Study On The Tribological Property Of Graphene Lubricative Additive In Low-sulfur Fuel Oil

In order to reduce the emission of SO_X from diesel engine,the International Maritime Organization(IMO)explicitly demands the use of low-sulfur fuel oil in ships.However,desulfurization means the removal of substances for antifriction and lubrication in the fuel oil,leading to poor lubricating property of low-sulfur fuel oil and abnormal wear of precise assemblies in the fuel oil system.In this paper,surface-modified graphene prepared by plasma assisted high energy ball milling is used as the lubricant additive in fuel oil so as to improve the properties of antifriction and anti-wear for low-sulfur fuel oil and study the dispersity and tribological property of surface-modified graphene additive in low-sulfur fuel oil.Using graphene prepared by CVD as raw material and oleic acid as modifier,graphene is surface modified by plasma assisted high energy ball milling.Analyses such as SEM,TEM,XRD,Raman spectroscopy and FT-IR infrared spectroscopy are conducted on the prepared graphene modified with oleic acid,the result of which shows that the modified graphene still maintains a fine lamellar structure.The layer of graphene varies from 3 to 5.The lamellar spacing of graphene increases with the insertion of oleic acid molecule,which,through esterification reaction with graphene,grafts to the surface of graphene,thus completing the surface modification.The modified graphene has a relatively stable dispersity in low-sulfur fuel oil.Using expanded graphite as raw material and oleic acid or low-sulfur fuel oil as modifiers,surface-modified graphene is prepared by plasma assisted high energy ball milling.Analyses such as SEM,TEM,Raman spectroscopy and FT-IR infrared spectroscopy demonstrate that the layer of graphene modified with oleic acid and fuel oil is 7 and 9 respectively.Graphene modified with fuel oil has a smaller and more uniform diameter.Both modifiers,due to long-chain alkane,grafts to the surface of graphene,thus completing the surface modification.The modified graphene has a relatively stable dispersity in low-sulfur fuel oil.A tribological test is conducted on these three kind of graphene additives.The results of four-ball tribological test shows that the optimal amount of surface-modified graphene added into the fuel oil is 0.003wt%,while the result of measurement of extreme-pressure properties shows that the maximum non-seizure load(P_B value)of compound oil with 0.003wt%of fuel oil-modified graphene,compared with that of base oil,increases by 39%.The result of pin-on-disk reciprocating tribological test shows that the properties of antifriction and anti-wear of the three graphene compound oils improve compared with those of base oil.For CVD graphene modified with oleic acid compound fuel oil,the friction coefficient and wear volume,compared with that of base oil,decreases by 65%and 60%respectively.The result of energy spectrum analysis on the surface of friction pair shows that the content of C on the surface of friction pair for compound fuel oil increases compared to that for base oil.It indicates that graphene due to its ultrathin lamellar structure and relatively large specific surface area,can easily enter the friction pair and gather on its surface,thus avoiding the direct contact of friction pair.Besides,the relative small van der Waals force between the layers of graphene makes it easy to shear,its lower surface roughness and higher bearing capacity also has an excellent effect of antifriction and anti-wear.A test of physical and chemistry property is conducted on base oil and graphene compound oil,the result of which shows that both the sulfur content in the above two oils meets the requirement of IMO on the use of low-sulfur fuel oil,and the viscosity as well as flash point of the oil samples conform to the corresponding national standard.The result of test on calorific value shows that the graphene additive in compound oil won't affect the combustion quality of oil sample.The atomization test of fuel injector shows that the graphene won't influence the atomization effect of fuel oil,without adverse effect on the combustion.