Impact of pure biodiesel fuel on the service life of engine-lubricant: A case study

This work presents a study about the effects that pure biodiesel fuel causes on the engine-lubricant oil. For this study a fleet of buses employed for urban public transportation in the city of Curitiba, Southern Brazil, was monitored along 18 months. Samples of engine lubricant were collected periodically from a set of 7 vehicles, 4 of which ran fueled by pure biodiesel, while the other 3 utilized mineral diesel fuel, thus the latter group served as a reference for comparisons. The collected samples had the following characteristics evaluated: viscosity, basicity, acidity, oxidation, as well as content of iron, copper, lead and aluminum. The analysis of gathered data allowed pointing out the viscosity as the most sensitive among the characteristics of the engine-lubricant oil that are affected by the use of pure biodiesel fuel, thus enabling its adoption as a control parameter for judging whether the lubricant charge is still serviceable. In addition, it was found that replacing mineral diesel by pure biodiesel fuel diminished the service-life mileage of the engine-lubricant oil charge from 20,000 to 13,000 km for mono-articulated buses, and from 15,000 to 10,000 km for bi-articulated ones. Therefore, this mileage was reduced to approximately two-thirds of the value recommended for vehicles fueled by conventional diesel.