Richard Fiifi Turkson

Enhancing the thermophysical properties and tribological behaviour of engine oils using nano-lubricant additives

This paper presents the enhancement of the thermophysical properties (thermal conductivity and viscosity) of engine oil using nano-lubricant additives and a characterization of tribological behaviour in terms of sliding contact interfaces (piston ring assembly) in automotive engines. Al2O3, TiO2 and Al2O3/TiO2 hybrid nanoparticles were suspended in commercially available engine oil (5W-30) in a concentration of 0.25 wt% for formulating nano-lubricants. The sizes of Al2O3 nanoparticles were within the range 8–12 nm while the TiO2 nanoparticles used had a size of 10 nm. The tribological experiments were performed using a tribotester to simulate the sliding reciprocating motion of the piston ring/cylinder liner interface in an engine. The performed tribological tests were all carried out under varying speeds, loads and sliding distances. The experimental results showed that nano-lubricant additives enhanced the thermophysical and tribological properties. The thermal conductivity of lube oil was measured by the 3ω-wire method. Nano-lubricants provide low kinematic viscosity and an increase in the viscosity index by 2%. Meanwhile, thermal conductivity was enhanced by a margin of 12–16% for a temperature range of 10–130 °C facilitating the dissipation of frictional heat and maintaining engine oil properties, as compared with commercial lubricants. The tribological tests showed a minimization of the friction coefficient and wear rate of the ring by 40–50% and 20–30%, respectively. According to the results, nano-lubricants can contribute to improving the efficiency of engines and fuel economy in automotive engines.

An analytical study of tribological parameters between piston ring and cylinder liner in internal combustion engines

This paper presents a model to study the effect of piston ring dynamics on basic tribological parameters that affect the performance of internal combustion engines by using dynamics analysis software (AVL Excite Designer). The paramount tribological parameters include friction force, frictional power losses, and oil film thickness of piston ring assembly. The piston and rings assembly is one of the highest mechanically loaded components in engines. Relevant literature reports that the piston ring assembly accounts for 40% to 50% of the frictional losses, making it imperative for the piston ring dynamics to be understood thoroughly. This analytical study of the piston ring dynamics describes the significant correlation between the tribological parameters of piston and rings assembly and the performance of engines. The model was able to predict the effects of engine speed and oil viscosity on asperity and hydrodynamic friction forces, power losses, oil film thickness and lube oil consumption. This model of mixed film lubrication of piston rings is based on the hydrodynamic action described by Reynolds equation and dry contact action as described by the Greenwood–Tripp rough surface asperity contact model. The results in the current analysis demonstrated that engine speed and oil viscosity had a remarkable effect on oil film thickness and hydrodynamic friction between the rings and cylinder liner. Hence, the mixed lubrication model, which unifies the lubricant flow under different ring–liner gaps, is needed via the balance between the hydrodynamic and boundary lubrication modes to obtain minimum friction between rings and liner and to ultimately help in improving the performance of engines.