11_Reversing of Two Stroke Engine

REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers

REVERSING OF TWO-STROKE ENGINE

CONTENTS 

INTRODUCTION

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ROTATION OF ENGINE IN REVERSE DIRECTION



LOST MOTION

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AXIAL SHIFTING OF CAMS

ROLLERS DISPLACEMENT 

CRASH ASTERN

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EMERGENCY CONTROL

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INTERLOCKS AND BLOCKING DEVICES

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TIMING ARRANGEMENT FOR DISTRIBUTOR

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REGULATORY BODY REQUIREMENTS FOR A REVERSIBLE

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AUTOMATION IN REVERSING

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BRIDGE CONTROL OF DIRECT DRIVE DIESEL ENGINE

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MAINTENANCE AND TROUBLESHOOTING

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ELECTRONIC OPERATION



PROGRAM CONTROL

INTRODUCTION Modern large two stroke marine engines with fixed pitch propeller directly coupled are required to be reversed, that is change in direction of rotation of engine is to be accomplished to move ship in ahead and astern direction. This is normally required during manoeuvring of ship, while berthing, passing through canals, lock gates, and anchoring etc. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers Direct reversing of engine however can be eliminated by fitting gearbox/clutch arrangement or by CPP (controllable pitch propeller), where pitch of the propeller blades is changed to achieve the propeller thrust in desired direction. Here unidirectional engines normally four stroke are preferred with this arrangement. Amount of air bottle volume required is also small in this case and once engine is started it need not be stopped during manoeuvring, hence danger of engine not starting in critical/emergency position also is eliminated. However large two stroke engines directly coupled to fixed pitch propeller are found to be most suitable for ocean going vessels. Advantages of this engines have, are more endurance due to less stresses, and time between overhaul is also more. However manoeuvring in these engines is critical operation, where all engineers have to familiarise with the system on vessel and should be able to change over the controls from remote station to local controls in case of failure of remote control system.

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ROTATION OF ENGINE IN THE REVERSE/OPPOSITE DIRECTION In order to make it possible for reverse rotation of the engine, the firing sequence is changed. This changes in firing order is only possible if we change certain parameters/timings of the engine as listed below. Starting air timing (Distributor). Fuel injection timing. Exhaust valve-opening timing. Starting Air Timing (Distributor)  Compressed air known as starting air at a pressure of 15 to 30 bar is used to crank the engine, to achieve a certain minimum revolutions for the fuel to be injected at correct compression pressure.  To achieve this cranking, compressed air is introduced in to the cylinders as per the firing order in the direction of rotation for the engine, which is controlled from starting air distributor timing, which is changed to reverse direction of rotation of engine.  Starting air distributor controls operation of starting valves fitted to each engine cylinder. Fuel Injection Timing  For a marine diesel engine to run, fuel is to be introduced in the cylinders in an atomised state as per the firing sequence. Fuel pump and injectors achieve all this successfully.  Hence fuel cam timings with respect to crankshaft is required to be changed to run engine on fuel at correct timing by fuel pump in both directions.

