Oljetemperaturens inverkan på motoroljans degradering i lastbil

Sammanfattning: The market for heavy duty engines is constantly requiring engines that should be more and more powerful, while still maintaining low fuel consumption. As a result of increasing engine power, the engine and coolant temperature increases as well due to insufficient cooling performance (because of design issues, cost etc.). Also, emission legislations, both current and future, require more and more measures to be taken 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 consequences of 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 have been performed on a 310 hp engine with EGR to see what happens to the engine oil in a real engine when exposed to high temperatures. During the tests oil samples have been taken and analysed for important parameters. As a complement to these engine tests some laboratory oxidation testing have also been performed, 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 be able to predict oil oxidation levels in an engine, given any running parameters. This model was to be based on the results of the engine tests and oil analysis. This goal was not achieved though, as it showed that the engine tests were too short to show any good tendencies in oil oxidation. It was therefore decided that further and longer engine tests were to be made, but these did not fit into the timeframe of this project. However, an embryo of an oxidation model has 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 high temperatures in an engine, and to discuss what can be done to improve the situation. Whether or not a dedicated oil temperature gauge in production engines is needed, and where that would be mounted, is discussed. This has been done based on the results of the engine and laboratory testing. One interesting finding is that increasing the flow to the piston cooling system does not seem to improve anything for the oil; instead the oil consumption as well as oil oxidation seems to be able to increase. Another conclusion is that using a sump oil temperature gauge as a standard part of the new engine generation might be a good idea, since it has been shown that high engine oil temperatures in the sump have great negative effects on engine oil oxidation, and that the oil temperature in the sump is behaving quite irregularly in relation to other oil temperatures. To support the work in this project a thorough literature survey was undertaken including various SAE and other technical papers, books and Scania reports. Based on these facts the procedures behind engine oil oxidation on a chemical level have been investigated, among other things. For confidentiality reasons this report has been edited in such a way that absolute values of measured parameters have been removed. Where possible, these values have been replaced by percentages of normal values.