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Pure biodiesel fuel (B100) is typically made of fatty acid methyl esters (FAME). FAME has different physical properties as compared to mineral diesel such as higher surface tension, lower volatility and higher specific gravity. These differences lead to a larger droplet size and thus more wall impingement of the fuel during injection in the combustion chamber. This results in higher levels of fuel dilution as the oil is scraped down into the crankcase by the scraper ring. The lower volatility also makes biodiesel more difficult to evaporate once it enters the crankcase. For these reasons, levels of fuel dilution in biodiesel fueled engines are likely to be higher compared to mineral diesel fueled engines. When in-cylinder dosing is applied to raise the exhaust temperature required for the regeneration of Diesel Particulate Filters (DPF's), biodiesel dilution in the engine oil may be elevated to high levels.

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.