Development of advanced cylinder liner conformation concepts of internal combustion engines with numerical simulation methods

Internal combustion engine (ICE) represents the main pillar of the powertrain in the majority of road, marine freight, and transportation worldwide. With the absence of a real alternative that can replace ICE over its full range of applications, enhancing the efficiency of ICE is of great interest to save energy and reduce greenhouse gas emissions. A great improvement potential is seen in the piston ring – cylinder liner (PRCL) coupling which is responsible to maintain the combustion pressure in the cylinder while preventing lubricant oil leak to it. Large frictional losses are associated with this sealing function. In order to improve the PRCL conformability with less friction, a rounder liner cross section is targeted in the hot operational state. The rounder the liner is, the better conformability exists. To achieve that, the engine must be started with a non-circular liner that deforms in a controlled manner under engine thermal and mechanical loads to form a circular liner bore during the fire operation. Further tribological improvement can be achieved by targeting a non-prismatic circular bore shape in the hot operational state. This cumulative thesis presents numerical investigations to this reverse engineering approach with the aim to reach a specific liner shape in the fire operation state from non-cylindrically produced liners in the cold state. It follows the relevant research hypothesis and provides quantitative analysis to show the advantages and limitations of such an approach. The presented numerical work is based on advanced simulation techniques established on the basis of finite element methods. Two physical models were considered; one for a series gasoline engine, and the second for a single cylinder diesel engine test rig. The models were validated using experimental data, then the local deformations of the liners were simulated. Harmonic analysis was used to investigate the orders of deformations and their trends over a set of operational points. Then different forms of non-circular liners were designed based on the reverse engineering concept. Geometrical performance indicators were developed and used in the comparative analysis. The results show a significant improvement in the geometrical performance when using non-circular liners. Special freeform liner can improve the bore roundness by 95% and the straightness by 75%. The concept of dominant deformation order can simplify the design significantly. For example, the elliptical conus liner is a good yet simpler alternative with 85% improvement in roundness and 65% in the straightness of the liner during fire operation. The freeform liner is susceptible to the engine load. However, some deformation orders are independent of operational points and can be considered in the liner design. The results presented here show a great potential of tribological improvement. A parallel experimental work shows a significant reduction of frictional losses by using one of the liners that was designed in this thesis.