Bridging macroscopic lubricant transport and surface tribochemical investigations in reciprocating engines

Abstract

Engine design studies are often conducted with one of two distinct focuses on two different scales: overall engine analysis or localized surface analysis. However, recent engine research requires a more combined approach. Classical tribological experiments and models have been developed usually for general contacting surfaces under specific operating conditions. They attempt to simulate the actual engine environment, which varies significantly with component design and engine operating conditions. Macroscopic engine studies, on the other hand, yield information pertaining to the overall engine system, such as component dynamics, lubricant flow, pressures, and temperatures. These macroscopic operating parameters serve as boundary conditions to the localized surface or tribochemical problem. This paper discusses the macroscopic oil transport processes in the engine and presents several current engine performance problems, such as in friction reduction, modelling wear with antiwear tribofilms, and minimizing deposit formation and emission of ash-related species. It also illustrates applications of the combined analysis of bulk oil transport in the engine with material surface phenomena and tribochemistry. A specific example involves the oil supply to the piston ring-pack and changes in oil and additive characteristics in that region.