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.
Purpose -The purpose of this work is to investigate the static performance characteristics of thermohydrodynamic journal bearing operating under nanolubricants (lubricants containing per cent weight concentration of nanoparticles). Design/methodology/approach -Addition of nanoparticles in the lubricant increases lubricant viscosity. To study the effect of this variation on journal bearing, analytical models are developed for the relationship between viscosity, 0-0.5 per cent weight concentration of nanoparticles and temperature range of 300-900°C. To obtain pressure and temperature distribution, modified Reynolds and energy equations are solved by using the finite element method. The viscosity field (varies with temperature and per cent weight concentration of nanoparticles) is updated in these two equations by using the developed analytical model. The steady-state performance characteristics are computed for various values of eccentricity ratios for non-thermoviscous (viscosity of lubricant varies with per cent weight concentration of nanoparticles) and thermoviscous (viscosity of lubricant varies with per cent weight concentration of nanoparticles and temperature) cases. The lubricant and the nanoparticles used for the present work are SAE15W40, copper oxide (CuO), cerium oxide (CeO 2 ) and aluminum oxide (Al 2 O 3 ). Findings -The pressure and temperature distribution across the lubricant film in the clearance space of journal bearing and static performance characteristics are calculated. Originality/value -The computed results show that addition of nanoparticles in the lubricant influences the performance characteristics considerable in thermoviscous case than non-thermoviscous case.
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