Studies of Lubricant Degradation, Soot Aggregation and Soot Morphology in the Top Ring Zone of Internal Combustion Engines

A study was undertaken of the dispersancy characteristics of different detergent / dispersant additive packages in the piston ring zone of two operating internal combustion engines (single cylinder diesel and petrol) utilising top ring zone sampling. The dispersant type, treat level and detergent type of two succinimide dispersants at zero, half and full treat with two different detergents, a mixed salicylate type and a phenate / sulphonate type was studied. A blotter spotter method was developed by improving the method of spot size measurement by using Thin Layer Chromatography (TLC) plates and a TLC fluorescence scanner. This enabled an accurate measure of spot size expressed as a ratio of soot spot to overall oil front. It was concluded that, in the piston ring zone, dispersancy is almost independent of dispersant type and treat rate, rather the detergent package affords the dispersancy characteristics in the piston ring zone. A method for laser scattering particle size analysis was developed using a Malvern Mastersizer S to determine particle size distributions of the insolubles in the above diesel ring zone oil samples. Observations are that distinct particle size bands occur at -0.8/1m, 5-12/1m and >12/1m. In certain cases the clear particle agglomeration was observed in the ring zone over the course of the engine run where the -0.8/1 m size band was declining at the same time as the 5-12/1m size band was increasing. Morphology studies arising from the particle size work is also covered utilising scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive x-ray analysis (EDX) techniques to show that sub-micron (-20nm) particulates are also present with the -0.8/1 m particulates. The larger particles (> 12/1 m) were also shown (by SEMIEDX) to be a distinctly different type consisting mainly of calcium, aluminium, oxygen, sulphur, magnesium and iron. These particles are most probably sulphates of calcium and magnesium with some wear particles and originate from the detergent portion of the additive pack.