International Journal of Automotive Technology, Vol. 21, No. 6, pp. 14751482 (2020) DOI 10.1007/s122390200139z Copyright © 2020 KSAE/ 11814 pISSN 12299138/ eISSN 19763832 1475 RHEOLOGICAL AND WETTABILITY PROPERTIES OF ENGINE OIL WITH A SUBMICRON SPHERICAL CARBON PARTICLE LUBRICANT MIXTURE Abdullah Awad Alazemi 1)* , Feras Ghazi Alzubi 2) , Abdulsalam Alhazza 2) , Arthur Dysart 3) and Vilas Ganpat Pol 3) 1) Department of Mechanical Engineering, College of Engineering and Petroleum, Kuwait University, Safat 13060, Kuwait 2) Energy and Building Research Center, Kuwait Institute for Scientific Research, Safat 13109, Kuwait 3) Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907-2100, United States (Received 26 November 2019; Revised 9 March 2020; Accepted 10 March 2020) ABSTRACTThis study examined the physical and chemical properties of engine oil with a submicron-sized carbon particle lubricant mixture. Spherical carbon particles were added to engine oil to lower the friction and wear losses. In the current study, morphological and chemical analyses of these carbon particles were performed using field emission scanning electron microscopy and energy dispersive spectroscopy. The results clearly demonstrated that these spherical particles consist of a pure carbon element. In addition, the size distribution and dispersion stability of the carbon particles in the engine oil were investigated. The results revealed that the carbon particles have a diameter in the range of 200 to 700 nm, and they maintain their suspension in the engine oil for about 240 hours without using surfactants. Rheological studies were conducted to explore the effect of carbon particles on the rheological properties of the baseline oil at different temperatures and shear rates. The viscosity measurements, at temperature ranging from 5 to 60 °C, for the baseline oil and the oil-carbon particle lubricant mixture were almost identical (less than 4 % difference). Furthermore, a wettability analysis was performed to examine the effect of carbon particles on the wetting behavior of the baseline oil on a steel substrate. KEY WORDS : Solid lubricant additives, Carbon, Dispersion stability, Viscosity, Wettability NOMENCLATURE CA : contact angle, degree CS : carbon spheres s : shear strain rate, s 1 η : absolute viscosity of a fluid, Pa·s τ : shear stress, Pa 1. INTRODUCTION The manifestation of wear and friction in any mechanical system commonly results in a huge loss of energy and/or failure of the system. Thus, fluid lubricants are generally utilized to reduce the energy loss and avoid mechanical failure. Still, in some lubrication regimes (particularly, boundary and mixed lubrication regimes during transit situations), friction and wear phenomena could occur regardless of the presence of a fluid lubricant. This happens as a result of direct contact between asperities on sliding surfaces at high load and/or low speed operations, in which a very thin oil film—less than a few micrometers thick— separates the sliding surfaces (Hamrock et al., 2004). For this reason, numerous studies have been devoted to developing new lubricants with better tribological behavior. Several research studies have revealed the viable role of different types of solid nanoparticles as additives to boost the tribological performance of liquid oils (Tarasov et al., 2002; Huang et al., 2006; Wu et al., 2007; Kalin et al., 2012; Ali et al., 2019). However, their effect on other properties (such as viscosity, wettability, etc.) of liquid lubricants was not fully investigated. It is well-known that the viscosity of oils sharply decreases as their temperature increases. Since oil lubricants are subjected to different temperatures during operation, the oil viscosity is expected to vary according to the operating temperature. This change in oil viscosity could be very critical when the temperature is too high, leading to a low oil viscosity and, thus, diminishing the load-carrying capacity of the oil and resulting in contact between the lubricated surfaces. On the other hand, when an oil lubricant with a high viscosity is used to maintain the oil layer between lubricated surfaces at a high-operating temperature, high frictional losses will be experienced at a low-operating temperature as a result of *Corresponding author. e-mail: a.alazemi@ku.edu.kw