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Exhaust Valve Opening Timing In marine diesel engines, we find two type of arrangement. Scavenge and exhaust ports and Scavenge port and exhaust valve. Scavenge and exhaust ports (loop &cross): Here since piston governs the opening and closing of ports, the timing of these cannot be changed. Scavenge ports and exhaust valve: Here the piston governs the opening and closing of scavenge port, but since the exhaust valve is operated either mechanically or electronically its timing can be changed. Mechanically operated exhaust valve: An exhaust valve cam are present for operation of hydraulic pump which pressures the hydraulic oil, which acts on a piston to operate the exhaust valve. Hence lost motion or axial shifting of cams changes camshaft timing of these cams. However in some engines, this process is also eliminated in case of exhaust valve timing since it Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers is not important to run engine very efficiently in astern direction. This case is employed in MAN B&W S/L MC engines. In case of camshaft less modern engines timing of exhaust valve can be conveniently operated with electronic control of solenoid valves. METHODS OF CHANGING TIMINGS Large two stroke engines can be reversed by changing timing of camshaft, which can be done normally by the following ways. LOST MOTION (SULZER Engine) An engine reversing is carried out by circumferential translation of the camshaft relative to the engine crankshaft. This circumferential movement is accomplished by the use of a servomotor, in the camshaft gear wheel forming the camshaft drive. The servomotor consists of a pair of vanes, fitted on the camshaft, which moves between another pair of vanes fitted within the gear wheel rim. By putting lubricating oil under pressure between opposite pairs of vanes the camshaft is moved relative to the gear wheel and the engine crankshaft. This relative movement changes the timing for ahead and astern cylinders. By changing the position of cam on camshaft relative to crankshaft. A valve controls the oil flow to the servomotor, is actuated through a pneumatically controlled valve forming part of engine control system. The reversing angle (98) is so chosen that the same fuel timing in relation to TDC of the piston be obtained both in the ahead and astern direction. The distributor cam is also turns the same time being engaged with fuel camshaft rotation with bevel gears. Control slide valve Input to interlock devices Interlock signal Lube Oil Servomotor LOST MOTION (Rotary valve) To M/E crankcase drain

Servomotor (fuel distributor)

Telegraph

Reversing control valve Operated by telegraph LO from M/E crosshead Cut out servomotor

hydraulic blocking Device

Camshaft Lost Motion (working principles) Servomotors achieve the relative shifting of camshaft with respect to crankshaft. These servomotors are operated hydraulically. The oil is taken from the engine lube. Oil system (crosshead lube. oil. line) and goes to a reversing control valve, which is operated by the telegraph. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers This reversing control valve directs the lube. Oil to the servomotor chamber formed between the vanes for ahead or astern position as governed by the telegraph. The lube Oil after rotating the vanes in the servomotor goes to a control slide valve, which gives a hydraulic signal to the hydraulic blocking device. The hydraulic blocking device blocks the starting lever in stop position while reversing is taking place. It is only released when the vanes have shifted within the servomotor. And secondly sends a signal to cut out servomotor to prevent fuel supply to the engine in case of reversing has to taken place. When the engine starts, the direction of rotation is cross-checked by the rotation direction interlock, which takes input from the camshaft and lube. Oil taken from the lube. Oil line between the reversing control valve and servomotor. Whenever the direction is wrong, it sends a hydraulic signal to the cut out servomotor, which cuts the fuel to the engine, thus preventing engine running. Whenever the telegraph position is in stop position, the lube. Oil in the servomotor is drained to the crankcase of the engine through the reversing control valve. AXIAL SHIFTING OF CAMS (Mitsubishi and MAN Engines) In this case there are two sets of cams (ahead cam & astern cam) one for ahead running and other for astern running. To engage the correct cams for ahead or astern operation with cam rollers, the camshaft slides axially in its bearings. The camshaft reversing gear, which is usually a piston operating in a cylinder, controls this axial movement. Motion of the piston is transmitted directly to the camshaft. Reversing handle Starting Lever

