Lube-Tech
The results of this fuel and lubricant testing are discussed below and demonstrate how functional additives can effectively reduce the impact of fuel variability, with improved performance in the area of engine deposit control - aspects which contribute to improved engine durability. This goes beyond conventional cylinder oil formulating and demonstrates ‘BN’ (Base Number) alone is not the answer for these 0.5% sulphur fuels.
Fuels study
Shortly after the implementation date for the sulphur cap reduction was confirmed, concerns about the quality of 2020 compliant fuels began to be voiced. These concerns focussed on compatibility, stability, combustion characteristics, viscosity and pour points. The purpose of undertaking a fuels study was to try to validate the concerns and understand the implications they could place on lubricant performance requirements.
Without access to samples of very low sulphur fuel oils (VLSFOs) currently under development, commercially available 0.5% w/w sulphur fuels from China have been supplemented with a range of in-house laboratory blended VLSFOs. These laboratory blends have been derived from globally sourced high sulphur fuel oils (HSFOs) and the appropriate amount of distillate to achieve 0.5% w/w sulphur content. In total 5 commercially available VLSFOs and 5 laboratory blended VLSFOs were assessed.
Compatibility concerns relate to the co-mingling of incompatible bunkers on board vessels and can be managed through tank segregation until compatibility can be confirmed through testing. Stability refers to each individual fuel oil being a stable product. A contributing factor underlying both issues is asphaltene stability. Asphaltenes are present in all crude petroleum residues but vary in content and characteristics depending on the origin of the crude oil. Asphaltenes are high molecular weight polar
36 LUBE MAGAZINE NO.153 OCTOBER 2019
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.124 page 3
molecules, predominantly aromatic in structure. Asphaltenes are sensitive to changes in the aromaticity of the total fuel matrix which changes on blending. Combining with a paraffinic refinery stream such as a low sulphur distillate to reach 0.5% w/w sulphur fuel would therefore increase the risk of the final blend being unstable. This instability could impact other characteristics of the fuel such as combustibility and the deposit forming tendency. The composition of fuel can be characterised by determining the quantity of Saturate, Aromatic, Resin and Asphaltene fractions (SARA). These fractions are each associated with asphaltene stability and thus this technique could be useful in identifying fuels with the potential for stability issues.
The stability of the commercial sourced VLSFOs was probed further using a proprietary bench test that gives a quantitative assessment of stability. The three most unstable commercial VLSFOs were then tested with two additives: Additive 1 is a detergent known to be effective in deposit control and asphaltene stabilization; Additive 2 is a Lubrizol novel dispersant known to be effective in deposit and varnish control and asphaltene stabilisation. Figure 1 shows the novel dispersant was the most effective in stabilising the fuel so it should show good dispersancy of deposits in the combustion zone.
Figure 1: Lubrizol novel dispersant significantly increased fuel stabilization in each of the three most unstable VLSFOs tested.
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