On-Board Sensor Systems to Diagnose Condition of Diesel Engine Lubricants - Focus on Soot

Soot is a typical byproduct of the diesel fuel combustion process, and a portion of the soot inevitably enters an engine's crankcase. A key functionality of a diesel engine lubricant is to disperse and suspend soot so that larger-particle agglomerations are prevented. The role of soot agglomeration in abrasive engine wear and lubricant viscosity increase is the subject of a continuing investigation; however, what is generally known is that once an engine lubricant loses its ability to control soot and a rapid viscosity increase begins, the lubricant has reached the end of its useful life and should be changed to maximize engine performance and life. This issue of soot related viscosity increase is of such importance that the Mack T-11 engine test was developed as a laboratory tool to evaluate lubricants. The newly proposed Mack EO-N Premium Plus - 03 specification includes a T-11 performance requirement. Recently, a study was run using a variety of lubricants to compare the T-11 test to a carefully controlled field test. The results of that study are the subject of a separate paper. In conjunction with the field work, on-board sensor systems were installed on the test vehicle's engine. The sensor systems included hardware and software being developed to measure and diagnose/predict the condition of the lubricant in real-time, i.e., as the engine operates.

This paper focuses on the successful application of electrochemical sensor technology to diagnose soot content and soot related viscosity increase as typically measured by standard laboratory lubricant analysis. Other on-board sensor technologies used in the field test are briefly reviewed. The need for multiple sensing strategies to completely diagnose modern lubricants with their complex decomposition pathways is discussed.