Frequent inspections of engines is essential, says WinGD’s Konrad Räss, who recommends fuel handling and changeover procedures be implemented
At Riviera’s Asian Sulphur Cap 2020 conference held 15-16 October in Singapore, Winterthur Gas & Diesel’s director for R&D Konrad Räss said its engines were robust machines and required no intervention in the hardware if the properties of the fuel at the inlet to the engine are maintained as per specifications.
WinGD components from fuel injector, lubricator, piston and piston ring are designed to survive in zero sulphur fuel and high sulphur fuel, said Mr Räss. “On the hardware side, we don’t foresee any changes. A full chrome ceramic coated piston ring pack (all rings with same coating), for instance, has been the standard in our engines for more than 12 years,” said Mr Räss. The sulphur mandate is more a chemical issue that should be handled with a correct lubricant, he added.
As far as the lube oil is concerned, WinGD specifies BN 40 to 60 for 0.5% sulphur fuel. BN 70 to 80 oil can be used down to 0.1% sulphur but care must be taken, he said. “In general, with new fuels, nobody knows exactly how they are going to behave since the variety of fuels is expected to be huge. Regular inspections are a must, especially in the initial period,” he said, adding that the viscosity for distillates must be a minimum of 2 cST at the inlet of the engine. For residual fuels, it should be 13 to 17 cST, he said.
The sulphur cap as well as upcoming IMO mandates may well trigger a new trajectory for engine development. Alternative fuels including LNG are likely to be used widely.
“If 0.5% would the maximum all over the world, we could update our lubricant recommendation list,” said Mr Räss. “But we should not forget that with 0.5% we still have a corrosive environment in the combustion chamber. That means liner wall temperatures for example would need to stay well above the dew point of water.”
Changes in properties
A WinGD guidelines document on Very Low Sulphur Fuel (VLSF) states that the VLSFO must be compliant with ISO 8217:2017 and fit within the same RM grades as used before 2020. However, fuels of the same ISO grade may show a high variability in other characteristics. It is expected that VLSFO will have similar properties to ULSFO. The following parameters might change with new VLSFO fuels: compatibility and/or stability, viscosity, cold flow properties, calculated carbon aromaticity index (CCAI), and catalytic fines concentration.
Depending on the origin and production process used, VLSFO can be predominantly aromatic or paraffinic in nature. This could lead to compatibility problems between different fuel batches even if they are within the same ISO 8217:2017 fuel grade. Blending of aromatic with paraffinic fuels on board might result in sludge formation (after prolonged time in a tank, even if initially stable) due to a change in solubility properties of the resultant blend in comparison to original fuel batches.
In VLSFO containing high fractions of paraffinic components, exposure to prolonged cold conditions may lead to wax formation, which in turn could affect the cold flow properties of the fuel. Therefore, before obtaining a fuel, it is recommended to make sure that the fuel cold flow properties comply with the fuel system design and the planned ship routing. Additionally, for residual fuels with low viscosity it is recommended to keep the fuel at 15°C above the pour point.
The CCAI provides an indication of the ignition properties or ignition delay of the fuel on the basis of fuel viscosity and density. In view of the broad range of density and viscosity values of VLSFO, resulting CCAI values can also vary considerably. However, as long as the CCAI limits as defined in ISO 8217:2017 are fulfilled, WinGD engines can be operated without any limitations.
The level of cat fines in VLSFO is unknown and might vary depending on the refinery streams from which the fuel was produced. It is highly recommended to follow ISO standards and WinGD recommendations regarding cat fines, which includes running the fuel purification system at high efficiency level.
"Will the fuels leave more or less deposits on combustion chamber components than seen today? Will each bunker batch be different? These are the questions," said Mr Räss.
Mr Räss said that today’s compliant fuels had not produced any abnormal liner and piston ring wear rates on engines during testing with current standard fuels, but that lubricant feed rates and grade may need to be adjusted for the 0.5% sulphur fuels.
New fuels are likely to be more paraffinic than aromatic, he explained, care must be taken for the correct storage temperature so that paraffinic fuels cannot block filters. Sulphur cap-compliant fuels may also precipitate catalytic fines upon blending of different batches of fuel, he said.
Mr Räss recommended operators using more fuel tanks and settling tanks to avoid mixing bunker batches in the tanks. A splitting of existing larger tanks is a possible solution to store more fuel types, he advised. This would ensure that two oil batches are stored at different temperatures, given that viscosity is expected to vary among the different low-sulphur fuels.
Ideally, according to Mr Räss, two bunkers should not be blended on board. Fuel suppliers have greater control over the blending process and the outcome of fuel properties than crew on board vessels. If ship staff have no option but to mix bunkers from different suppliers, he said, then the standard spot test could provide useful inputs. Mr Räss said samples of 50-50, 40-60, and 90-10 blends could be tested. A spot test would give an indication of the stability of the blend at the different mixing ratios.
Following his presentation at the conference, Mr Räss faced a volley of questions from attendees regarding operating with compliant fuels.
One questioner wanted to know if a bunker contaminated with chemicals could crack piston rings, noting the same fuel did not cause sludge. Mr Räss said a worn liner combined with high pressures could break piston rings and the nature of the contamination could create those conditions.
Another questioner asked about changes needed when running an engine on low load. Mr Räss said no changes are required to the engine or its procedures.
WinGD’s changeover recommendations suggest a fuel management procedure (suited to the specific fuel system in use) should be prepared in order to minimise the mixing of fuels from different batches during fuel changeover. Before filling the settling tank with a new batch of fuel, it should be ensured that the tank is empty. If a settling tank contains unused fuel when filling it with a new batch of fuel, the tank should be drained frequently to check for possible sludge accumulation. The service tank should be empty before filling it with a new batch of fuel. If it is not possible to empty the service tank completely, the quantity of previous fuel remaining is to be kept to an absolute minimum.
Onboard staff should check the viscosimeter is working properly and adjust the temperature accordingly to reach the specified engine inlet viscosity. This temperature adjustment should be carried out at a maximum rate of 2 °C/min.
Care must also be taken to the temperature adjustments at separator, since these temperature requirements change with the fuel’s viscosity.