The rising global energy demand, climate change considerations, and worldwide mandates to replace conventional energy supplies with renewable resources continue to drive increased use of biodiesel into the automotive market. OEM's have observed that usage of biodiesel fuel blends can lead to more fuel dilution of engine oil and as a consequence performance issues. The issue is more pronounced in modern, low emissions diesel engines equipped with Diesel Particulate Filters (DPF) in combination with late post-injection of fuel into the cylinders.
A prerequisite for the safe use of biodiesel is the availability of a cost effective detection method that allows an accurate measurement of the level of fuel dilution in used engine oil. It contributes to a better fundamental understanding of cause-effect relationships between biodiesel fuel dilution and engine lubricant performance. Due to chemical differences between biodiesel and mineral diesel, biodiesel has a higher and narrower boiling range leading to accumulation in the crankcase oil. Detection and quantification of biodiesel requires a different approach as compared to the analysis of mineral diesel in used engine oils.
In this paper a new approach for utilizing Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography Flame Ionized Detector (GC-FID) is introduced. The biodiesel and mineral diesel fuel dilution were measured in several engine oils. A method was developed for biodiesel analysis using a diverse set of used diesel crankcase oils. These oils, exhibiting a variety of parameters like low- and high soot contents, low- and high oxidization levels, different base oil groups, and different biodiesel fuel feed stocks, were obtained from field tests, laboratory engine tests, and laboratory preparation. Biodiesel fuel dilution levels < 5 wt % were measured in used oils samples obtained from engine tests and heavy-duty field tests that were not equipped with DPF. Levels of up to 25 wt % fuel dilution (10 wt % biodiesel and 15 wt % mineral diesel) were measured in a low emissions diesel engine field test, which used active regeneration of DPF and lean NOx trap.