Interlock signal Air to power bottles Lube. Oil. Control air

Reversing relay

Power Bottles

Safety gear with stopper Camshaft Cylinder

Piston

AXIAL SHIFTING OF CAM The camshaft reversing gear consisting of the piston is sometimes referred to as the camshaft servomotor. It may be actuated by hydraulic or pneumatic means. In some cases the hydraulic system is fed from the main engine lubricating oil system, the pressure being sufficient to operate the servomotor piston. Pneumatic servomotor is usually supplied with air from the starting air system. Oil dash pot connected to the cylinder smoothes out the motion of the parts and prevents shock. The incline between the ahead and astern cams allows the cam rollers to Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers transfer from one cam to the other when the adjacent cam is in an open position. Some engine builders put a corresponding chamfer or a good radius on the cam roller edges. In older slow speed engines, the shaft carrying the rocker arms had eccentrics on it, the eccentrics being the fulcrum for the rockers arm. Rotation of the rocker shaft lifted the rocker arm and roller clear of the cam peaks so that axial movement of the camshaft could be completed. When the camshaft was in its new position, continuous rotation of the rocker shaft lowered the rockers and rollers on to the duplicate cams. In modern’s engines, the axial distance of each pair of cams is made sufficiently large so that the side of each pair of cams is made sufficiently large so that the side of the peak of one cam inclines off slowly to the idle part of its adjacent duplicate cam. These inclined planes between pairs of cams enable the rollers to slide from one cam to another, even in the most unfavourable position of the cams. Description of the system adopted for Axial Shifting of Camshaft Switching of running between ahead and astern is made by means of a camshaft shifting mechanism, called “reversing gear”, which shifts the entire member of camshaft back and forth to lead it on the cam position either ahead and astern respectively in the manner that the reversing handle actuates the reversing relay valve which sends the compressed air into the hydraulic oil tank, either on its ahead side or astern side, where by the air pushes the hydraulic oil into the ahead side or astern side of the reversing cylinder and shall stay on the astern position as long as the reversing handle is put on the position ahead. Reversing gear consists of a cylinder, a piston, and safety gear and power oil bottles. In the cylinder, is encased the piston which is shifted back and forth by means of the force of the hydraulic oil filling up in cylinder. The piston is coupled with the camshaft. On the cylinder top, is fitted, a safety gear with a stopper. When reversing Handle when shifted to another position, the reversing relay valve is so actuated as to let the compressed air go through the safety gear to push the stopper and get into the hydraulic tank. The air then actuates the hydraulic oil so that it gets the reversing cylinder to force the piston to move. When a complete course of camshaft shifting is over, then move the reversing handle to the position running where by the hydraulic oil that have been pushing the piston is so released as to get back to the hydraulic oil tank, where by the compressed air is to escape through the reversing relay valve out into the engine room, where by the safety gear stopper is lowered back so as to hold the piston immobile, lest the camshaft would not move any more. The main handle is provided with an interlocking device that holds the main handle immobile so long as the reversing handle should not be on position ‘running’. Another one more interlocking device is fitted to the main handle, by which main handle is not capable a full-course of a shifting either to ahead or astern position right after the reversing handle was so worked, or, in other words, unless the safety gear stopper should come down on the low position where it keeps the position immobile. Shifting Position of Rollers on the Cams (MAN B&W S/L/K MC Engines) Reversing of engines by changing the fuel pump timing is accomplished by shifting the roller position on the cam. In this mechanism position of roller is shifted by corresponding angle required for reversing and roller is locked in this position to be required to operate in desired direction of rotation. This shifting of fuel cam is accomplished by operation of air cylinder connected to this roller mechanism. This system is independently fitted to each cylinder unit. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers This system is simple and safe. Reversing can be operated even if one or two cylinders have not operated to its correct position. Roller Displacement All the controls achieved in these engines are achieved by pneumatic means. There are two cylinders for changing the fuel timing and air starting timing in way of fuel rollers and air distributor respectively. When the ahead/astern order is received by the telegraph the compressed air to the telegraph sent a pneumatic signal to either ahead/astern solenoid to open, upon which the control air goes to the fuel and distributor cylinder to shift to the position of the telegraph order. On achieving the set position the air distributor is locked into position by solenoid valve which are operated by a tapoff from starting air pilot line after the turning gear interlock. The fuel rollers are of self-locking type on change of position of rollers.

