Chemical and physical assessment of engine oils degradation and additive depletion by soot

Soot contamination in engine oil causes a significant increase in wear of engine components. Presence of soot in the engine oil is one of the most common reasons leading to an increase in oil change intervals. There are several mechanisms that affect the performance of engine oil such as oil degradation, additive decomposition and additive adsorption on soot particles. It is recommended that removal of soot contamination from engine oil can reduce wear of engine components and extend the service life of engine oil. However, removing soot particles from the engine oil can diminish the efficiency of additives in engine oils as some additives adsorbs on these particles. There is still no census on this area. Thus, this experimental study aims to investigate how removing different levels of Carbon Black Particles (CBP), commonly used as surrogate for soot, from aged engine oil influences the engine oil performance. The study reveals three main mechanisms that influence the tribological performance of the engine oil expressed as additive depletion, additive adsorption and degradation products. Removal of CBP from engine oil is expected to reclaim the oil performance. However, the results demonstrate that the performance of oil after removal of CBP is still not as good as the fresh oil. These results confirms that reclaiming the oil performance can not be achieved by just removing the CBP. Other mechanisms such as oil degradation and additive adsorption on CBP adversely affect the engine oil performance during the removal of CBP.