Tribological properties and lubricant mechanism of Nanoparticle in Engine Oil

In this paper, the wear and friction properties of surface modified CuO nanoparticles suspension in liquid paraffin have been studied. CuO (50nm) nanoparticle was dispersed at 0.2, 0.25, 2 and 3% in liquid paraffin using ultrasonic bath during 1 hour and 10 minutes for particle modification with Oleic Acid. Wear characteristics were evaluated using four-ball machine for the testing conditions of load 40kg at 1200 rpm rotation and 15 min test duration at temperature of 60-70 degrees C. The wear scar diameter (WSD) was measured by means of optical microscope. The morphologies of the worn surface have revealed that concentrations of nanoparticle were improved the friction and wear properties of liquid paraffin. The lowest friction coefficient (COF) was 0.185 obtained for a nanoparticle content of 0.2% CuO and the highest was for a 3% CuO concentration at 0.247 for liquid Paraffin + CuO without modification suspensions. In contrast after modification, the lowest friction coefficient was obtained at 3% CuO modified at 0.123 and the highest at 0.2% of CuO modified at 0.158 for liquid paraffin + modified CuO suspensions. Both type of nanoparticle suspensions at various concentration have exhibited clearly different friction coefficients. The results indicated that the higher concentrate of CuO, the better the tribological properties. All results were analysed according to the nanoparticles size and their deposition on wear scar surface. (C) 2013 The Authors. Published by Elsevier Ltd.