CRASH ASTERN This reversing is normally referred to as braking momentum of engine in case of emergencies. This process is normally incorporated in control system of an engine. In this case, engine is stopped from full speed. However propeller revolution does not come down to zero immediately due to momentum of ship, current, wake and wind. However in case in emergency, engine is reversed when the RPM comes down to predetermined safe level, for reversing, when engine RPM is brought to zero by air braking in reverse direction and then engine is cranked in reverse and the engine is started on fuel till momentum of the ship is stopped. EMERGENCY CONTROL Normally referred to engine operation from local control of engines outside control room or bridge. When all remote control operations are by passed and all basic operations of engine are functional. All engineers should familiarise with the operation so that ship can be safely manoeuvred in case of remote control failure where fault cannot be repaired immediately or fault can be easily traced. Which can be done later after the ship has been safely manoeuvred. All remote control safeties like auto slow down function normally connected with cylinder oil non-flow, high crankcase mists, high scavenge temperature and other safeties are normally eliminated in this mode of control. However basic safeties like lube Oil low-pressure trip, over speed stop and cooling water high temperature stop are normally functional even in this control. Depending on the arrangement, governor may be connected or disconnected in local control. For engine fitted with electronic governor, governor is bypassed in local control. Emergency Operation An engine, which is pneumatically controlled (pneumatic remote control) can be in operation if following were to take place.  Remote control pneumatic systems were to fail.  Pneumatic speed controls were to fail.  Governors were to fail. So to keep the engine in operation in these conditions to occur individually or collectively some arrangement are provided on the engine. It is, however, necessary that the input for operation of shut down servomotor and solenoid valve for the safety shutdown of the fuel injection pumps be interrupted. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers Remote Control Pneumatic System Failure The selector switch is brought to engine side control and the control of engine operation brought to local control status, were by operation of the engine is possible by starting air fuel operation apart from ahead/astern selector switch/lever to take place mechanically. Pneumatic Speed Control Failure The telegraph position is related to the ship speed, which in turn is governed by engine RPM. The failure of this system would render the engine inoperative. Hence a mechanical fuel control is provided on the engine. Governor Failure The governor is to be isolated from the pneumatic control system and is to be connected to mechanical linkages for fuel regulation. INTERLOCKS AND BLOCKING DEVICES Engines are fitted with safety devices, which are regulatory body requirements to prevent damage to the engine and eliminate any hazards to life and environment. Interlocks and blocking devices are provided so that the engine can be started or reversed only after certain conditions have been fulfilled. The starting interlocks prevent the engine being put onto fuel before all the sequences of engine system have been completed. During the reversing of engines the interlock ensures that the reversing mechanism and gear have completed all operations before all can be put on to the starting valves, thus preventing the engine from starting with the wrong direction of rotation. The construction of the interlocks in the starting and reversing gear varies considerably between different designs of engines, with system controlled by the operation of hand levers, the interlocks may be cam(s) or pin(s) which lock and prevent hand levers movement. In engines controlled by hand-wheel controls, the interlocks are often slotted disc (fitted on the wheel shaft) and small levers, which engages or clear the slots in the discs. Blocking devices are mechanical, pneumatic, electrical or hydraulic devices used to make for safer operation of the engine. Some engines have a blocking devices connected with the ships engine room telegraph which prevents the engine being put astern when an ahead order is given, and vice versa. Blocking devices is fitted to the engine turning gear so that the engine cannot be inadvertently started with the turning gear is in. In the event of engine room telegraph failure, any interlocking and blocking devices operated from the telegraph would prevent the engine being manoeuvred during this time of emergency. It is therefore important to know how the interlock and blocking devices may be overridden so that the engine can be manoeuvred under emergency condition with orders via the bridge to engine telephone or sound signals (code). Safety Features of these Interlocks are  Air should not be admitted into the cylinder during reversing operation or when servomotor is in operation.  Fuel admission to cylinder, only after the engine starts rotating in the same direction as set by the telegraph.  Fuel supply should be cut off when the lube oil, cooling water pressure etc. decreases below the minimum limit. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers Turning Gear Interlock It is a device, which prevents the engine from starting if the turning gear is engaged. Camshaft Interlock It is a device, which prevents the engine from starting if the camshaft has not shifted or changed its end position in compliance with engine order telegraph. Running Direction Interlock/Reverse Safety Device This device prevents fuel injection to the engine if the engine rotates in the wrong direction. Operation of the engine on fuel under this condition usually causes the cylinder relief valves to lift. Starting Air Distributor In End Position Interlock This device prevents starting from taking place if the shifting of the distributor has not been completed. Fuel Pumps Interlock It prevents reversing of engine if the fuel rack is not in its zero injection position. Automatic Water and Lube Oil Pressure Safety Cut Out Should the water (cooling) or lube oil pressure goes beyond the minimum set pressure for safe operation of the engine it actuates the fuel pump, cut off fuel to the engine. Auxiliary Blower Interlock It is provided in case of constant pressure turbo charging. This ensures sufficient air during low speed running, which is essential for proper combustion. Air Spring Interlock The air spring (for exhaust valve) pressure must always be maintained; else the exhaust valve may not close while running. TIMING ARRANGEMENT FOR DISTRIBUTOR The distributor camshaft drive in synchronised with the fuel camshaft. When the engine is reversed the position of the air distributor cam is also turned to admit starting control air to starting air valves according to the reverse firing order. The distributor is arranged radially in the same plane as with the cam so that a single cam can operate them. There are other arrangements in which different cams are used for ahead and astern running. In such a system the camshaft is moved axially for reverse setting of fuel and distributor cams. Since the admission of air follows the same crank sequence as the fuel cam, the two motions can be synchronised.

Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers REGULATORY BODY REQUIREMENTS FOR A REVERSIBLE ENGINE  In order to maintain sufficient manoeuvrability of a ship in all normal conditions, the main propulsion machinery is to be capable of running the ship astern.  The main propulsion machinery is to be capable of maintaining in free route astern at least 70% of the ahead revolutions for a period of at least 30 minutes.  The Ahead revolutions as mentioned above are understood as those corresponding to the maximum continuous ahead power for which the vessel is closed.  The reversing characteristics of the propulsion plant are to be demonstrated and recorded during trails.  The power developed in astern direction should be 60% of ahead.  Air bottle capacity should be such that 12 consecutive starts is achieved in alternate direction i.e. ahead-astern-ahead…  Air compressor capacity is such as to fill up the air bottles from atmospheric pressure to the total capacity within one hour. SOLAS Requirements: Chapter Two (Reg. 28 & 03)  Sufficient power for going astern shall be provided to enable proper control of the ship in all circumstances.  Machinery should be able to reverse the direction of thrust of the propeller to bring the ship to rest from maximum ahead service speed in sufficient time and reasonable distance. This shall be shown and recorded.  Maximum astern speed: it is the maximum estimated speed reached by the ship at the designed maximum astern power at the deepest sea going draft. AUTOMATION IN REVERSING  Now a day the engine room-manoeuvring device is mostly placed in a console at some distance from the engine. If the movement of this device is transmitted mechanically to the engine, there will always be a play involved, which depends on the distance and on the number of joints in the linkage.  The pneumatic remote-control system is free from this disadvantage, and it is therefore very suitable for automation of the engine from remote (engine control room and bridge).  For this pneumatic system, impulse air is taken from the starting air receivers through air filters, oil-mist lubricating devices and pressure regulations, reducing the air pressure to 8 bars.  The component of the system are of standard type and widely available. They require a minimum amount of maintenance and are easy to overhaul. The function of the control system 1. Starting, stopping and reversing of the engine. 2. Regulating the engine speed and load. 3. Protecting and monitoring the engine.  All functions of the control system are controllable. The interlock in the control system guards against false manoeuvring.  Safety devices protect the engine from damage in both normal and emergency operation.  Functions of remote control. 1. Bridge: Ahead/astern changeover Starting Speed setting/governor control, including program control Stopping Normal reversing Engineer M. A. Hamid 9

REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers -

Harbour reversing Crash reversing Quick passage device of critical speed range. Barring of critical running RPM because of torsion vibration Racing control

