Influences of Lubricant Viscosity and Metallic Content on Diesel Soot Oxidation Reactivity

<div class="section abstract"><div class="htmlview paragraph">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.</div></div>