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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.

Ethanol is widely used as a gasoline component to provide a prescribed amount of oxygenates and for its perceived advantages of less dependence on petroleum based products and lowering overall CO2 emissions. In most cases the level of ethanol in gasoline does not exceed 10%. In some parts of the Unites States, E85 fuel consisting of 85% ethanol and 15% gasoline is commonly available. Many US vehicles sold today are specially adapted for use of both gasoline and high ethanol fuels; so-called Flexible Fuel Vehicles (FFV). While high ethanol fuels are currently a small percentage of the overall gasoline pool, they provide an interesting opportunity to study the effects that ethanol use in gasoline may have on lubricant related performance. Based on past industry experience with methanol based fuel, theoretical areas of concern for ethanol based fuels are valve train rust and potential problems associated with high amounts of water in the lubricant.

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.