عنوان مقاله [English]
Using an appropriate lubricant is a vital issue for systems like internal combustion engines that they are constantly exposed to friction and wear due to the relative movement of their own components. Since improving properties of engine oil affects the better performance of engine, the addition of nanoparticles is proposed as a solution. Nanoparticles used in this study are Al2O3 which are polar in spite of their excellent characteristics like high thermal conductivity and high wear resistance. In this study, oleic acid is employed as a surface modification agent to prolong the dispersion stability of nanofluid. To examine the effect of nanoparticles size and viscosity of base fluid on dispersion stability of nanofluid, alumina nanoparticles were purchased and surface modified in two particle size of 40-60 nm and 20 nm and they were dispersed in engine oil as base fluid with viscosity of 20w50 and 10w40, both at the same concentration of 0.1wt% as the time passed the samples were photographed and results revealed that nanofluid sample made of 20w50 base fluid and nanoparticles of 40-60 nm exhibited the longest stability of 36 days. The discussed additive powder becomes super fine after surface modification which increases their tendency to agglomerate and precipitate and also the lower viscosity of base fluid which indicates its lower inner friction that will not prevent the precipitation of nanoparticles, are the reasons of lower dispersion stability of other nanfluid samples.