TRIBOCHEMICAL REACTIONS IN VARIOUS HYDROCARBON FLUID MIXTURES

Abstract

Parasitic friction and material wear exist in all moving parts, causing about 20% in global energy loss annually. Machinery startup accounts for a major portion of this loss. This issue involves a boundary lubrication problem, where rubbing surfaces are inadequately covered by lubricating oils. Lubricating oil fluids rely on tribochemical reactions to establish metalorganic tribofilms that protect the contacting surfaces. The improved oil lubrication mechanism can ensure smooth operation, improving efficiency, and extending the mechanical component lifetime.

In this thesis, we study tribochemical reactions resulting from various fuel and oil blends. The interactions among blended additives are given particular attention. Lubrication phenomena are simulated using a ball-on-disk linear reciprocation configuration in a standardized tribological test rig, Optimol SRV5. The tribofilm growth patterns are investigated by measuring friction and electrical contact resistance (ECR), followed by a detailed surface analysis. The proposed lubrication mechanisms are verified with experimental and numerical simulation results.

Fuel lubrication studies are conducted by investigating a) lubricity loss upon the addition of multiple oxygenated compounds, b) accelerated material wear rates observed in dieselethanol fuel blends, and c) enhanced lubrication performances with carbon-based nanofluid fuels. Lubricity loss is found to correlate with: ● Extended induction periods for ECR rises, ● Reduced average electrical contact resistance values, and ● Inhibitions of protective frictional species formations (e.g., iron oxides and graphite).

The developed tribochemical reaction model advances the design of friction and extremepressure modifiers using tribo-active nanomaterials. For instance, adding carbon-based nanomaterials to fuels enhances lubrication performance by serving as tribo-active materials to accelerate tribofilm formation and by replenishing damaged surfaces. In engine oil systems, we demonstrated that the lubrication performance could be enhanced by formulating TiO2 nanoparticles modified by gallic acid esters, and polyether-based co(ter)polymers. Based on the tribochemical reaction mechanisms found in this study, we propose more designs of functionalized nanomaterials for advanced lubricant applications in future work.