Control room Ahead/astern changeover Starting Speed setting/governor control, including program control Stopping Normal reversing Harbour reversing Crash reversing Quick passage device of critical speed range. Barring of critical running RPM because of torsion vibration Racing control Upper speed limit Air running 3. Back up control/engine side controlAhead/astern changeover Starting. Speed setting/governor control. Stopping. Scavenging air torque limit cancel. SOLAS Requirements:  Means of preventing overload of propulsion machinery.  System shall be provided with an emergency-stopping device on the bridge. It shall be independent of the navigation bridge control system.  Order from the bridge shall be also indicated in the engine control room.  Remote operation of propulsion system shall be possible only from one location at a time. Each location shall have indicators showing which location is in control. (While transferring control, there shall not be significant change in propeller thrust; means to confirm this is to be provided.)  Control of the propulsion machinery from local position in the event of failure of automation or remote control system, should be possible.  In case of remote automatic control system failure, an alarm should be given off. Control now should be possible from the control station. Movement of the control (telegraph) from stop must first initiate checks like a) Turning gear is disengaged. b) Starting air is available at correct pressure. c) Cooling water, lube. Oil and fuel oil supplies are in order before the starting sequence begins. Starting sequence will include the following: a) Camshaft is correctly positioned. b) Starting air is admitted, shaft turns in right direction to that of order. c) Shaft has gained sufficient speed to cause sufficient compression pressure for combustion. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers d) Fuel is admitted. e) Starting air is shut off. f) Speed is adjusted as per the control position. If the initial firing revolutions at starting are not reached within a fixed period, usually about 3 sec a further period of about 4-sec is allowed to elapse and the cycle is repeated, still under automatic control. Normally after three false starts the operation ceases and an alarm functions. Interlock-1: It confirms that the camshaft has shifted to desired position. If yes the subsequent signal is given for starting air sequence to start. Interlock-2: It conforms that the engine has achieved RPM that is sufficient to cause combustion and is also in correct direction. If yes the subsequent signal is given for acceleration programme to start the fuel injection. BRIDGE CONTROL OF DIRECT DRIVE DIESEL ENGINE Two consoles would be provided one on the bridge the other in the engine control room. For the bridge console the minimum possible alarms and instruments would be provided commensurate with safety and information requirements e.g. low starting air pressure and temperature, sufficient fuel oil, fuel oil pressure and temperature, etc. the engine room console would give comprehensive coverage and overriding control over that of the bridge. The selector would be in the engine room console and the operator can select either engine room or bridge control, with one selected the other is inoperative. Assuming bridge control a programme would be selected, say half astern, then providing all safety blockages such as no action with turning gear in etc. are satisfied, the programme can be initiated a sequence of checks as mentioned in program control. Essential safety locks, such as low lube. Oil pressure or cooling water pressure override the programme and will stop the engine at the same time as they give warning. Direct local control at the engine itself can be used if required on in the event of an emergency. Further more protective considerations are: Governor, including over speed trip. Non-operation of air lever during direction alteration. Failure to fire requires alarms indications and sequence repeat with a maximum of say 4 consecutive attempts before overall lock. Movement of control lever for fuel for a speed out of a critical speed range if the bridge speed selection within this range. Emergency full ahead to full astern timing and settings MAINTENANCE AND TROUBLESHOOTING Preventive maintenance is preferred according to a schedule as recommended by the manufacturer and as amended by the operator in light of continuing experience. Starting valves: - Lubricate during manoeuvres. - Retighten valve spindle after 200-300 starting air manoeuvres, Grind if necessary. - Automatic starting air stop valve and non-return valve- Drain after each manoeuvring period. Camshaft drive: Check gear/camshaft chain wheels and lube nozzles. Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers -

Regulating linkageGrease.

