Less than a year before the introduction of a global low-sulphur regime, there is no consensus about the damage compliant fuels may do to engine cylinders, Marine Propulsion can reveal.
Leading two-stroke engine developers MAN Energy Solutions and WinGD have contrasting views on the impact that low-sulphur fuels, including gas fuels, will have on cylinder condition. An independent expert confirmed that the wrong decision could leave shipowners facing emergency cylinder repairs or replacement, both requiring vessels to be taken off hire.
The confusion focuses on the role of cylinder corrosion in helping a lubricant film to stick to the cylinder liner wall, reducing scuffing damage. According to MAN, a controlled level of wear is desirable, while WinGD is focusing on eliminating wear from its engines.
Fuel with a lower sulphur content is less corrosive, leading MAN to suggest that there will not be enough wear once engines switch to permanently using 0.5% sulphur fuels. Head of marine and offshore sales Kjeld Aabo explained that, as a result, the company had recommended that owners should install cermet-coated piston rings if they switch to low-sulphur fuels. The ceramic-metal composite creates a harder surface than conventional cast-iron rings, leading to controlled wear.
MAN also suggests that operators increased the basicity of their lubricant “from time to time” in order to ensure there are no cylinder deposits that might cause scuffing. The company is working with lubricant providers to find a permanent solution involving oils with low basicity but greater detergency.
Winterthur-based WinGD denies that any wear is needed, or that low-sulphur fuels can lead to cylinder scuffing. It reports that it is already monitoring multiple engines operating long-term or permanently on low-sulphur fuel (and LNG) within emission control areas without any issues.
In a statement, WinGD said: “The liner surface structure we specify is a well-proven concept and should not be destroyed by any kind of wear. We measure hardly any wear on our liners in operation. We are still working hard to eliminate corrosion in order to keep the ring and liner surfaces as specified and machined for as long as possible.”
Cylinder honing and cleaning specialist Chris-Marine believes the impact will fall between the two main developers’ positions, having the worst impact on older engines that are less corrosive than newer models which feature a longer stroke and higher firing pressures.
“We are facing a large-scale experiment,” said Chris-Marine chief technology officer Daniel Grunditz. “Until now, most ships have been using low-sulphur fuels for maybe two weeks at a time. No-one knows what will happen when they run on low-sulphur oil for two or more months.”
The lack of consensus will concern shipowners who already face several fuel condition challenges under the sulphur rule due to take effect on 1 January 2020, including the suggested lack of availability and potential incompatibility of low-sulphur blends.
The challenges of compliance with IMO's low-sulphur regime will be discussed in detail during Riviera Maritime Media’s Americas Sulphur Cap 2020 Conference in Houston on 5-6 March. Book now to reserve your place.