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.