Paper Title
Hybrid Nano Additives as Engine Lubricants

The purpose of this study is to observe the effect of hybrid SiO2-TiO2nano additive in engine oil on friction and wear characteristics. A reciprocating test rig was used to investigate average friction coefficient under various nano additive concentrations and lubrication regimes (Stribeck parameter). Glycol was used as solvent for nano additives before mixing with engine oil in order to prevent them from oxidizing with air. Considering good dispersion and solubility, average diameters of the nano additives were preferred to be 12 nm and 10 nm for SiO2 and TiO2, respectively. Observations depicted that, nano additive concentrations over 0,1% wt. lead to increase in friction coefficient. Compared to commercial engine oil, average friction coefficient reductions of 25%, 18% and 7% for nano-lubricant were observed within boundary, mixed and hydrodynamic lubrication regimes, respectively. It was clear that, deposition of tribochemical reaction products generated by nanoparticles could yield antiwear boundary film formation between piston ring and the substrate and reduction in shear stress. On the other hand, spherical shape of nano additives provided transformation of sliding friction into rolling friction in which the contact surface area is smaller. Under specific loads, nano