Yes / The presence of lubricant droplets in the gas that flows through the piston assembly and crankcase of an internal combustion engine (generically termed oil misting) has important implications for performance, particularly lubricant supply to the upper piston assembly, oil consumption and lubricant degradation. A significant source of these droplets is thought to be oil shearing and blow-through by blow-by gas flows in the piston assembly. An experimental rig was developed to simulate the high velocity gas and lubricant film interactions at a top piston ring gap where the flow conditions are most severe. Flows of lubricant droplets were produced and characterised in terms of the proportion of the oil flow that formed droplets in the gas flow and the size distribution of the droplets produced. Considering various aspects of a commercial automotive crankcase formulation, the effect of lubricant viscosity was found to be particularly important. Of the lubricant additives evaluated, viscosity modifiers were found to have the greatest effect on the tendency to form droplets: Detailed study on a range of viscosity modifiers identified that the influence of their molecular architectures on viscoelasticity was the key mechanism.

Yes / The tribological performance of the piston assembly of an automotive engine is highly influenced by the complex flow mechanisms that supply lubricant to the upper piston rings. As well as affecting friction and wear, the oil consumption and emissions of the engine are strongly influenced by these mechanisms. There is a significant body of work that seeks to model these flows effectively. However, these models are not able to fully describe the flow of lubricant through the piston assembly. Some experimental studies indicate that droplets of lubricant carried in the gas flows through the piston assembly may account for some of this. This work describes an investigation into the nature of lubricant misting in a fired gasoline engine. Previous work in a laboratory simulator showed that the tendency of a lubricant to form mist is dependent on the viscosity of the lubricant and the type and concentration of viscosity modifier. The higher surface area-to-volume ratio of the lubricant if more droplets are formed or if the droplets are smaller is hypothesised to increase the degradation rate of the lubricant. The key work in the investigation was to measure the size distribution of the droplets in the crankcase of a fired gasoline engine. Droplets were extracted from the crankcase and passed through a laser diffraction particle sizer. Three characteristic droplet size ranges were observed: Spray sized (250–1000 μm); Major mist (30–250 μm); and Minor mist (0.1–30 μm). Higher base oil viscosity tended to reduce the proportion of mist-sized droplets. The viscoelasticity contributed by a polymeric viscosity modifier reduced the proportion of mist droplets, especially at high load.

[pt] Dentre os aditivos empregados nas formulações de óleos lubrificantes, cabe destacar os de natureza polimérica, utilizados como melhoradores de viscosidade. Atualmente, testes complexos e de alto custo são empregados para avaliação de novos componentes nos óleos lubrificantes. Portanto, análises preliminares para estudo e caracterização de aditivos são de extrema relevância. Este trabalho tem como objetivo caracterizar diferentes polímeros, utilizados como modificadores de viscosidade, empregando métodos de análise térmica e reológica, e ainda avaliar o impacto destes aditivos em bases lubrificantes. Os resultados encontrados permitem avaliar o comportamento das borrachas poliméricas frente à degradação térmica, influenciada pelo processo de polimerização e estrutura química, e frente ao seu comportamento reológico mostrando ser uma metodologia eficiente para diferenciação destes materiais. As bases lubrificantes avaliadas mostraram um comportamento de fluido newtoniano clássico e quando os polímeros modificadores foram adicionados, em determinadas concentrações, observou-se uma alteração deste comportamento de fluido. As análises e técnicas empregadas permitiram avaliar o impacto no comportamento reológico dos óleos básicos bem como das soluções preparadas com diferentes concentrações de polímeros. Foi possível concluir que os aditivos poliméricos empregados em bases lubrificantes são capazes de alterar o comportamento térmico e reológico das bases lubrificantes estudadas. As metodologias empregadas se mostraram eficientes para avaliação preliminar destes polímeros e das bases lubrificantes contendo estes aditivos. / [en] The most important additives used in lubricant formulas are polymeric in nature, which play an important role in the performance of the fluid and act as a viscosity modifier. Due to the fact that lubricants with lower viscosities are higher in demand, the viscosity modifier function has become increasingly important and differential in lubricant formulas. In order to develop new components of technology for lubricants, complex tests, which are high in cost, are necessary. Therefore, preliminary analyses of new studies and the characterization of new data are extremely relevant and important for the customization of the process and timing. The intention is to characterize polymers available on the market as viscosity modifiers using thermal and rheological methodologies, as well as to have a better understanding of the influence of these additives on base oils used in lubricants. The results showed the polymers behaviors on thermal degradation, which are influenced by the polymerization process as well as chemical structure. Rheological analyses demonstrated to be an efficient methodology for the differentiation of these materials. Base oil study results showed the Newtonian fluid behavior and this was modified when substantial amount of polymers were added. The rheological and thermal behaviors of base oils as well as solutions with polymers in different treatment rates were realized by the analyses and techniques executed. For the preliminary evaluations of polymer additives and base oils with them, the methodologies used in this study proved to be efficient.

The increasing demand for more readily bio-degradable, renewable and non-toxic environmentally adaptive lubricants with a lower degree of bioaccumulation has escalated the investigation of water-based lubricants as the potential alternatives for conventional mineral-based oils. Water is an excellent environmentally adapted lubricant; however, it is a low viscous fluid and holds downsides of having corrosive nature and extremely low pressure-viscosity coefficient leading to insufficient load-carrying capacity. These shortcomings make pure water a poor choice for operations involving high load and low speed, for instance, within hydropower applications. Therefore, the choice of appropriate modifiers and additives is crucial to improve the viscosity, friction-reducing performance and anti-wear properties of water as a base lubricant. Appropriate selection and combination of bearing materials also significantly improve the tribological performance of the lubricants. In the presented work, tribological behavior of polyvinylpyrrolidone (PVP) and poly(sodium 4-styrenesulfonate) (PSS) thickening agents with water as a base fluid in the lubrication of pure UHMWPE and SCF reinforced UHMWPE bearing materials has been investigated individually under reciprocating tribometer. The results showed that both PVP and PSS are excellent viscosity modifiers. PVP exhibited excellent friction-reducing and anti-wear performance, while PSS revealed increased wear rates with an insignificant reduction of friction coefficients. This study aims to explore the potential for using newly developed water-based lubricants in the replacement of traditional mineral-based lubricants for hydropower turbine bearings.