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Ship Auxiliary engine common fuel injector

The fuel injector nozzle contains a non-return valve labelled nozzle valve in the drawing (Figure 1), which is forced open against the spring loading by pressure of fuel from the fuel pump. The upper part of the nozzle (or needle) valve is lapped into the nozzle body within which it works freely. The lower part is of smaller diameter having at its extremity a valve face and at the junction of the two diameters a shoulder. The upper end has a small extension or spigot which engages with the valve spindle.

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. Pressure from the fuel pump also forces the fuel through the holes in the nozzle to form a fine spray in the engine combustion chamber.

Fuel injector assembly
Figure 1 : Fuel injector assembly

When fuel pump delivery ceases, there should be a sharp drop in pressure which means that the nozzle valve will close smartly with an instant interruption of flow.

Injector nozzles normally require cooling when residual fuel is used. Interruption of the fuel valve cooling supply, quickly results in vapour lock of the cooling passages within the nozzles and then blockage by scale. When fuel valve cooling is restored after a failure, it is essential to check flow from all returns, and to clear any with no return flow immediately. Loss of cooling will result in the formation of carbon deposits (trumpets) around the nozzles in a very short time.

Injectors should be taken out for examination, external cleaning and testing at regular intervals based on running hours as recommended by the makers handbook or as dictated by operational factors. Injector opening pressure, spray pattern and effective closing without leakage, are checked with a test pump. Defective injectors require overhaul in very clean conditions with special tools.

On board overhaul may be carried out or alternatively nozzles may be sent to a specialist firm. After a replacement nozzle has been fitted in the nozzle holder, injector spring compression is set on the test rig and then the spray pattern and effective closing are checked.

Inexperienced personnel must be warned against contact with the nozzle tip when testing. Spray intensity is sufficient to puncture the skin and inject fuel.

For cleaning the fuel injectors, a special set of tools is available and contains the following main items: brass wire brush, nozzle body groove scraper, probing tool nozzle body seat cleaner, nozzle body dome cavity cleaner.

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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