Influence of Different Biogenic Fuels on Base Oil Aging 2014-01-2788

Increasing the proportion of renewable energy in the transport sector and therefore the reduction of the dependence on fossil oil is a prime political and economic goal in Europe and also in many other parts of the world. In the diesel sector, especially vegetable oil methyl ester is introduced. The blending of commercial diesel fuel with up to 7 % of biodiesel leads to a lot of problems in the range of engine oil in cars. Because of the regeneration of diesel particle filter, there is an increase entry of unburnt fuel into the engine oil. The first effect of this fuel entry is the engine oil dilution which can be observed for all diesel fuels. Unlike biodiesel, commercial diesel fuel can mostly evaporate out of the engine oil because of its boiling range between 165 °C and 360 °C (73 % of the fuel has a boiling point under 320 °C). The boiling range of fossil diesel fuel was measured in preparation of this study. Biodiesel has a boiling point of about 360 °C which is the reason for its accumulation in the engine oil. High temperatures and atmospheric oxygen have a big influence on the oil and thus also on the fuel in engines. The underlying effect is an autoxidation reaction which is known as oil aging. Additionally to the engine oil dilution, the autoxidation of the oil and the biodiesel leads to an aging process which forms oligomer structures. Additives like antioxidants can affect this aging process in the engine.

This work describes aging oil studies in the laboratory on neat base oil with different biogenic fuel. Neat base oil was used to prevent the influence of the additives. Besides the regional biodiesel, which consists of rapeseed oil, other vegetable oil methyl esters, which are used as biodiesel in other parts of the world as well as hydrotreated vegetable oil (HVO), were also used in a mixture with neat base oil. In the aging studies, neat base oil was blended with 20 % biogenic fuel to simulate the worst case of oil sludge formation. It could be observed that on the basis of the different biogenic fuels the aging of the neat base oil mixture was influenced. The reason for this impact is the variety in the chemical structure of the used biogenic fuels. For example the influence of biodiesel to the aging process is inferior to HVO because of the ester group and the double bond of biodiesel.

In this study, the influence of rapseed oil methyl ester (RME), coconut oil methyl ester (CME) and linseed oil methyl ester (LME) as well as a new biogenic fuel called Diesel regenerativ on oligomer and oil sludge formation in neat base oil was examined.