Q:- With specific reference to any make, sketch and describe the Cylinder Lubrication system used in new generation marine diesel engines.
How will you effect the optimum cylinder oil feed with varying sulphur content of fuel oil.
SYSTEM EXPLANATION
This cylinder lubrication, shown in the figure is based on a lubricator which injects a specific volume of oil into each cylinder for each (or for every second, third, etc.) revolution. The oil fed to the injectors is pressurised by means of Alpha lubricator on each cylinder, equipped with small multi piston pumps. The amount of oil fed to the injectors can be finely tuned with an adjusting screw, which limits the length of the piston stroke.
The dosage of oil can be adjusted means of an adjustment screw which limits the stroke of the main lubricator piston. After a predetermined time interval, the computer transmits an OFF signal to the solenoid valve, which shuts off the system pressure and opens the return oil system.
The amount of oil injected varies as required, e.g. at load changes, start/stop, or increased engine load. Alternatively, the dosage of oil fed to the individual cylinders can be adjusted by injecting a calibrated amount of oil, a number of times, at a given number of revolutions. A combination of the two systems can also be used.
A pump station delivers lube oil to the lubricators at 45 bar pressure. The lubricators have a small piston for each lube oil quill in the cylinder liner, and the power for injecting the oil comes from the 45 bar system pressure, acting on a larger common driving piston. Thus, the driving side is a conventional common rail system, whereas the injection side is a high-pressure positive displacement system, thus giving equal amounts of lube oil to each quill and the best possible safety margin against clogging of single lube oil quills.
For the larger bore engines, each cylinder has two lubricators (each serving half of the lube oil quills) and an accumulator, while the small bore engines (with fewer lube oil quills per cylinder) are served by one lubricator per cylinder. The pump station includes two pumps (one operating, the other on stand-by with automatic start up), a filter and coolers.
The lubricator can be delivered for our conventional engines in which case it is controlled by a separate computer unit comprising a main computer, controlling the normal operation, a switchover unit and a (simple) back-up unit. A shaft encoder supplies the necessary timing signal in that case. When used on ‘Intelligent Engines’, these functions are integrated in the engine control computers and their shaft encoders.
The lubrication concept is intermittent lubrication – a relatively large amount of lube oil is injected for every four (or five or six, etc.) revolutions, the actual sequence being determined by the desired dosage in g/bhph. The injection timing is controlled precisely and – by virtue of the high delivery pressure – the lube oil is injected exactly when the piston ring pack is passing the lube oil quills, thus ensuring the best possible utilisation of the costly lube oil.
The safety features of this system are as follows:
In the event of malfunctioning solenoid valve or transducer, the oil dosage will automatically be increased to the maximum volume. If the oil pressure falls, the computer will start stand-by pump, close down the faulty pump and sets on the alarm.
In this system if one lubricator malfunctions (980-700 mm bore engines), the oil dosage from the other lubricator will be automatically doubled, and an alarm will be given whereas for 600-260 mm bore engines, alarm and slow down ensue.
An inductive sensor in each lubricator monitors the movement of the lubricator piston a signal is sent to the control computer system which has a backup for safety.
Alpha ACC (Adaptive Cylinder oil Control)
The principle of the Alpha ACC
The basic feed rate control should be adjusted in relation to the actual fuel quality and amount being burnt at any given time. The sulphur percentage is a good indicator in relation to wear, and an oil dosage proportional to the sulphur level will give the best overall cylinder condition.
The following two criteria determine the control:
The cylinder oil dosage shall be proportional to the sulphur percentage in the fuel
The cylinder oil dosage shall be proportional to the engine load (i.e. the amount of fuel entering the cylinders).
The implementation of the above two criteria will lead to an optimal cylinder oil dosage, proportional to the amount of sulphur entering the cylinders.
With the introduction of the electronically controlled Alpha Lubricator system, featuring the easy-to-operate “HMI” panel, such adaptive lubrication has become feasible.
The Alpha Lubricator system offers the possibility of saving a considerable amount of cylinder oil per year and, at the same time, to obtain a safer and more predictable cylinder condition.
The basic feed rate control should be adjusted in relation to the actual fuel quality being burnt at a given time.
This new cylinder oil control principle is called the “Alpha Adaptive Cylinder oil Control”, or abbreviated “Alpha ACC”.
the ACC factor can only be assessed when the fuel sulphur level has been high enough to ensure that the lubrication has been in the ACC active area (the blue area marked in Fig. 1), at lower fuel sulphur levels the engine is excessively protected against corrosion because of the active minimum feed rate.
This is important in order to prevent over-lubrication at low loads, and it is one of the main parameters to save oil, compared with conventional lubrication.
When starting to burn new bunker oil, the HMI setting of the Alpha ACC should be adjusted according to the bunker analysis results.
