Investigating the morphology and nanostructure of carbon black dispersed in lubricant oils and their impact on chain wear as a proxy of marginally lubricated components

Excessive soot concentration in the lubricant promotes excessive wear on timing chains. The relationship between chain wear and soot concentration, morphology, and nanostructure, however, remains inconclusive. In this work, a chain wear test rig is used to motor a 1.3 L diesel engine following the speed profile of a Worldwide Harmonized Light Vehicle Test Cycle (WLTC). The lubricant oil was loaded with 3% carbon black of known morphology. The chain length is measured at regular intervals of 20 WLTC cycles (i.e. 10 hours) and the wear is expressed as a percentage of total elongation. Oil samples were collected and analysed with the same frequency as the chain measurements. Carbon black morphology and nanostructure were investigated using Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). DLS data revealed carbon black particle size did not change substantially in the first 10 hours, however, during the remaining test cycles a reduction in agglomerates size over time was observed. The wear results show that adding carbon black to the lubricating oil promotes chain elongation by up to 0.10%. Significant chain elongation occurred within the first 10 hours (+0.06%), with further increase in elongation occurring in the remaining 40 hours (+0.04%) but under a reduced wear rate. The overall results suggest that dynamically changing carbon black size distributions and nanostructure could be linked changes over time.