The assessment of surface acoustic wave sensing for testing fuel dilution of lubricating oils

This article presents an assessment of the accuracy and repeatability of oil dilution measuring apparatus. The device uses surface acoustic wave sensing (SAW), and the measurement method meets the ASTM D8004 standard. Since the described in the ASTM standard definitions of accuracy and repeatability are not easy to compare with definitions in the ISO standards, a comparative experiment was settled. Mixtures of the SAE 30 and SAE 40 grades lubricating oil with diesel oil in a high-precision concentration of 0, 1, 2, 5, and 10 % m/m were tested. The calculated root mean square error (RMSE) of measurement results against the expected value, was RMSESAE 30 = 0.57 % m/m and RMSESAE 40 = 1.33 % m/m. Additionally, the method based on the flash point was tested to compare estimated dilutions (SAW vs. flashpoint). The results show that the flash point gives a better estimation than SAW. The device can be used for industrial tests.