Air Starting Systems

INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE .

AIR STARTING SYSTEM OF A MARINE DIESEL ENGINE – SULZER.

The Air Bo ttle is linke d to the Air start in g manif old th ro ug h the Automatic air starting valve, which has a non-return valve to prevent the possibility of a blow-back, from a starting air line explosion, to the Air bottles. The Automatic air starting valve is operated by means of the pilot valve shown, which in turn is operated by the starting lever through the starting valve. The turning gear interlock prevents the engine from being started, with the turning gear engaged. The starting air, from the starting valve, also acts to engage the Distributor. This is a safety feature, which prevents the engine from accidentally being started, in the event of air leakage from the Automatic air starting valve. The cylinder air starting valves are operated by the Distributor, in the correct sequence for starting (the Firing order). Reversing : In case of reversal, two things need to be done – firstly the fuel cams need to be repositioned correctly for the astern direction, and secondly

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE the Distributor cam needs to be repositioned, to give the correct sequence for starting in the astern direction. In the engine shown, the camshaft is repositioned by a reversing Servo-motor, to do both these things, since the fuel cams are mounted on the camshaft, and the Distributor also gets its drive from the same source, i.e. the camshaft. Running Direction interlock : If the direction of rotation of the engine is contrary to the command from the Telegraph, we consider it as the 'wrong' direction. In this situation, the fuel cut out servo must operate to shut-off fuel, in case the engine is already runnin g . In addition, the starting air is not allowed to be released, thus preventing the re-starting of the engine in the wrong direction. The Running direction interlock in this en g ine is connected to the camshaft, and will be operated by the movement of the camshaft. If the camshaft does not reverse, then oil pressure does not act on the fuel cut-off servomotor, as can be seen in the sketch below. Thus fuel is cut-off.

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE

CONTROL Direct reversing engines In order to manoeuvre a ship, the propeller thrust must be reversible, by means of reversing the propeller drive or by altering propellers, or diesel-electric drive, allow the use of unidirectional (non-reversible) engines. In systems of limited power using medium or high speed engines through gearboxes, arrangements of clutches and reverse gears may be used. In many ships, however, it is necessary for the main engines to be reversible and able to operate efficiently in both ahead or astern. To run in the astern direction, all the operations in the engine cycle may need retiming. The starting air must first rotate the engine in the reverse direction and this will require retiming the distributor to supply compressed air to the appropriate cylinders in the correct order. The retiming may be carried out by altering the position of the distributor cam drive with respect to its drive from the main camshaft. The number of other readjustments to be made and the methods used depend upon the engine cycle and type. For –stroke engines will require a change in timing of the fuel pumps, a different change for the air inlet valves, and yet another for the exhaust valves. To obtain all these changes on the same camshaft a separate set of astern cams are fitted. Each one is fitted to the camshaft adjacent to its corresponding ahead cam. The reversing procedure is then carried out by moving the whole camshaft axially, which moves the ahead cams clear of their followers which now engage the astern cams. Ramps (sloping sides) fitted between corresponding ahead and astern cams cause the follower roller to slide gently from one to the other. The axial movement is carried out by a hydraulic cylinder fitted to the camshaft; locking devices and safety cutouts ensure that the camshaft ahs carried out its full movement and is in the correct position before the engine can be restarted. To maintain alignment of the camshaft drive, a spline coupling may be necessary. Turbochargers are of course unaffected by reversal of the engine, but engine driven pumps must be reversible. Large two-stroke engines have scavenge ports to control scavenge timing. This must therefore be symmetrical and will this be unchanged when reversing. Engines operating with constant pressure turbocharger systems have almost symmetrical exhaust valve timing, consequently no change in timing is necessary for exhaust cams.

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE Fuel pump timing must be readjusted since it will be the opposite flank of the cam which will now raise the pump plunger to deliver fuel. There are altermative methods employed to change the fuel pump timing without altering the main camshaft and two are illustrated and described. As the camshaft timing has not been altered, any auxiliary drives taken from it are unaffected. This is particularly useful if rotating balancing systems are in use.

Sulzer RTA engines have oil pressure operated hydraulic ‘lost motion’ seryomotors on the camshaft which rotate the fuel pump cams to their astern positions (Fig. 77). Fuel pumps and their cams are grouped in pairs along the camshaft and a servomotor is fitted for each pair of adjacent cams. Oil pressure secure each servomotor in its correct position while the engine is running. ‘Lost motion’ is the term used to indicate that the timing has been retarded, or moved back, through a given angle with respect to the ‘new’ direction of rotation. MAN-B&W MC engines have their fuel pump cams fixed directly to the camshaft but the follower rollers can be displaced to alter the pump timing as shown in Fig. 78. The link which displaces each follower is actuated by a pneumatic piston using compressed air from the starting systems. The link is self-locking in either position and a sensor to shut off the pump in the event of mal-operation.

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE Reversing servomotor, Sulzer RTA engines. A similar servomotor is used to retime the starting air distributor at its drive from the camshaft.

MAN – B & W reversing system. Pnuematic cylinders are fitted to each fuel pump and will cut off the fuel if the reversing lever is in the incorrect position. The link is self-locking in either position.

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE

AIR STARTING VALVE OF A SULZER MARINE DIESEL ENGINE

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE

AIR VESSELS Material used in the construction must be of good quality low carbon steel similar to that used for boilers, e.g. 0.2% Carbon (Max.) 0.35% silicon (max.), 0.1% manganese, 0.05% sulphur (max.),0.05% Phosphorus (max.), u.t.s. 460 MN/m2. Welded construction has superseded the riveted types and welding must be done to class 1 or class 2 depending upon operating pressure. If above 35 bar approximately then class 1 welding regulations apply. Some of the main points relating to class 1 welding are that the welding must be radiographed, annealing must be carried out at a temperature of about 600 0C and a test piece must be provided for bend, impact and tensile tests together with micrographic and examination. Mountings generally provided are shown in Fig If it is possible for the receiver to be isolated from the safety valve then it must have a fusible plug fitted, melting point approximately 1500C, and if carbon dioxide is used for fire fighting it is recommended that the discharge from the fusible plug be led to the deck. Stop valves on the receiver generally permit slow opening to avoid rapid pressure increases in the piping system, and piping for starting air has to be protected against the possible effects of explosion. Drains for the removal of accumulated oil and water are fitted to the compressor, filter, separators, receivers and lower parts of pipe-lines. Before commencing to fill the air vessel after overhaul or examination, ensure : 1. Nothing has been left inside the air vessel, e.g. cotton waste that could foul up drains or other outlets. 2. Check pressure gauge against a master gauge. 3. All doors are correctly centred on their joints.

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INSTITUTE OF ENGINEERING TECHNOLOGY - KATUNAYAKE

Run the compressor with all drains open to clear the lines of any oil or water, and when filling open drains at regular intervals, observe pressure. After filling close the air inlet to the bottle, check for leaks and follow up on the door joints. When emptying the receiver prior to overhaul, etc., ensure that it is isolated form any other interconnected receiver which must, of course, be in a fully charged state. Cleaning the air receiver internally must be done with caution, any cleaner which gives off toxic, inflammable or noxious fumes should be avoided. A brush down and a coating on the internal surfaces of some protective, harmless to personnel, such as a graphite suspension in water could be used.

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