Cylinder oil consumption monitoring is one of the main drivers for fleet performance management. Savings between 4% and 7% are regularly found, in some cases up to 25%.
Fleet performance management targets the whole ships efficiency and it’s improvement. The first measurable indicator and with highest priority for success is the overall fuel oil consumption reduction, but high global fuel oil prices have an impact on the lubes as well. The cylinder oil consumption for two-stroke prime movers is worth reviewing.
The analysis of ECO Insight data revealed 4% to 7% savings in cylinder oil consumption of customers fleets over time. The calculated savings are the difference between a reference period close to the implementation of ECO Insight and today (beginning of 2018).
Watching is not enough
The savings are not generated automatically just by watching the cylinder oil consumption. First the reported measurement need to be monitored and compared to target figures. The target ranges for a conventional lubricator from 1 to 1.6 g/kWh and for an advanced lubricator from 0.5 to 0.9 g/kWh.
Average figures can be checked on regular (monthly) basis and Performance Center customers are alerted additionally ship specific on a regular (daily) basis for each ship.
Over consumption is not only expensive, because a lot of unused oil will escape in the scavenge area, but can have other negative technical impact. For example, excess lube oil can result in piston rings sticking in the ring groove, prevent rotating, and combustion gas blow by.
Under consumption must be avoided to safeguard the purpose of cylinder oil: (a) maintain an oil film between piston rings and cylinder liner, (b) avoid corrosion by sulfur content in fuel oil and (c) clean cylinder liner from combustion residues.
Effect of Feed rate change
Fine tuning of the lubricator is a continuous process, which can be re-initiated by informing crew and technical incharge, if the values found out of range. Visual inspection of cylinder liner and piston condition through the scavenging ports should also be carried out per the manufacturer’s recommendations, but also to ascertain the effect of changes in cylinder oil feed rate or cylinder oils.
Lubrication rate might be increased after the change of cylinder liner and piston or due to the demand on the sulfur content in fuels. If not two or more lubricants in stock, the lubricator needs to be adjusted, when sailing within and outside of sulfur emission control areas (SECA). For example: Lubricants with a base number of BN70 to BN100 for fuels with sulfur content of about 3.5% have been in use in the past. Today and in future most likely BN40 (or below) are used for fuels with sulfur content of about 0.5% down to 0.1%.
Even with the sulfur cap in 2020, still different cylinder oil lubricants will be in use to support different fuel qualities on globally trading ships.
Benefit of optimized feed rate
Unlike many other vessel performance levers, which are about fuel consumption, lubes consumption is directly on ship owners account and ship owners will benefit from the savings. Benefits are the direct lubes reduction but also less engine maintenance, when the feed rate is optimized.
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Source: DNV GL