Markus Söderfjäll

Published: 26 January 2015

Simulation of twin land oil control ring in heavy duty diesel engines

With today’s striving towards reduction of fuel consumption it is more important than ever to understand how different components in the internal combustion engine function. There is a need for tools that can be used to investigate and predict the result of specific design changes made on the components. In this work, the mechanics and the tribology of the power cylinder unit and more specifically the operation of the twin land oil control ring (TLOCR) is investigated. In heavy duty diesel engines (HDDE), TLOCR are typically used. The TLOCR plays a very important role in the engine since it is supposed to distribute the correct amount of oil on the liner to lubricate the other rings. It is important that the TLOCR does not leave too much oil on the liner for the two top rings since it could lead too high oil consumption. In a HDDE the piston assembly is the largest contributor to frictional losses where the piston ring pack accounts for the major part of this. The oil control ring has the largest contribution to frictional losses in the piston ring pack therefore making it very interesting to study from a fuel consumption perspective. The objective of this thesis is to develop a simulation tool that can be used to quantify design changes to the TLOCR. Such as the dimensions of the ring itself but also ring tension, running land profile and out of roundness of the cylinder liner.

The model developed in this work accounts for the tribological interfaceof the TLOCR against the cylinder liner and  piston ring groove as well as the elastic deformation of the ring and the ring dynamics within the piston ring groove. The actual ring cross section is modelled in order to account for the full three dimensional elastic deformation of the ring. By solving all of these problems as a coupled system it is believed that the entire operation of the oil control ring could be understood in a better way than earlier and open up new optimisation possibilities for the TLOCR. The full ring is modelled in order to account for out of round cylinder liners. Since the cylinder liner in an engine will always have some deviation from perfectly round this is important. The model can therefore be used to investigate the effect on oil distribution by reduced ring tension which will affect the frictional losses of the system.