Test procedures to investigate tribo-chemical phenomena
As with any laboratory test, there is the general and not insignificant challenge to closely reproduce the tribological conditions without having to operate a large diesel engines. Simulations always leave a shadow of doubt that the conditions do not nor cannot exactly match those in the fired engine.
In the context of wear rigs, we have heard about the Shell procedures using a Cameron-Plint reciprocating wear rig, and there are numerous variants on other tribo-wear rigs e.g. Falex tests, gear rigs.
Deposit tests are often variants of the panel coker procedure. Each company tends to develop its own variants.
Neutralisation procedures were and are used both in basic studies and for developing new oils. To cite just two examples based on similar principles, there is a Shell procedure and the later Elf NAMO test, described to us this week.
Responses to water via bench or rig testing remain a target for marine engine oil developers. This should be an area of further study within the CEC IL-047 group.
Cylinder lubrication stresses
The development of the necessary state of the art products has over the years relied upon the corrosion testing the measurements of neutralisation rates and extent, by the application of laboratory engines, cooperative testing with engine manufacturers, field trials, and by the application of test procedures in the tribo-wear rigs. These are in various configurations, matching relative velocities, loads, metallurgies, temperatures with or without pre-neutralisation of the detergent base components. In other words every effort is devoted to simulating the conditions, or at least some of them, in the fired engine. Only the latter can create the dynamics of the real ring liner system or of the bearing load patterns and for vessels at sea, even the extent to which the healing of the ship and tilting of the engine may influence the loads, oil film thicknesses and subsequent wear patterns. [cp elegant studies by Dr S. Moore of BP - CIMAC 1995]
In the trunk piston engines an important aspect of performance is controlled oil consumption. In distillate fuelled engines problems have occurred, linked to certain applications and/or geographical regions. Loss of oil consumption control is attributable to bore polish or liner lacquer. The advent of flame rings and their introduction to certain more sensitive engine designs has eliminated the bore polish aspect. Whether lacquer may still be formed is being considered. Nevertheless, studies in a laboratory engine have indicated possible causes for liner deposits and identified alternative solutions based on oil formulation routes, as indicated. The CEC IL-047 group is still monitoring the situation from an industry-wide perspective.
To put some substance into this challenge for advancement in lubrication we have studied the problem of lacquer formation using laboratory engines of representative scale. In summary the studies have enabled us to postulate mechanisms that can be tested. A set of contributory factors is presented, some or all of which may be involved in genuine field issues of loss of oil consumption control. With the lab. engine we have been able to test experimental oils that do respond differently with respect to liner cleanliness ratings. To illustrate this, one slide covers the lacquer ratings measured for five different formulations. Ratings are split such that the upper 25% swept area is calculated separately from the remaining 75%, and then recombined for the overall cleanliness assessment. The principal target is to achieve the minimum deposit in the upper region. With oil E, for example, that target has been met. The remaining primary challenge is to ensure the one cylinder data are substantiated in multicylinder engines operated over thousands, not hundreds of hours.
Additional Modelling of lubrication
・oil film thicknesses as functions of crank angle, dimensions of components, pressures, engine speeds, locations e.g. bearings, piston/liner, ...
・modelling of the complete combustion process, chemically physically and mechanically
Advances in tribology
A major Tribology Conference in Nagasaki follows the ISME meeting - the latest progress will be presented there, for active researchers to study in the years to come.
STLE in USA is another source of information, often of a practical nature.
The Leeds - Lyon Conferences on Tribology also provide a great wealth of research orientated information.
I have deliberately concentrated on the practical aspects in this summary presentation in order to relate the end user experiences back through to the efforts of the fuel delivery chain, the lubricant formulators and to the chemists developing new additives so essential to enhance the inherent properties of base fluids.
The challenges are becoming clearer for this next decade, century and millenium that lubricants of the highest quality of performance are essential. This will be achievable with the new additives, base fluids and inventive skills of formulators working in cooperation with the equipment manufacturers and users.
Acknowledgement
The author wishes to thank Shell Marine Products for permission to deliver this presentation.
One final, personal comment that in keeping with the Japanese concept of retirement, in three months time l become a‘wet leaf’, so difficult to sweep from the patio tiles.
