Evaluation of lubricating oil in marine diesel engine using thermal analysis, FTIR, and rheology

Analysis of used lubricating oils is one of the tools that enable the diagnosis of the operation condition of the engine, and it is a widespread predictive maintenance practice in the marine sector. This study aimed to evaluate by thermal analysis, FTIR and rheology, lubricating oils before and after use in diesel marine engine and their additives, to monitor the physical integrity of these materials by evaluating their physical and chemical stability. Samples with 5280 and 8242 h of use showed thermal degradation profiles similar to unused lubricant oil on the TG curves. In contrast, a one with 7498 h of use presented higher thermal stability than the new lubricant, with only one stage of decomposition from 225 to 400 degrees C, indicating that their additives were probably no longer present in their original structure. That was confirmed by the FTIR spectrum of this sample, which showed scarce absorption bands of additives at their characteristic wavenumbers and distinctive bands of carbonyl groups indicating oil oxidation. This same sample also presented the lowest viscosity values on rheological tests, confirming the depletion of additives. On the other hand, the characterization techniques showed that the sample with 8242 h of use, with more hours of operation, maintained its physical-chemical integrity compared to unused lubricating oil.

Automated summary

This study evaluated the physical and chemical stability of lubricating oils and their additives before and after use in a diesel marine engine through thermal analysis, FTIR, and rheology. The results showed that samples with shorter usage time had greater performance degradation and depletion of additives, while samples with longer usage time maintained better physical-chemical integrity.