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Starting & Reversing

Starting & Reversing System Prepared by P. Mukherjee. Starting & Reversing. Overview All direct drive large diesel engines used for ship’s propulsion has a starting & reversing system.

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Starting & Reversing

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  1. Starting & Reversing System Prepared byP. Mukherjee

  2. Starting & Reversing Overview • All direct drive large diesel engines used for ship’s propulsion has a starting & reversing system. • It includes starting, stopping, reversing and speed regulating of the engine. In most modern engines, all those operations are performed by • Automatic operation from bridge • Automatic or semi-automatic operation from ECR • Emergency manual operation on engine

  3. Starting & Reversing Learning Objectives • Explain the principles of air starting system of large marine diesel engines • Describe the operation of main components of air starting system • Explain the principles of reversing of modern 2-stroke and 4-stroke engines • Explain various methods of reversing for 2 & 4 stroke engines • List and explain the operation of safety interlocks normally fitted in the manoeuvring system

  4. Basic Concept of Starting D.E. High initial torque is necessary to accelerate the engine, so that sufficient compression pressure is produced to create high temp in the cylinder for fuel to ignite ( 540OC) . Torque has to overcome : • Forces of adhesion of bearing surfaces due to presence of cold oil • Load coupled to the engine • Compression force • Effect of cold combustion chamber walls, which lowers the temp of compression

  5. D.E. Starting Methods • Manual Starting • Electric Starting • Hydraulic Starting • Air starting

  6. Principles of Air Starting System • Medium & high powered engines are started with compressed air to a sufficient speed for operation on fuel • To achieve this, engines are fitted with Starting air valves controlled by a Distributor • Distributor is to ensure: • air is introduced into relevant cylinder in correct time • starting of engine in a desired direction • staring of engine from any position of rest • Starting sequence is same as the firing order of the engine • Air is usually introduced slightly after TDC during the power stroke • Air admission is stopped before opening of exhaust valve • Overlapping is provided to ensure positive starting in correct direction

  7. Air Starting System Design Consideration For engine to start on air with sufficient turning moment, A > B A = starting air pressure x area of piston x stroke B = mean compression pressure x area of piston x stroke The factor A has to be significantly greater than B, depending upon: • Friction & mechanical resistance to overcome • Momentum of moving parts by the time compression starts • Initial inertia force to overcome It is essential that at all angular position there is sufficient starting air turning moment available to ensure a positive start. For that reason minimum overlap of 15O is provided.

  8. Starting & Reversing How “Starting air pressure < Pcom” can turn Engine ? Because ---- • Starting air pressure is greater than mean compr. pressure • Momentum of flywheel & other moving parts assist in overcoming the compression pressure

  9. Starting & Reversing Diagram shows air starting Pressure, below compression Pressure, can turn the engine

  10. Starting & Reversing

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