Engine oil condition sensor: method for establishing correlation with total acid number

The engine oil condition sensor, invented at Delphi Automotive Systems, has the capability of detecting three oil degradation stages: good, rapid total acid number (TAN) increase, and rapid viscosity increase. During the second stage, the sensor output is expected to increase proportionally with TAN. In earlier experiments, the sensor output was compared to TAN obtained by a widely accepted titration method. The results suggested that the correlation between TAN and the sensor output could be improved if data scatter originated from the titration method is reduced. Therefore, a complementary method for determining TAN with less data scatter is highly desirable. In this report, the original assessment is confirmed by measuring TAN through both the titration and the electrochemical (EC) methods. The experimental results indicated that the TAN measured by the EC method could be complementary to that measured by the titration method. A good correlation was thus, established between the TAN and the sensor output obtained during the second oil degradation stage.