Brian Østergaard Sørensen, vice president, head of research & development two stroke, MAN Energy Solutions, explains how to overcome equipment concerns in relation to the upcoming sulphur cap
We have closely studied various facets of the 2020 sulphur cap and the change-over to low-sulphur fuel in many of our engines. We have issued detailed service letters to our users on how best to manage the change-over.
We procured some of the most difficult of such fuels in the market and ran them on our test engines to characterise the combustion. We found that ignition was not really an issue on our two-stroke engines. For medium-speed engines it may be an issue due to the shorter time for ignition and combustion at higher rpm. We have concerns about other aspects such as cleaning of the bunker tanks, use of blends, and mixing the bunkers from various sources.
In one of our service letters, we described how we tested samples of fuels from different sources and found that they varied widely in properties such as in viscosity, pour point, density and the levels of cat fines. We told users to avoid mixing different fuel batches, while paying attention to the actual fuel parameters. They should adjust the fuel temperature to ensure correct viscosity, which may vary within the fuel batch. This would mean keeping viscometers operational.
On cylinder lube oil, we advise that the operating engineers should check the cylinder condition frequently and ensure that the piston ring pack is clean and moving freely. In case of deposits, they should use oil with higher detergency. For fuel of maximum 0.1% the general guidance is 15-25 BN while for 0.1% to 0.5%, it is 40 to 70. The target is to minimise the cylinder oil feed rate yet maintain acceptable cleanliness, acceptable wear and avoid hard contact, such as micro-seizures on the piston rings and cylinder liners.
We have asked that cat fines levels should be carefully monitored and kept below 15 ppm. Cat fines can be removed from the fuel by setting a high temperature (min. 98°C) and a low flow in the fuel separators. The tanks in service should be cleaned properly by making the overflow pipe in the service tank go to the bottom of the tank, and by using a separate line to recirculate the fuel to the settling tank. We have said that a 10 µm abs fine-filter should be installed in front of the engine and alarms should be set to go off in case of abnormality.
During the process of cleaning the bunker tanks, there is a proposal to use additives to get the sediments to float in the fuel. This would concentrate the cat fines and if they get into the engine they could increase the wear. There could be cat fines in the blends that will come in as bunker.
The fuel treatment process as well as the fuel handling equipment, such as the purifiers, should be properly dimensioned and well maintained; otherwise, we could see a spike in the wear.
There is a logistical challenge of handling various bunkers coming in. In the past, bunkers from different vendors were similar and could often be mixed. Now they may be like human blood types or oil and water; they cannot be mixed.
The low sulphur fuel or operation in gas may increase liner scuffing because the lubricity of these fuels is lower than heavy fuel oil. We recommend that operators of our engines replace their piston rings with those with hard cermet coating on the running side to mitigate the problem of liner scuffing.