Fuel injection valve: Clean, check and readjust injection pressure. Check holes for wear. Pneumatic solenoid valve: Periodic maintenance as per recommendations from manufacture. Typical job involves cleaning of the valves off oil/dirt and renewal of gaskets. Engine cannot be Reversed or can be Started only in one Running Direction: 1) There is only an insufficient control pressure or none at all. 2) If the engine cannot be reversed when stopping the vessel, this may also be due to an inadequate torque on account of insufficient air starting air pressure or a defective starting air control slide valve or starting valve. 3) The reversing gear is stuck at end position or shortly before end position, thus not releasing control signal to the blocking device of the starting lever. 4) The running direction safety interlock, or its control slide valve, is stuck in an end position. 5) Control oil pipes or ducts are obstructed or heavily leaking, so the pressure is too low. 6) The reversing valve becomes loose and has been turned relative to the lever. Engine starts in the Wrong Running Direction when being reversed: 1) The engine room telegraph has been fitted facing in the wrong direction. 2) The reversing valve, or the rotating slide valve, of the running direction safety interlock has been incorrectly fitted. 3) The running direction safety interlock is out of action if the cut out servomotor is stuck. 4) In control oil pipes of the reversing gear are in correctly connected. ELECTRONIC OPERATION The signal received by the electro hydraulic servo valve and the control valve is from cylinder control unit installed for each cylinder. The engine control system is connected to ships control system. This ship’s control system has two control units. 1) Cylinder control unit for each cylinder. 2) A local control terminal. Engine Control Unit’s Function: It relates to overall situation of the engine and connects plant control system, safety system and supervision and alarm system with inputs from sensors and actuators. Cylinder Control Unit’s Function: It connects all functional components to be controlled at each cylinder, e.g. fuel injection, exhaust valve, starting valve and cylinder lubrication. As faults can never be completely ruled out each cylinder has a cylinder controller, who’s failure will result in temporary loss of power of concerned unit until the standby engine controller takes over and continues the operation without any change in performance. Electronic Control of Fuel Timing Operation of fuel valve is governed by a microprocessor (computer). For correct operation inputs of engine speed and crank angle is given to the microprocessor, which controls the Engineer M. A. Hamid

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REVERSING OF TWO-STROKE ENGINE Note Book For Marine Engineers operation of fuel valve. Here the metering of fuel volume for one cylinder is not governed by delivery volume per stroke but by limiting the duration of injection. This is made possible by an electronic controller i.e. a low voltage signal that controls the opening and closing action of electro-hydraulic servo valve. This opening and closing of electro-hydraulic servo valve connects and isolates the fuel valve from the servo oil accumulator, which finally operates the fuel valve. Each cylinder unit is provided with a servo oil accumulator to ensure sufficient fast delivery of servo oil per injection requirement. A number of injections patterns are stored in the microprocessor, which are selected by the control system so as to operate the engine with optimum injection characteristics from dead slow to overload, as well as during astern running and crash stop. Electronic Control of Exhaust Valve Timing The exhaust valve is driven by the same servo oil system as that for the fuel injection system, using pressurised cool, clean lube oil as the working medium. The operation of exhaust valve only controls the time of opening and closing the valve. This is obtained by using a simple fast acting ON/OFF control valve to control the movement of the exhaust valves. The control valve being again operated by the microprocessor, which operated the fuel valve. PROGRAM CONTROL All operations should take place automatically without intervention by the officer in control, and he should receive a signal confirming that the orders have been obeyed. For example, following sequence for start in half astern: - Ensure fuel at zero. - Admit starting air in correct direction. - Check direction. - Time delay to allow engine to reach firing speed. - Admit fuel. - Time delay to cut off air. - Time delay and check revolutions - Adjust revolution. - Lever travel time to full can be varied from stop to full between adjustable time limits of half minute to six minutes. References:  Marine engineers review (India).  IRS-part 4 chapter 2(1.10) [main and auxiliary machinery]  SOLAS-Chapter 2 Regulations 3 & 28.  Automation and control systems for marine engineers by Vikram Gokhale and N. Nanda.  Basic marine engineering by J.K.Dhar.  Motor engineering knowledge for marine engineers volume 12, REED series.  Question and answers by Lamb.  Marine diesel engines by Pounders.  Sulzer diesel engine manuals.  MAN B&W diesel engines manuals .

Engineer M. A. Hamid

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