TriboUK 2015 Loughborough University, April 16 – 17th, 2015
Tribology of Piston Rings: From the Design to Applications Anastasios Zavos* and Pantelis G. Nikolakopoulos, (* indicating the Presenter) Machine Design Laboratory, Mechanical Engineering and Aeronautics Department, University of Patras *Corresponding author:
[email protected]
Piston rings are the most complicated component of the internal combustion engine. They are designed to seal the combustion chamber of the engine while minimizing the friction against the cylinder liner. Modern automobiles normally use three rings: two compressions rings and one oil ring. The first compression ring is the closest to the combustion chamber, so that it is exposed to the extreme conditions and rapidly changing loads associated with the combustion itself. Designs have been developed to improve ring friction and load carrying capacity by applying artificial surface texturing. Wear and lubrication also play a significant role in the life and performance of a ring.
results near to the power and the compression strokes have a large difference of 20-30% between the results.
1. Introduction The piston ring lubrication conditions and wear effects have been investigated analytically using the average Reynolds and Navier Stokes equations [1-3]. Textured piston rings have been found to reduce the friction and improve the oil film distribution in hydrodynamic lubrication [4]. 2. Methodology/Results/Discussion The geometry of the piston ring pack and cylinder were obtained for a four stroke, 107 cc, motor engine located at the Machine Design Laboratory of the University of Patras. The motor engine is lubricated by SAE 30 oil. Figure 1 shows the temperature distribution for the engine under operation conditions, using a high performance thermo-camera, FLIR type. The engine is arranged on a stiff steel base and cooled in a controlled manner by an air-condition system.
Figure 2. (a) Comparison of numerical and experimental friction results for SAE 30, (b) Strain gauge position.
Scanning Electron Microscope (SEM) analysis of a worn top ring was also obtained for 4000 operating hours, from a 2-stroke, 50 cc engine. Large width wear scars (Figure 3) were observed in the sliding direction (~8 μm) demonstrating the harsh conditions experienced by the piston rings and the need for careful design.
Figure 3. SEM image of worn top ring
3. References [1]
[2]
Figure 1. Temperature field along to cylinder liner for 1500 rpm
Computational Fluid Dynamics (CFD) numerical friction results were compared with the experimental results obtained from the engine and are presented in Figure 2(a). The experimental friction results were measured using the strain gauge method (see Figure 2(b)). The deviations of predicted and measured friction vary by 7-15% in the intake and exhaust stages. The
[3]
[4]
Morris, N., Rahmani, R., Rahnejat, H., King, PD., and Fitzsimons, B., "The influence of piston ring geometry and topography on friction," Part J: Jou. of Eng. Trib. vol. 227, pp. 141-153, 2013. Zavos, A. and Nikolakopoulos, PG., "Effects of Monograde and Multigrade Oils on the Friction Force in Four-Stroke Motor Engine: An Experimental and Analytical Approach", In book: Vibration Engineering and Technology of Machinery, Vol. 23, pp. 507-517, 2015. Zavos, A. and Nikolakopoulos, PG., "Friction Force Prediction on Piston rings under Surface irregularities and Oil Viscosity Effects,in:Proc. of BALKANTRIB'14. Ryk, G., and Etsion, I., "Testing piston rings with partial laser surface texturing for friction reduction," Wear, vol. 261, pp. 792-796, 2006.
