A study was undertaken to investigate the affect of exhaust gas recirculation (EGR) on engine wear and lubricating oil degradation in a heavy duty diesel engine using a newly developed methodology that uses analytical ferrography in conjunction with short term tests. Laboratory engine testing was carried out on a Cummins NTC-300 Big Cam II diesel engine at rated speed (1800 RPM) and 75% rated load with EGR rates of 0, 5, and 15% using a SAE 15W40 CD/SF/EO-K oil. Dynamometer engine testing involved collecting oil samples from the engine sump at specified time intervals through each engine test. These oil samples were analyzed using a number of different oil analysis techniques that provide information on the metal wear debris and also on the lubricating oil properties. The results from these oil analysis techniques are the basis of determining the effect of EGR on engine wear and lubricating oil degradation, rather than an actual engine tear down between engine tests.
The principal oil analysis technique used was analytical ferrography, which is a sensitive wear measurement technique that provides good qualitative and quantitative capabilities for the metal wear debris. The qualitative aspect of analytical ferrography can provide information on the wear particle size distribution, morphology, and mode of wear. Quantitative ferrographic data can be used in conjunction with a mathematical model that describes the wear particle concentration build-up to determine two important wear parameters, the wear particle generation rate and filter efficiency. Additional oil analysis data were taken to provide information on the viscosity, soot loading, level of insolubles, and elemental analysis of the wear elements and oil additives.
Engine testing was divided into three main sequences: baseline engine testing, EGR engine testing, and EGR/baseline engine testing combined. All the engine tests were approximately 5 to 6 hours in length and each started with a low initial wear particle concentration. An external oil circuit was set-up in conjunction with a high gradient magnetic separator (HGMS) to achieve this low initial wear particle concentration. The initial baseline engine testing sequence was done to establish a data base of normal engine wear prior to engine testing with EGR. The second engine test sequence involved a series of engine tests with 5% EGR and the third engine test sequence involved three 5% EGR tests followed by two baseline engine tests and then a final series of engine tests with 15% EGR.
The results from the baseline engine testing sequence indicate this particular engine/oil combination produces an extremely low wear rate, resulting in a very low equilibrium particle concentration. Additional oil analysis results showed that no significant changes to lubricating oil properties had occurred over these relatively short engine tests. Results from the final engine testing sequence with EGR suggest that EGR may cause a faster wear particle concentration build-up, although the equilibrium particle concentration remained essentially unchanged from the baseline engine testing sequence. Engine testing with 15% EGR showed a significant increase in the wear particle generation rate and the equilibrium particle concentration from the baseline engine testing results. The equilibrium particle concentration with 15% EGR was approximately 10 times higher than baseline engine testing. The study showed the applicability of the overall methodology of using ferrography in conjunction with the test set-up and other oil analysis methods for the study of lubrication system or engine variables.