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Marine auxiliary engine hydraulic governor
Governor or speed governor – During normal operation, the engine speed is controlled by
a governor which regulates the injected fuel quantity corresponding to the load. The
governor shall prevent the engine from exceeding the rated speed by more than 15%.
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. The governor has adjustable speed drop and load limit controls. A split field, electric motor-operated speeder gear to facilitate remote alteration of engine speed setting from the switchboard is incorporated. This alters the spring pressure usually through a screwed rod.
Figure 7.10 Dial control governor without auxiliary equipment
The Woodward hydraulic governor (Figure 7.10) is briefly described as an example of a commonly fitted type. This has a gear pump driven from the engine camshaft to supply the hydraulic oil first to accumulator pistons, under which is a bypass, to regulate maximum pressure. One branch supplies oil which acts on top of the power piston. The pressure from this supply tends to turn the terminal shaft to shut off fuel. The other branch supplies oil to the pilot valve which is operated by the linkage from the flyweights above.
Figure 7,11 Simplified diagrammatic sketch of Woodward governor
Should the speed of the engine decrease due to increased load the flyweights (Figure 7.11) will move towards their centre of rotation and lower the position
of the pilot valve plunger, so that oil is admitted via the pilot to the underside of the power piston. The pressure is now equal on the top and bottom of the power piston. Because the area on the bottom is much greater than the top the net resultant force causes the piston to move upwards, so increasing fuel to the engine as the power lever turns the terminal shaft and fuel rack to give later fuel cut-off. As the power piston moves up, the actuating compensating piston moves down. Oil under this piston is now forced through to the receiving compensating piston, raising the outer end of the floating lever and closing the pilot valve. This stops excessive movement of the power piston and fuel rack.
As the engine speeds up and the flyweights move out towards their former position, the oil holding the receiving compensating piston leaks through the needle valve. The two movements act on the floating lever without moving the closed pilot valve.
A decrease in the load causes the engine speed to rise so that the flyweights of the speed sensing assembly move outwards, raising the pilot valve through the floating lever. This allows oil to escape from beneath the power piston, so that the engine fuel setting is reduced. As the power piston moves down, the actuating compensating piston moves up causing the receiving compensating piston to move down, taking with it the outer end of the floating lever and
closing the pilot valve. This action again stops excessive movement of the power piston and fuel rack. As the engine speed drops, the flyweights move back in towards their former position, while oil leaks through the needle valve allowing the receiving compensating piston to return towards its old position. Again, the two movements act on the floating lever without moving the closed pilot valve.
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Summarized below some of the basic procedure of marine auxiliary machinery :
- Auxiliary engine general construction
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.
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- Auxiliary engine back pressure turbine
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......
- Auxiliary engine 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.
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- Auxiliary engine common fuel injector
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.
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- Auxiliary engine cooling system
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.
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- Auxiliary engine hydraulic governor
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.
......
- Auxiliary engine speed governing system
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.
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- Auxiliary engine 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
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- Generators driven from the main propulsion
Generators can variously be driven from the propeller shaft, through a gearbox or by being mounted on the engine itself.
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- Exhaust gas boilers
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,
......
- Auxiliary engine Turbo generator construction
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.
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- Caterpillar engine fuel system
The range of larger Caterpillar engines use helix-type fuel pumps driven from a
separate camshaft.......
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