Mix of tools required for cylinder oil optimisation

As one of the engine’s largest overheads, lubricants consume between 50% and 60% of the technical budget. Even a 0.1 g/kWh reduction in the cylinder oil dosage represents a significant yearly saving for the owner, says Steve Dye, business development manager at Parker Kittiwake.

Laboratory testing of the scrape down oils has traditionally been the primary method used to inform the adjustment of lubrication levels. Each of the oil majors provides a drain oil analysis programme; for example Exxon Mobil’s Signum Oil Analysis and Total Lubmarine’s Diagomar Care. In addition, independent providers such as Flame Marine provide detailed diagnostics.

“The main challenges of adopting this approach in isolation are two-fold,” says Mr Dye. “Firstly, useful results depend entirely upon testing a representative sample. In today’s shipping industry, skilled, reliable and experienced engineers who understand how and where to draw a sample are no longer necessarily the norm.” The second disadvantage is the inherent delay.

Electronically-controlled lubricating systems such as the MAN Alpha Lubricator, Wärtsilä’s Pulse Lubricating System (PLS) and Hans Jensen SIP system aim to inject the cylinder oil into the cylinder at the exact position and time where the effect is optimal. This enables significant reduction in cylinder oil consumption, but it is an open loop system and therefore does not provide feedback on the impact of this reduction, says Mr Dye. “As it is not an exact science, sensibly, a safety buffer is often applied.”

Offline tools include the Shell AnalexAlert, a portable device that helps monitor cylinder liner wear by providing onboard measurement and recording of metallic iron content in the scrape down oil (along with the additional capability to measure grease from gearboxes, bearings and other ancillary plant). Used on a daily basis, a standard sample bottle containing the oil for analysis is placed on the unit and, using a simple touch screen menu, engineers can obtain a reading within seconds. The Exxon Mobil Scrapedown Analyser is operated in a similar way.

“Dependent upon trade, load, running hours and other factors, constant real-time monitoring is the ultimate tool for safely optimising cylinder lube oil feed rate,” says Mr Dye. Parker Kittiwake’s LinerScan is being used by companies such as A.P. Möller-Maersk Group, Hapag Lloyd, Ernst Russ and Reederei F. Laeisz to inform feed rate reduction and achieve maximum penetration of the lubrication safety buffer.

Using magnetometry to quantify the iron in used cylinder oil, the LinerScan sensors are fitted to each cylinder of the vessel engine and report changes caused by abrasive wear, highlighting periods of increased physical or thermal stress. This provides an understanding of the factors influencing cylinder liner wear to monitor change trends and see wear developing.

“Achieving the optimal feed rate solution may rely upon the adoption of a combination of traditional and state of the art tools and techniques. It is certainly possible to simply adjust lubrication according to the OEM’s instructions, but this is risky. You may only experience the effects later on when you notice the loss of more liners, and as the average insurance claim for unexpected liner loss is over $250,000, this can be an expensive realisation,” says Mr Dye.

For Tim Roadnight, global business line leader OCM at Intertek, the multiplicity of onboard systems and on-going developments in automation mean that the analytical assessment provided by laboratories with trends reviewed by technical experts is imperative. “The key predictive maintenance techniques to evaluate would be residual TBN to new oil values and the iron level,” says Mr Roadnight. “If the level of iron in the oil is increasing while operating at a lower feed rate, then slow feed rate increments should be taken. In line with this, if the TBN drain oil drops below 10TBN the engine would need inspection for possible abrasive wear.”

When using both TBN 40 and 70 oils, problems occur with incompatibility of different fuels and this can impact on wear due to scuffing. “In respect of lubricants, it’s imperative to ensure its ability to control corrosion and wear isn’t affected with the changes. A high TBN lube in a low sulphur heavy fuel (LSF) can produce excessive hard deposits due to high thermal load on unreacted neutralising additives. Another issue of high TBN oil in a LSF environment can be reduce corrosion to such a point that the cylinder liner surface becomes too smooth, unable to hold the oil,” says Mr Roadnight.

As TBN is decreased, so is the amount of additives such as detergents and therefore its ability to minimise piston deposits is reduced. Changing feed rates can cause issues as the amount of lubricant in the cylinder may not be adequate to cover the full service and provide enough acid neutralisation. A load dependent feed rate program can be developed with the engine manufacturer or feed rate algorithms based on sulphur levels can be used, says Mr Roadnight. “With any cost saving programmes it’s imperative to monitor important properties relative to wear and optimisation feed rates. These will include iron content in the used cylinder oil sample. This said, it’s possible, if undertaken correctly, to reduce cylinder oil feed rates balancing engine component replacement cost.”