Technical Committee Lubricants

Effects of Soot and solid foreign Matter in used Lubricants on the Wear-behaviour of modern Diesel Engines with prolonged Oil-drain-intervals

Wear- and friction measurements in a tribometer showed less friction and higher wear rates compared to fresh oils. Instabilities appeared more frequent with higher soot levels. Surface- and particleanalyses revealed, that tribomutated areas from soot-oil-experiments contain less concentration of oil additive elements and present a finer microstructure of the surfaces. On many sootparticles an amorphous, probably additive-containing layer was found. Studies on a microtribometer revealed, that oil-soot is not hard or acts abrasive. In centrifuged oils less concentration of additive-elements were measured and they tend to more wear and instability. In the following investigations on a cam and tappet test stand the tribological results were widely confirmed and so the tranferability of tribometer experiments to the real system was prooved. Based on the results, models for the mechanisms of influence of soot on tribological behaviour were formulated, building the fundament for lubricant modifications. They were driven in an engine test in order to check out the models.