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Adjustment of the cylinder lubricant consumption to the most economic feed rate
Adjustments to cylinder lubricant feed rates, increase or reduction, are generally made with insufficient knowledge of the cylinder lubrication conditions. Typically
the engine operator follows the engine manufacturer's recommendation, and the Chief Engineer makes adjustments to the manufacturer's recommendation based
on his own experience, current operating conditions and regular visual inspection.
Cylinder Lubricant Drain Analysis can provide information about the lubricant conditions to enable the engine operator to make
an intelligent decision about the need for an increase or decrease in the cylinder lubricant feed rates, and the degree of the adjustment.
Check and diagnose individual cylinder unit wear on a frequent and regular basis
Current practice is to calibrate the liners at the time of overhaul of a cylinder unit. This may be done with a frequency of 7,000 to 15,000 hours. The iron content
in cylinder lubricant drain samples provides a quick and economic check on wear conditions and can be carried out with a frequency according to need but typically
every 800 to 1,200 hours,
Extend the life-span of Cylinder Liners by micro-adjustment of the lubricant feed rate
Maintenance of low, but adequate, cylinder lubrication helps maintains piston cleanliness and reduces ring and liner wear.
It is a commonly held falsehood that over-lubrication minimizes the wear of the liner. It is now accepted by engine makers and by many operators that over-lubrication
can CAUSE WEAR.
Even if it were true the cost of the lubricating oil would need to be balanced against the replacement cost of the liner, such that a liner could be planned to
require replacement at 70,000 hours, or about 10 years. Comparison of lubricant costs and cost of liner replacement may suggest accepting higher wear rates with
a view to replacing liners more frequently, e.g. at 50,000 hrs.
Analysis of the cylinder lubricant drains can provide information to allow reduction in lubricant consumption and overall operational costs savings.
Plan engine cylinder unit maintenance according to condition and need
Analysis of cylinder lubricant drain samples can indicate small changes in combustion and lubrication conditions and when viewed together with Engine Performance
and Diesel Engine Analyzer data can indicate whether or not a cylinder unit requires maintenance or overhaul. By providing a trend of the engine conditions, drain
analysis can also predict deterioration of combustion and lubrication conditions and allow estimation of when maintenance will be required.
Adjust lubricant feed rates to allow for high and low sulphur fuels
The amount of acid condensation on the liner wall varies according to the sulphur content of the fuel, the temperature and pressure of combustion, and to the skin
temperature of the liner.
The increasing amount of acid which condenses on the liner wall is the main reason for the increase in cylinder lubricant feed rates over the past 15 years. The
average sulphur content in marine fuels has not increased over this period of time. However the increase in combustion temperatures and pressures has raised the
dew-point of the acid such that condensation takes place at liner wall temperatures as high as 250 degrees C, whereas earlier theory was that there was no condensation
above 190 degrees C.
Sulphur content in the fuel also affects the amount of acid condensation - a fuel containing 3.5% sulphur will therefore produce more acid than a 2.0% sulphur fuel.
Cylinder Lubricant Drain Analysis will indicate the amount of reserve alkalinity when operating on different fuels and allow
a ship regularly bunkering lower sulphur fuel to operate safely with a lower cylinder oil feed rate than one bunkering high sulphur fuel.
Fine-tune cylinder lubricant feed rate for low load or high load operation
For a given fuel the amount of acid condensation is proportionate to the engine operating load.
The amount of acid which condenses on the liner wall of an engine operating at 95% MCR will be greater than the same engine operating at 85% MCR. Cylinder lubricant
feed rate should therefore be adjusted for higher or lower load operations.
However the amount of acid which condenses changes considerably more than that due to changes in fuel consumption for higher load and lower load conditions.
The higher operating temperature and pressure of a higher loaded engine causes an increase in the dew-point of the acid, and conversely, the dew-point reduces at
lower engine loads.
Cylinder Lubricant Drain Analysis will allow the operator to adjust the cylinder lubricant feed rate for periods of high or low
load operation.
Check the efficiency of water separation from the scavenge air
Water is removed, more or less completely, by the water separator and remaining water enters the cylinder entrained with the scavenge air. In conditions of high
ambient humidity the water separator may not cope, or, if the drain becomes blocked, the amount of water entrained with the scavenge air and entering the combustion
chamber will increase.
The presence of water in the combustion chamber is undesirable as large amounts of water will cause emulsification of the cylinder lubricant and disruption of the
lubricant film with the consequence of abrasive wear.
Cylinder lubricant drain analysis alerts the operator when the water content is high. This allows the operator to make necessary
checks to identify the source of water ingress and rectify it.
Monitor performance of stuffing box and identify leaking piston glands
Due to piston rod wear or bad alignment of the piston rod gland, cylinder lubricant can leak down into the engine sump causing contamination of the system oil with
consequent risks of under-piston fouling and piston crown burning.
At the same time system oil leaks into the scavenge space resulting in increased system oil consumption and operating cost.
Evidence of leakage will be found by analyzing the cylinder drain oil and pinpoint for the operator the leaking units.
Obtain information about combustion conditions
Different marine fuels have different combustion characteristics in terms of ignition quality and combustibility. A poor quality fuel may not burn completely or
may burn slowly. The combustion condition of individual units in an engine may vary in terms of the efficiency of injection and atomization, Pcom and Pmax, the
tightness of the seal provided by the ring pack, and turbo-charger efficiency.
Poor combustion with blow-by indicated by the high Insolubles.
Ring seizure and blow-by
Poor incomplete combustion indicated by the high Vanadium level.
Unburned fuel and flame impingement on the piston crown.
Analysis of the cylinder lubricant drain oil allows evaluation of combustion conditions when using different fuels and comparison
of combustion conditions between individual cylinder units.
Evaluate the performance of engine modifications
Analysis of cylinder lubricant drain oil provides a method of evaluating the performance of new piston or piston ring designs, new liner materials, new cylinder
lubrication systems, modifications to piston rod stuffing boxes etc.. The results from the drain analysis can be interpreted to compare with those from the previous
condition and with other cylinder units.
Evaluate the performance of cylinder lubricants and fuel additives
Lubricant suppliers introduce new formulations of cylinder lubricant which can be evaluated in one or more cylinders of an engine. By analyzing the drain samples
the performance of the new and previous cylinder lubricant can be monitored between past experience and current or between individual cylinder units.
Engine operators are turning increasingly to the use of fuel additives to combat instability problems, which affect the efficiency of atomization, and to combat
fuel combustion problems of high MCR fuels. Evaluation of the use of the fuel additives and comparison of the performance of different products often requires extended
and expensive test periods without any guarantee that the fuel additive is suitably formulated to address specific fuel related operational problems.
The analysis of cylinder lubricant drains before, and then during use of the fuel additive allows the operator to evaluate the
performance of the fuel additive and its effect on fuel combustion, engine cleanliness and wear conditions.
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