marine engineering

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Marine generators driven from the main propulsion system

Generators can variously be driven from the propeller shaft, through a gearbox or by being mounted on the engine itself. Assuming that residual fuel is used in the main engine, then all electrical power at sea is provided at much lower cost, in terms of fuel price and auxiliary generator running hours. The diesel driven generator is needed only while manoeuvring and in port.

Shaft driven direct current generators

Direct current generators are not as sensitive to speed variation as are alternating current machines where frequency has to be maintained. If a direct current generator has an automatic voltage regulator, the output voltage can be maintained even with a 10 or 15 per cent speed reduction. Belt driven or shaft mounted direct current generators with automatic voltage regulators were therefore fitted in ships to save space and to reduce the workload. These machines could continue in operation with moderate speed reduction but auxiliary diesels were brought into use when manoeuvring.

Alternators driven from the main propulsion system

One answer to the frequency problem with alternators, is to supply direct current from a shaft driven direct current generator to a direct current motor and to use this to drive an alternator at constant speed. This arrangement permits moderate main engine speed reduction before a change over to auxiliary generators is necessary.

Another solution to maintaining alternating current frequency, relies on the use of a controllable pitch propeller and constant speed engine, rather than one which has to be directly reversed. Manufacturers of electrical equipment have also developed various types of electronic circuits to maintain level frequency through main engine speed changes,

Mechanical constant speed drive from variable speed engine

The system shown (Figure 7.12) uses speed increasing gears to deliver drives from the main engine system to two parts of the installation. One gear train drives a variable delivery hydraulic pump (shown at the bottom). The other drives the planet carrier for the epicyclic gear train A. Rotation of the planet carrier A with the central sunwheel B fixed, causes the annulus C to drive through its output shaft, the gear train for the generator. Any steady rotation of B will affect the generator speed and frequency.

When the speed of the main propulsion system is altered, this is sensed by an electronic device on the generator and the signal is used to control the swashplate for the variable displacement hydraulic pump unit. The output from the latter drives the fixed-displacement hydraulic unit which is connected to the sunwheel E. The annulus for this epicyclic gear is fixed so that rotation of the sunwheel E, drives the planet carrier G and through the shaft, sunwheel B. The

Figure 7.12 Constant speed shaft generator drive (Vickers type)
Figure 7.12: Constant speed shaft generator drive (Vickers type)

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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