A Conditional approach to the tribology of RNLI marine systems.

Abstract

Lubricant degradation mechanisms in the 4-stroke heavy duty diesel engines of RNLI lifeboats were investigated. These mechanisms lead to the increased wear of main engine components, such as cylinder liners. The lifeboat application is distinct from the other marine applications from an engine lubrication perspective, since it involves infrequent engine running conditions and is often subjected to either under or over engine maintenance due to the unpredictable usage of lifeboats. This research has demonstrated the key lubricant properties which were affected by the lifeboat operations. Analysis of used lubricants was conducted such as Wear Debris Analysis (Analytical Ferrography) to identify the wear mechanism of affected tribological contacts and Nuclear Magnetic Resonance (NMR) analysis to analyse the trend in reduced effectiveness of antiwear additives. Other standard lubricant analysis technique were also performed to supplement the information about the lubricant condition. The experimental test rig involved the modification of a high frequency reciprocating tribometer (Plint TE77) to simulate piston ring and cylinder liner configuration. Boundary lubrication conditions that exist near the top dead centre region of cylinder liner were simulated in order to evaluate the tribological performance of lubricant additives. Also real-time condition monitoring of engine lubricant samples was carried out using a commercially available on-line sensing system. The obtained results from oil sensor were sufficiently promising to conduct engine level tests in lifeboat to monitor lubricant performance in real-time and build the system as part of the planned maintenance strategies of the RNLI. The work also involved recovering the tribological performance of used engine lubricants for further use at the end of their service life. Ionic Liquids (ILs) were tested as performance improving additives in used engine lubricants at engine start and running conditions using the modified Plint TE77 experimental test setup. Additional tests were conducted with different fully-formulated and mineral base oils with ILs as additives. Post-test surface analysis for wear mechanism and surface chemistry analysis of boundary antiwear films were performed to relate the chemical composition of films with its tribological performance. Obtained results demonstrated significant improvement in tribological performance of used engine lubricants. Also interference between Phosphonium ILs and existing additives in engine oils was noted. ILs effectively contributed to the boundary film formation when already present additives (such as ZDDP) are substantially depleted as seen in the case of used engine oil. The extension of service life of used engine oils can be achieved and has potential of significant savings in terms of fuel economy, engine reliability and by reduced oil consumption and drainage into the environment.