SATUFER Method for Determining the Degree of Lubricating Oil Dilution with Diesel Oil in an Internal Combustion Engine Lubrication System

This article presents a proposed a new method for estimating the degree of dilution of lubricating oil with diesel oil, which can be applied to systems for ongoing monitoring of lubricating oil quality in an internal combustion engine. The test is performed for reference blends based on two commonly used single-season lubricating oils for marine and industrial engines. SAE 30 and SAE 40 viscosity grade base oils and ISO-F-DMX category diesel oil are used. For each base oil, reference blends are prepared with diesel oil content in the lubricating oil mixture equal to 0, 1, 2, 5, 10, 20, 30, 40, 50, 75, and 100% m/m. Concentration estimates are made for each mixture based on measured kinematic viscosity at different temperatures. Measurements are made for 40, 50, 60, 70, 80, 90, and 100 °C. The results are evaluated by determining the model’s fit to the empirical data and the maximum percentage absolute error in estimating the degree of dilution of the lubricating oil with diesel fuel. The results are contrasted with a previously used model based on the inverse Arrhenius equation for determining the viscosity of binary mixtures. The proposed new model for both base oils, for all tested reference concentrations and for all tested temperatures shows a much better fit to empirical data (R2 > 0.999). Moreover, the maximum absolute error of the SATUFER estimation did not exceed the value of 1.5% m/m and, relative to the model based on the inverse Arrhenius equation, it is ~8.9 times higher for mixtures of SAE 30 grade base oil and ~10.3 for mixtures of SAE 40 grade base oil.