Effect of soot properties in diesel engine oils on frictional characteristics

Physical and-chemical characterizations of soot in diesel engine oils are conducted to investigate the impact of soot properties on friction coefficient between reciprocating rubbing metal surfaces. In SRV function tests, soot in an engine oil categorized in API CG-4 appeared to act as friction modifiers, since a higher content of soot in the oil caused lower friction, especially in the low temperature range between 40degrees and 90 degreesC. In contrast, there is no significant difference obtained in friction coefficient between the presence and absence of soot in other CD and CG-4 oils. Distribution of soot particle sizes was measured with the DLS (Dynamic Light Scattering) technique to examine the correlation between lower frictional characteristics and fraction of soot particle sizes less than the estimated oil film thickness. Soot aggregates dispersed in the oils were also observed with the TEM-FFR (Freeze Fracture Replica) technique to investigate the impact of the actual state of soot in oils on frictional behavior.