engine speed must be reduced to slow and the bridge informed and permission be obtained to stop the engine (13) When an engine has been stopped because of alarm conditions, under no circumstances must any doors or inspection windows be opened Oil should continue to be circulated and time allowed for the hot CRANKCASE EXPLOSIONS 117 components to cool down The early opening of doors allows an ingress of fresh air which can cause an explosion During the cooling down period the engineroom staff must keep clear of the side of the engine which is fitted with explosion doors (14) After a period of at least 20 minutes, stop lubricating oil pumps, cut off all air and engage the turning gear The access doors should be opened and personnel must keep clear of possible flames Under no circumstances must naked lights be used nor should anyone be permitted to smoke (15) Examination should then take place for squeezed out bearing metal or loose bearing metal in the crankcase Heat discolouration of metal parts or blistering of paintwork must be investigated The ceiling of the crankcase and guide bars should also be observed If the crankcase is clear the camshaft drive and the main thrust should be inspected for signs of overheating (16) Should any damage be found, then a permanent repair must be put in hand immediately After the repair the lubricating oil system should be started and examined for free flow With all systems operational the engine should be started normally and run for 15 minutes at slow speed, then stopped and the appropriate surfaces felt for heating and observed for the formation of mist If all is clear then the engine should be run for an hour at half-speed and the safety precautions repeated If all is again well, increase speed to full and run for one hour and repeat the inspection process (17) On installations which have fire extinguishing equipment built in either to the scavenge space or crank space, the areas which indicate a threat of explosion should be immediately flooded In the absence of a total flood and extinguishing system, hand extinguishers should be at the ready when the crankcase doors are eventually opened Varying times have been quoted for the cooling down period and no set rules are available but the longer the time taken the greater the safety factor ... O2 CO2 + 393.8 MJ/kmol 2H2 + O2 2H20 + 26 1.06 MJ/kmol (With the liquid at 2S'C) The combined proportions by weight are obtained by considering the molecular weights H2 = 2; C = 12; O2 = 32. .. operation Fig 29 Fresh water system open Fig 30 Fresh water system closed Fig 31 Sea water system 11 12 17 20 22 23 24 27 28 29 31 32 33 33 34 36 37 38 40 44 46 57 63 66 71 71 73 Fig 32 Fig 33 Fig... lubricating oil 7.7 Cleaning lubricating oil system Fuel oil 8.1 8 .2 8 .2. 1 8 .2. 2 8 .2. 3 8 .2. 4 8 .2. 5 8 .2. 6 8 .2. 7 8 .2. 8 8 .2. 9 8 .2. 10 8 .2. 11 8.3 8.4 8.5 Origin and refining Properties of fuel oil Specific