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Marine auxiliary diesel engine -general requirement & troubleshooting guideline

Diesel driven generators can be expensive in terms of fuel cost and maintenance requirements. Continuous operation at sea and in port exacts a high price particularly if distillate fuel is used. This has led to the use of residual fuel and the introduction of fuel blenders so that heavy residual fuel can be added to the distillate as the load increases to give cost savings. Blenders improve fuel economy but running hours still mount up and routine maintenance is likely to be increased by the use of poor quality residual fuels.

A better economy in the provision of electrical power is achieved with the use of a generator which can be operated at sea, on power derived from the main propulsion system. The ship's electrical load can be provided by a turbo-alternator using steam from a waste heat boiler. The waste heat available from the exhaust of a very large slow-speed diesel engine is sufficient in many installations for the full electrical load at sea.

Savings in fuel costs for such a system amount to about 10% with additional savings in maintenance. However, the continuing search for improvement in diesel engine and propeller efficiency has resulted in the development of very long stroke, very slow-speed engines with constant pressure turbo-charging and the waste heat available from the exhaust has gradually diminished.

The quest for electrical power from the ever decreasing quantity of exhaust gas energy, has fostered progress in the area of harnessing otherwise wasted heat energy. Mechanical generator drives from the main engine, gearbox or the propeller shaft temporarily lost popularity when alternating current power replaced direct current, because frequency demanded a constant speed.

Constant speed drive schemes are now available for use with variable speed engines (and a number of electrical solutions to the problem ). Power turbines, driven by the exhaust gases from the engine in the same way as the turbo-charger, are used to convert waste heat into mechanical energy which is delivered to the main propulsion system through a fluid coupling, or used to provide an integrated drive with a diesel for a generator.

Tracing faults : The failure of an engine to start or problems while running may be traced to faults with the fuel injection system or other possible causes. Instruction manual guidance on fault finding and remedies will include some of the typical problems listed below.

Difficult starting
Poor compression due to any of the following causes:

Summarized below some of the basic procedure of marine auxiliary machinery :
  1. Auxiliary engine general construction

  2. Major problems have been experienced on large slow-speed engines with some of the poor quality bunkers such as those containing catalytic fines. Fuel should conform to the specification given in the instruction book for the engine. ......

  3. Auxiliary engine back pressure turbine

  4. Many ships have used an auxiliary steam turbine as a primary pressure reducing stage before passing the steam to other auxiliaries demanding steam at a substantially lower pressure than that available. Such an arrangement gives a heat balance which is far more favourable than that obtained with a pressure reducing valve......

  5. Auxiliary engine fuel pump

  6. The most common fuel pump used on auxiliary diesel engines is the Bosch type. This is a cam operated jerk pump with a helical groove on the plunger to control the fuel cut-off and therefore the quantity of fuel delivered to the cylinder for combustion. ......

  7. Auxiliary engine common fuel injector

  8. Fuel is delivered to an annular space in the nozzle via a hole, drilled through the nozzle body from the inlet. The nozzle valve is forced from its seat in the nozzle body by the pressure of fuel from the pump, acting on the shoulder of the needle valve. ......

  9. Auxiliary engine cooling system

  10. A variety of cooling systems may be adopted for marine auxiliary engines but the most commonly used is the simple closed circuit system . Sea water is passed through the intercooler, the oil cooler and then the jacket water cooler in series flow. ......

  11. Auxiliary engine hydraulic governor

  12. When used for alternating current power generation, a diesel engine is normally fitted with a hydraulic governor. This incorporates a centrifugal speed sensing device (spring loaded flyweights) controlling a suitably damped oil operated servo-cylinder through a pilot valve. ......

  13. Auxiliary engine speed governing system

  14. Unlike propulsion turbines, generator turbines work at constant speed and must be governed accordingly. Classification Society rules require that there must be only a 10% momentary and a 6% permanent variation in speed when full load is suddenly taken off or put on. ......

  15. Auxiliary engine tracing faults

  16. The failure of an engine to start or problems while running may be traced to faults with the fuel injection system or other possible causes. Instruction manual guidance on fault finding and remedies will include some of the typical problems ......

  17. Generators driven from the main propulsion

  18. Generators can variously be driven from the propeller shaft, through a gearbox or by being mounted on the engine itself. ......

  19. Exhaust gas boilers

  20. The original exhaust gas boilers or economizers were of simple construction and produced, from the low powered engines of the time, a very moderate amount of steam. As large slow speed engine powers increased, the larger quantity of steam that could be generated from otherwise wasted exhaust energy, ......

  21. Auxiliary engine Turbo generator construction

  22. Turbo-generator construction-For electrical power generation, turbines are conventionally horizontal axial flow machines of the impulse reaction type. They may exhaust either to an integral condenser (invariably underslung) or to a separate central auxiliary condenser or the ship's main condenser. ......

  23. Caterpillar engine fuel system

  24. The range of larger Caterpillar engines use helix-type fuel pumps driven from a separate camshaft.......

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