Lubricity is a measure of a fuel’s ability to reduce friction and wear between surfaces in relative motion. Hydro-treatment of the fuels to reduce the sulphur also removes aromatic compounds and that leads to a reduction in fuel lubricity.
Reduced lubricity in fuels can lead to increased wear of fuel injectors and pumps. Measurement of fuel lubricity helps in monitoring the quality of the fuel bunkered and avoiding costly damages to the engines.
Lubricity testing is usually performed on diesel fuels when the sulphur content is below 500 mg/kg (0.05%). The current limit for lubricity is 520µm wear scar as per ISO 8217:2010 (Method: ISO 12156-1:2018). The lubricity test method uses a high-frequency reciprocating rig, where the scar of an oscillating ball in contact with a stationary disk immersed in the fuel is measured.
Although lubricity cannot be predicted solely based on fuel sulphur content, the average wear scar diameter results at different sulphur ranges indicate that the wear results are the highest when the sulphur content is below 0.030%. This is as would be expected.
Data analysis performed on the samples tested for lubricity this year indicates that a majority of the samples (77.7%) fall below the 440µm wear scar and only 2% of the samples are above the limits (>520µm). However, 20.3% of the samples submitted are on the higher side or close to, the upper limit (440-520 µm) specified as per
the ISO 8217:2010 standard.
When the result obtained is close or above the upper limit for the test, it is recommended that the fuel is utilised with caution and a lubricity additive may need to be used in conjunction with the fuel to prevent unnecessary operational issues or possible wear damage. These results indicate the importance of testing lubricity in low sulphur diesel fuel
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