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High concentrations of diesel fuel can accumulate in the engine oil, especially in vehicles equipped with diesel particle filters. Fuel dilution can decrease the viscosity of engine oil, reducing its film thickness. Higher concentrations of fuel are believed to accumulate in oil with biodiesel than with diesel fuel because biodiesel has a higher boiling temperature range, allowing it to persist in the sump. Numerous countries are taking actions to promote the use of biodiesel. The growing interest for biodiesel has been driven by a desire for energy independence (domestically produced), the increasing cost of petroleum-derived fuels, and an interest in reducing greenhouse gas emissions. Biodiesel can affect engine lubrication (through fuel dilution), as its physical and chemical properties are significantly different from those of petrodiesel. Many risks associated with excessive biodiesel dilution have been identified, yet its actual impact has not been well quantified.

Valvetrain friction can represent a substantial portion of overall engine friction, especially at low operating speed. This paper describes the methodology for predictive modeling of frictional losses in the direct-acting mechanical bucket tappet-type valvetrain. The proposed modeling technique combines advanced mathematical models based on established theories of Hertzian contact, hydrodynamic and elastohydrodynamic lubrication (EHL), asperity contact of rough surfaces, flash temperature, and lubricant rheology with detailed measurements of lubricant properties and surface finish, driven by a detailed analysis of valvetrain system kinematics and dynamics. The contributions of individual friction components to the overall valvetrain frictional loss were identified and quantified. Calculated valvetrain friction was validated against motored valvetrain friction torque measurements on two engines.