This study examined the effects of lubricant viscosity and metallic content on
the oxidation reactivity of diesel particles. In the first part, the factors
affecting thermogravimetric analysis (TGA) experiments was discussed and
confirmed. The influences of initial soot mass, heating rate, and airflow rate
on soot oxidation rate and experimental reproducibility were investigated to
develop an optimized TGA method. On the basis of these experiments, an initial
soot mass of 2.0 mg, airflow rate of 4.8 L/h, and heating rate of 2.5°C/h were
used for all subsequent TGA tests. It could be found that the TGA experiments
had high repeatability, and the differences were less than 0.1%. In the second
part, a four-cylinder diesel engine was lubricated with seven kinds of lubricant
with different viscosity and metallic content by the use of viscosity index
improver (VII), antioxidant and corrosion inhibitor (ACI), and ashless
dispersant (AD). Particle samples were subjected to TGA to test their
particulate composition and oxidation reactivity, such as oxidation rate,
characteristic temperatures, and Arrhenius kinetic parameters. It was found that
the soot oxidation rate increased significantly with the increase of metallic
content in lubricant, but had little to do with lubricant viscosity. When using
lubricating oils with different properties and compositions, the activation
energy of carbon smoke oxidation ranges from 143 to 187 kJ/mol. This tendency
was more remarked as the lubricant additives’ dosage ratio increased. Soot
oxidation rate trends were explained by particle properties, including
morphology and nanostructure. A smaller size and less ordered nanostructure were
associated with a lower activation energy.