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Marine auxiliary engine fuel pump - Bosch type

Bosch type fuel pump : 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.

These pumps can be arranged singly along the camshaft, with one at each cylinder position or they may be housed in a single block. Each pump unit contains a pump plunger and guide together with a spring loaded delivery valve and its seat. Plungers and guides are not interchangeable they should be treated as combined units or elements.

Operation : The operation of helix type pumps is shown diagrammatically in Figure 7.6. With the plunger E at the lower limit of its travel (Figure 7.6a) fuel enters the barrel from the surrounding suction chamber, through the two ports. As the plunger rises, some fuel is displaced through the ports until they are just closed (Figure 7.6b) by the top edge of the plunger. Fuel trapped above the plunger is now forced out through the delivery valve above the top of the pump barrel.

Figure fuel pump assembly
Figure : Sectional views of fuel pump assembly

Sectional views of fuel pump assembly
Figure 7.6:a,b,c Sectional views of fuel pump assembly

The pressure exerted by the rising plunger causes fuel to lift the valve and to enter the pipe which connects the pump to the injector. As the pipe is already full, the extra fuel which is being forced in, causes a rise in the pressure throughout the line and lifts the needle valve of the injector. This causes fuel to be forced into the combustion chamber in the form of a fine spray.

Bosch type fuel pump
Figure 7.7 Bosch type fuel pump

As the plunger continues to move upwards, the lower edge of the control helix uncovers the spill port, allowing fuel to be bypassed from the barrel suction chamber through the vertical drilled hole in the plunger or via a machined slot or channel (Figure 7.7). This allows the delivery valve to shut under the action of its spring, and with the collapse of pressure in the pipeline, the injector also shuts. At the junction between the delivery valve and its guide, there is a short plane cylindrical piston which fills the seat aperture as the valve closes. This emphasizes pressure drop in the delivery pipe so that the injector closes sharply.

The actual plunger stroke is constant, but an effective stroke depends on which part of the helix is moving up and down in line with the spill port. The effective stroke can be set between maximum fuel and no fuel. The latter setting, means that fuel spills for the full length of the plunger stroke. The plunger is moved around to the required position by the rack and quadrant (Figure 7.7).

The quadrant collar is on a sleeve which has two vertical slots at the bottom. Two lugs projecting from the lower part of the plunger move up and down in these slots as the plunger reciprocates. Rotary movement of the sleeve (which has no vertical motion) moves the plunger. The rack which meshes with the toothed quadrant is externally connected to suitable linkage from the governor and the manual control lever.

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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