The pressure of compliance with recent shipping emissions rules on vessels operating in the North American ECA from August 1 has led to some discomfort among ship owners and operators bunkering low sulphur fuel oil in the Americas earlier this month.

Recently released data indicates a spate of low viscosity and density residual fuels from some US ports. A fair number of residual fuel samples tested by FOBAS exhibited very low viscosity and density values for the ordered RMG 380 grade fuel.

Tested viscosities ranged from 8cSt to 88cSt at 50°C while density values varied from 910.0 to 953.5 kg/m, which is considerably lower than those normally encountered for RMG 380 grade fuels. It is important to note that all fuels tested with low viscosities and densities were Low Sulphur Fuel Oils (LSFO) i.e. those with a maximum sulphur content of 1.00% m/m.

This uncharacteristically low viscosity/low density fuel trend may be an indication that with the introduction of the North American ECA-SOx, some fuel suppliers have begun trying unconventional blend components to meet the demand for LSFO. Issues that may arise from fuels being blended to meet the sulphur limit of 1.00% m/m may include increased cat fines, possible poorer ignition, combustion-related issues and perhaps even the contamination of fuels due to cutter stock being used which may strictly speaking not be appropriate for marine use such as the blending of bio-derived materials (FAME) in fuels.

At the time of bunkering, it is critical that ship owners and operators are provided with a BDN or certificate of quality of a particular fuel stem to ensure the right measure of density and viscosity characteristics are reported to the ship in order for proper onboard fuel management to be implemented by the crew onboard.

It is noteworthy that for the treatment of fuels with uncharacteristic density and viscosity properties, the tested density should be used for optimised operation of the vessel's fuel purification plant. As for viscosity, it should be ensured that the viscosity controller is working correctly on auto viscosity control mode in order to maintain correct injection viscosity at the engine inlet and to avoid any overheating of such fuels, especially during the changeover to and from LSFO.

While it is still too early to form a concrete opinion, feedback from users of the FOBAS program thus far indicates that the use of LSFO in North American ECA-SOx fuels appear not to have posed any significant problems pertaining to the fuels with uncharacteristic density and viscosity properties recently encountered, provided the right onboard fuel management precautions were taken. It remains to be seen, however, if any other issues may arise moving forward, such as fuels with undesirable high cat fine levels or in a worst case scenario, contaminated fuels due to undesirable cutter stock finding its way into LSFO in the North American ECA-SOx.

Blending priorities have changed over the years. Whereas in the past blending of fuels was initially carried out to cut viscosity and later on density (see previous blog on The Black Art of Blending), it is now driven by sulphur content, of which it has to be assumed and expected that responsible suppliers will be aware of the different blending permutations required to produce fuels that are fit for purpose and compliant with regulations.