The reduction of sulphur in fuel oil has created many challenges for cylinder lubricating oil, experts told attendees at Riviera’s Maritime Air Pollution, Europe conference marine lubricants and additives session, sponsored by Castrol
One of the issues that has become apparent since the mandatory use of very low sulphur fuel oil (VLSFO) on 1 January 2020, is the need to compensate for the loss of properties in high sulphur fuel oil by altering the lubricating oil.
Issues reported to Lloyd’s Register’s FOBAS fuel analysis team include cylinder component damage, sludging, fuel injection equipment failure and other problems. FOBAS product manager Muhammad Usman noted that these issues are not unique to VLSFO, and occurred with HSFO, but there has been an increase in certain issues.
The number of investigations into cylinder component damage had almost doubled between November 2019 and June 2020 compared to the same period 12 months previously. Only large two-stroke engines were affected. “No problems were reported by those ships using four-stroke engines,” noted Mr Usman.
The most common problems found on two-stroke engines was scuffing on the liner and piston rings worn excessively or broken. In these instances there were no other signs, such as filter issues or unusual temperatures. Some of the affected engines had not been refitted with the recommended OEM piston rings for VLSFO operation.
Most of the engines were not electronically controlled and it was noted that no manual adjustment of the fuel injection or exhaust valve had been made for the different fuel. Mr Usman noted there was no definitive cause. “It is not clear if it was inappropriate base number, feed rate, non-adjustment to account for the ignition quality of fuel, lack of maintenance, poor operational practices, ships not following OEM guidelines, or a combination of all these factors,” he said.
As a fuel testing agency, FOBAS looked into the fuel quality, and found that on average, there is a 10% improvement over the old high sulphur fuel oils when tested under FIA conditions. This suggests, Mr Usman commented, that fuel quality is not the factor in the above operational problems. “However, there were some common denominators, such as lack of hard-coated (piston) rings, question marks over feed rate optimisation, and lack of operational adjustments when switched over to low sulphur fuels,” he said.
Ending on a positive note, he commented that cases had declined since the beginning of the year. He recommended the use of a condition monitoring tool to detect any changes that could indicate forthcoming failure.
Gulf Oil Marine technical director Don Gregory agreed that all the evidence pointed to a sharp rise in VLSFO-related incidents toward the end of 2019 and the start of 2021. He said the incidents that did occur, and might occur again in the future, could have been resolved with a switch from the BN 40 to a higher BN cylinder oil.
Working with OEM supplier MAN Energy Solutions, Gulf Oil Marine has developed a cylinder oil blending unit (COBU) to quickly manage the BN and detergency of cylinder oil. The COBU replaces the heater unit and is completely plug-and-play. It batch blends cylinder oil which could be in the system within an hour, a far faster switch than traditional cylinder oil changes of up to two days. “Conversely, if conditions in the liner are excellent, the COBU can be adjusted downwards and the portion of the more costly detergency component can be reduced, saving operating expenses,” said Mr Gregory.
Mr Gregory noted that diligent care and inspection is the key. “Frequent and thorough inspection of the scavenge liner and piston rings and high resolution photographic records should be undertaken no less than once per month,” he said, “Periodic scrap down analysis is also essential.”
Innospec manager, technical service engineer Joshua Townley gave detail on how the composition of fuels changed with the arrival of IMO 2020 low sulphur fuel oil. Compared to HFSO, there was an increase in the proportion of straight chain hydrocarbons. These paraffinics are prone to rapid oxidation when heated and or drop out as wax when cold. Innospec produces the Octamar ultra HF fuel additive to stabilise and produce a more homogenous fuel.
The other components are asphaltene aromatics which have benzene ring structures. “Asphaltenes can remain stable in a high aromatic blend like high sulphur fuel oil up to around 12 months,” said Mr Townley. “However, in a highly paraffinic blend like VLSFO, asphaltenes tend to fall out of solution far quicker. Fuel testing labs now recommend the safe storage time for these fuels is three to six months.”
Gathering data on as many VLSFO fuels as possible when they came available, led Innospec to the conclusion that the vast majority of the problems with VLSFO occurs during the handling phase. Nearly 60% of the issues found by Innospec could be termed “separation failure”. The company observed an engine failure rate of 14%. “Far higher than anyone expected it to be,” said Mr Townley.
In some cases, fuels with similar characteristics had very different burn qualities. As much as 23% of the VLSFO tested by Innospec burned slower than HSFO. “This has a significant impact on emissions,” said Mr Townley, “We have shown a 10% increase in the end of main combustion can result in a 70% increase in particular matter being released. This is something that can be overcome with some of our (Innospec’s) performance chemistry.”
ExxonMobil global marine OEM manager Steve Walker commented that IMO’s greenhouse gas reduction targets require engine builders to deliver significant efficiency improvements. This will require change and for current internal combustion engine technology, this will lead to higher operating pressures and combustion temperatures.
There will be greater stress of lubricants, said Mr Walker, and this is a path already trod by the off-highway industry and the evolution of engines in that sector in the early 2000s. “The make-up of lubricants (in that sector) is very different today from the early 2000s. Therefore, next-generation marine engines are going to need next-generation lubricants,” he said.
Another factor is the bulk nature of the supply chain for marine lubricants. The quantities of lubricating oil involved, typically delivered by barge, means there will need to be some element of backward compatibility.
“We are already seeing some changes,” said Mr Walker, “LNG duel-fuel engines have presented some challenges. Deposit control, detergency, oxidation stability and a degree of high-pressure wear protection is required. There will be much less importance on traditional areas like acid neutralisation as sulphur is taken out of fuels.”
The challenges of dual fuel and alternative fuel engines came up in the question and answers session. Panellist agreed that some element of blend-on-board, such as the Gulf Oil Marine COBU system will be a feature as operators need to manage the cylinder oils to the composition of the fuels. Operators should, if possible, alter the timing to consider the longer burn time of VLSFO. This is easier on electronically-controlled engines, but outside the scope of this discussion.
What is clear, the introduction of VLSFO requires a higher level of cylinder oil management and tracking of cylinder condition is essential. Before reaching that stage, operators need to know the fuel. As Innospec’s Mr Townley said, “Fuel efficiency starts in the storage tank and chemical treatment as part of a proactive fuel strategy has proven time and again to be the most efficient way to prevent issues around handling marine fuels. Rather than treating the symptoms of poor quality fuel, we tackle the cause.”