Four-Stroke Engine Experience with VLSFO: Time Will Tell

In the run up to the switchover, no effort was spared to to inform the industry about what to expect and how to prepare for VLSFO. A number of papers were submitted by a joint industry group under IMO. Information was released to the industry in 2019 by CIMAC Working Group 7 (Fuels) and ISO 8217. Several dedicated conferences were held focusing on the potential challenges of the IMO 2020 switchover. But, as Charlotte Røjgaard, Global Head of VeriFuel at Bureau Veritas, notes: “There are always teething issues when something new is introduced.”

She says most of the fuel related challenges were experienced during the first months of 2020, with the majority of all issues experienced in the fuel treatment system and not the engines. “Mostly, when fuel causes operational issues, the separators or filters are impacted rather than the engines. Different properties impact the engines. For example cat fines mainly impact the two-stroke engine, although they can also affect the four-stroke engines.

“Although we have had reports of cat fines related wear on the two-stroke engines this year, we have not had similar reports from four-stroke. Bear in mind that the cat fines related incidents seem to be correlated with tank cleaning rather than the VLSFOs themselves. The VLSFOs do not contain higher concentrations of cat fines than HSFO, but the viscosities and densities are lower. Lower viscosity and lower density means easier removal of cat fines, so the separator efficiency should be better for the VLSFOs than for the HSFOs.

“Whereas two-stroke engines are insensitive to ignition and combustion issues, four-stroke engines are more sensitive. However, the VLSFOs are more paraffinic than the HSFO. Paraffins have excellent ignition and combustion properties. We have not had a single report about ignition and combustion related incidents on the four-stroke engines operating on VLSFO.”

Although the quality of VLSFO has varied, Andreas Banck, Engineering Manager for New Technology at Caterpillar Motoren, says the company hasn’t found any significant issues with its use amongst its customers. “We are monitoring the development,” he says. “VLSFO has been on the market for about ten months now, but it is possible that we don’t have a full picture yet. That takes longer, because the time between engine overhauls usually happens on a multi-year cycle. So, it takes time to get a really good picture of what is happening with engine components and changes in wear behaviour.”

He also notes that the need to reduce the base number of lube oil has seen the development of new products. “Of course there are several lube oil trials ongoing, because manufacturers are continuously working on new lube oil types.”

While accepting that experience is still being gained with the new fuels and lubes, Banck is still watching carefully to understand how the situation is developing. Although the company issued proactive service recommendations to customers concerning the possible impact of new fuel, for example on lube oil choice, it was not possible for engine manufacturers to test the new fuels in advance. “Fuel manufacturers and fuel suppliers did not give a lot of information, so there were a lot of unknowns around these fuel types and a lot of rumours in the market about how they would behave. At the moment we are monitoring and are prepared to support our customers on request.”

Wärtsilä was involved in a lot of customer engagement in the second half of 2019 as operators prepared for the new 0.5 percent sulphur fuel, and Kai Juoperi,Chief Expert, Engine Fluids, R&D and Engineering, Marine Business, points to the experience gained from the earlier introduction of 0.1 percent sulphur fuels in Emission Control Areas in 2015. Thorough tank cleaning was recommended to minimise the risk of fuel compatibility issues, and advisories were also issued relating to fuel handling and injection viscosity.

No minimum viscosity limit has been set in ISO 8217, and Juoperi says: “We have seen ULSFO and VLSFO viscosity varying a lot, and especially in older vessels, where a viscometer is not necessarily installed in the fuel system, particular attention needs to be paid to correct fuel injection viscosity and temperature.”

Generally, four-strokes are less sensitive than two-strokes to an exact lubricating oil alkalinity level, and this area has not been a big issue for the company’s four-stroke engines which require the use of BN30 or BN40 oil with VLSFO.

MAN’s PrimeServ Lab, focused on four-stroke engines, has introduced a fuel-stability analysis of the new types of VLSFO and their compatibility with other fuels. As a result, the p-value has now become part of PrimeServ Lab’s standard, fuel-analysis program. The lab performs analyses of such fluids as fuel oil, lube oil, cooling water, lube-oil separator control samples and fuel-oil separator control samples for both stationary and marine four-stroke engines. The scope of diesel-fuel analysis has also been increased with lubricity, biofuel content and ignition delay added to standard reporting.

MAN Energy Solutions’ Director of New Technologies, Two-Stroke Sales and Promotion Kjeld Aabo contrasts the company’s experience with two-stroke and four-stroke engines. He says, with two-strokes, there has been several cases of scuffing damage to cylinder liners and high wear, but, he says, it’s not necessarily related to VLSFO, rather maintenance and tank cleaning regimes, and the number of issues has declined over the year. Fuel additives are effective in cleaning, but they reduce the cleaning efficiency of the separator, so the cat fines left in tanks can go directly to the engine. Cat fines are less likely to cause problems in the cylinder liners and pistons of a four-stroke, says Aabo, but they can pose a problem for injector nozzles on small fuel pumps.

On ignition quality, he also notes that it can potentially be a problem with VLSFO, and it’s one that is more likely to affect four-stroke engines than large two-stroke engines. “For two strokes, we just follow what is in ISO 8217 as there is a very broad acceptable range. For four-strokes, engine designers specify limits.”

Most of Rolls-Royce’s Bergen engines are currently running on conventional diesel or natural gas, with a smaller portion on VLSFO. Kjell Harloff, Senior Vice President, Engines at Kongsberg Maritime, highlighted the special attention needed to avoid leaks when using VLSFO due to low viscosity of these fuels, hence the need of cooling the fuel circuit to help mitigate this. There is also a need for additives to help increase the lubricity when using VLSFO. He says Kongsberg Maritime, exclusive partner for selling Rolls-Royce Bergen engines into the commercial marine market, has developed comprehensive technical user manuals offering guidance on all aspects of using VLSFO. “Focus needs to be on training the crew, to make them comfortable on the particularities of using VLSFO,” says Harloff.

Meanwhile, the company is looking ahead and investing heavily in initiatives relating to future fuels for the IMO’s 2030 and 2050 targets. “We want to make sure we have the best solutions to support sustainability when the market is ready,” concludes Harloff.