Thermogravimetric analysis of carbon black and engine soot—Towards a more robust oil analysis method

This work examined the thermal behaviour of diesel engine produced soot and commercial carbon black using thermogravimetric analysis (TGA). It was found that during TGA analysis of the carbon matrices (at a temperature range commonly used for soot-in-oil content determination), a gradual mass loss occurred. This was attributed to pyrolysis effects and combustion processes occurring due to poor hydrodynamic design of some commercial thermobalances. This process resulted in a significant mass loss of the carbon during TGA. This finding may strongly effect soot-in-oil analysis conducted using current methods. Experiments were conducted using a range of soot-in-oil mixtures according to the widely used thermogravimetric standard method ASTM 5967-08 which showed a significant underestimation of the soot content in the oil as a result of carbon mass loss due to combustion and/or pyrolysis effects. An improved oil analysis method is proposed which provides a significantly increased accuracy of soot determination in lubricant oils.

► Hydrodynamic properties of TGA instruments can prevent a complete oxygen evacuation.
► Remaining oxygen in TGA can lead to soot combustion in oil analysis.
► Cu-II-Oxalate test allows the detection of remaining oxygen in the TGA instrument.
► Combustion/pyrolysis affects results of existing ASTM oil analysis method.
► Modified method more robust against combustion/pyrolysis.