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Considering the environmental problems created by mineral based lubricants, exploring the possibility of the use of vegetable base oils as automobile lubricants has been a growing worldwide trend. In the present study, analysis of coconut oil as a lubricant has been carried out in the perspective of its tribological behaviour using a pin-on-disc tribometer. Copper oxide nanoparticles are added to the oil on weight-percentage basis, the variation of its friction-reduction and antiwear properties are analysed. At an optimum concentration of nanoparticles, the coefficient of friction and the specific wear rate are found to be the lowest. Viscosity of oil is also seen to increase by an increase of concentration of nanoparticles. Flash-point remains constant while the fire-point increases as the nanoparticle concentration is increased. From dispersion analysis it is seen that the nano oil is not suitable enough for long stationary applications. Surface structure of the worn surfaces obtained by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) shows that the optimum concentration of nanoparticles in this lubricant causes the roughness of the worn pin surface to reduce to a low value after sliding. Wear scar obtained in the presence of nano oil is smoother compared to that with bare coconut oil. When the level of nanoparticles increases above the optimum level, friction coefficient and wear rate are seen to increase.

Cerium oxide (CeO 2 ) nanoparticles are added to different lubricating oils together with suitable surfactants to obtain modified nanolubricants. Lubricating properties of these surfactant modified nanolubricants have been investigated using a pin on disc tribotester under boundary lubrication conditions. Coconut oil, paraffin oil and a commercial engine oil (SAE15W40) have been used as base oils for the present study. Changes in frictional coefficient and specific wear rate have been studied as a function of nanoparticle concentration in the lubricant together with an estimation of the settling trend of nanoparticles with time. Results show that the frictional force and specific wear rate decrease with increase in concentration of nanoparticles, come to a minimum at a specific concentration level and then increase, showing the presence of an optimum concentration level at which both friction and wear are the least. At this concentration level, coconut oil shows the lowest frictional coefficient and specific wear rate among the three oils studied. The morphology of the pin surfaces after sliding has been studied using atomic force microscopy, optical interferometer and SEM. When CeO 2 nanoparticles are added to the lubrication oil together with surfactant modification, settling trend and agglomeration of nanoparticles with time are reduced to a great extent compared to the case in which nanoparticles are added without surfactant modification.

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Purpose -This manuscript aims to deal with the tribological property variations of engine oil (SAE15W40) by the addition of copper oxide (CuO) nanoparticles on weight percentage basis. Design/methodology/approach -Experimental studies on the influence of CuO nanoparticles utilised as an additive in lubricating oil (SAE15W40) under boundary lubrication conditions have been carried out using a pin-on-disc machine in accordance with ASTM G-99 standard. The variation of viscosity, coefficient of friction, wear and settling of nanoparticles has been studied as a function of particle concentration in the lubricant. Findings -Results show that the frictional force and specific wear rate decrease with an increase in concentration of nanoparticles comes to a minimum at a specific concentration and then increases, showing the presence of an optimum concentration. With the increase in concentration of nanoparticles, the kinematic and dynamic viscosities, and the flash and fire points are found to increase. Originality/value -The use of CuO nanoparticles as additives to a moderate level is a very efficient means of improving the tribological properties of lubricating oils.