Oljetemperaturens inverkan på motoroljans degradering i lastbil
The market for heavy duty engines is constantly requiring engines that should be more andmore powerful, while still maintaining low fuel consumption. As a result of increasing enginepower, the engine and coolant temperature increases as well due to insufficient coolingperformance (because of design issues, cost etc.).Also, emission legislations, both current and future, require more and more measures to betaken by engine manufacturers. One way of meeting the legislations is the use of cooled EGR(Exhaust Gas Recirculation), which also lead to increased coolant temperatures.Both these factors also naturally lead to increased engine oil temperatures, the consequencesof which are not thoroughly investigated.This thesis project aims to investigate effects of high temperatures on engine oil degradation,with focus on the greatest degradation process: oxidation. To do this several engine runs havebeen performed on a 310 hp engine with EGR to see what happens to the engine oil in a realengine when exposed to high temperatures. During the tests oil samples have been taken andanalysed for important parameters.As a complement to these engine tests some laboratory oxidation testing have also beenperformed, to be able to compare engine test data with laboratory tests.One goal of the project was to try to formulate an empirical oxidation model, which would beable to predict oil oxidation levels in an engine, given any running parameters. This modelwas to be based on the results of the engine tests and oil analysis. This goal was not achievedthough, as it showed that the engine tests were too short to show any good tendencies in oiloxidation. It was therefore decided that further and longer engine tests were to be made, butthese did not fit into the timeframe of this project. However, an embryo of an oxidation modelhas been presented, and suggestions for further development have been made.Another goal was to clarify where and to what extent the engine oil is exposed to hightemperatures in an engine, and to discuss what can be done to improve the situation. Whetheror not a dedicated oil temperature gauge in production engines is needed, and where thatwould be mounted, is discussed. This has been done based on the results of the engine andlaboratory testing. One interesting finding is that increasing the flow to the piston coolingsystem does not seem to improve anything for the oil; instead the oil consumption as well asoil oxidation seems to be able to increase. Another conclusion is that using a sump oiltemperature gauge as a standard part of the new engine generation might be a good idea, sinceit has been shown that high engine oil temperatures in the sump have great negative effects onengine oil oxidation, and that the oil temperature in the sump is behaving quite irregularly inrelation to other oil temperatures.To support the work in this project a thorough literature survey was undertaken includingvarious SAE and other technical papers, books and Scania reports. Based on these facts theprocedures behind engine oil oxidation on a chemical level have been investigated, amongother things.For confidentiality reasons this report has been edited in such a way that absolute values ofmeasured parameters have been removed. Where possible, these values have been replaced bypercentages of normal values.