Design of piston rings is a very crucial subject in the field of internal combustion engines. In the present paper, a numerical model is created using the Navier–Stokes equations. Fluid–structure interaction analysis is performed in order to calculate the structural integrity of the ring for several engine operational conditions and texturing patterns. This paper illustrates the hydrodynamic friction force under various surface artificial texturing in terms of spherical and rectangular microdimples. Piston ring stress analysis is also investigated due to gas leakage. Results show a substantial reduction of the friction using rectangular texturing and less reduction using spherical texturing. The rectangular microdimple parameters were considered to obtain a better friction reduction with the following configurations: Hd = 4 µm, ρτ = 0.61, λ = 20 and s = 0.004. Each rectangular texture cell is defined by the dimple depth, Hd; the texture density, ρτ; the dimple aspect ratio, λ; and the relative dimple depth, s. Copyright © 2014 John Wiley & Sons, Ltd.

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A 2D axisymmetric hydrodynamic model was developed considering fluid structure interaction analysis in order to solve the Navier–Stokes equations. The effect of lubricants viscosities in terms of both monograde and multigrade oils, on the produced piston ring friction force are compared, using smooth and textured piston rings. The novelty of the current paper is the solution of the Navier–Stokes equations with the use of power law lubricants, which act in non-Newtonian shear for the piston ring friction problem. The lubricant viscosity variation in relation to the temperature has been taken into account. Simulation shows a good prediction at lower loads and higher piston speeds. The hydrodynamic pressure, the oil film thickness and the friction force on smooth and textured flat piston ring are predicted and presented.

To further improve efficiency in automotive engine systems, it is important to understand the generation of friction in its components. Accurate simulation and modeling of friction in machine components is, amongst other things, dependent on realistic lubricant rheology and lubricant properties, where especially the latter may change as the machine ages. Some results of research under laboratory conditions on the aging of engine commercial oils with different performance levels (mineral SAE 30, synthetic SAE10W-40, and bio-based) are presented in this paper. The key role of the action of pressure and temperature in engine oils’ aging is described. The paper includes the results of experiments over time in laboratory testing of a single cylinder motorbike. The aging of engine oil causes changes to its dynamic viscosity value. The aim of this work is to evaluate changes due to temperature and pressure in viscosity of engine oil over its lifetime and to perform uncertainty analysis of the measured values. The results are presented as the characteristics of viscosity and time in various temperatures and the shear rates/pressures. This paper also includes a Computational Fluid Dynamics (CFD) model, applying the experimental results in the piston ring tribology problem.

Purpose Compression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top compression rings. To understand the coating effects, the main tribological parameters are investigated into a ring-cylinder conjunction in a motorbike engine. Furthermore, flow simulations have been carried out on how different worn profiles on the cylinder inner liner affects friction, lubricant film and localized contact deformation of the coated compression rings. Design/methodology/approach In this paper, the basic geometrical dimensions of the top compression ring-cylinder system are obtained from a real motorbike engine. A 2D axisymmetric CFD/FLOTRAN model is created for coated compression rings. Flow simulations are performed by solving the Navier-Stokes and the energy equations. The load capacity of the asperities is also taken into account by Greenwood and Tripp contact model. Realistic boundary conditions are imposed to simulate the in-plane ring motion. The simulation model is validated with analytical and experimental data from the literature. Under thermal considerations, the contribution of worn cylinder profiles in conjunction with different coated compression rings is presented. Findings This research shows that because of thermal effects, the boundary friction is higher at reversals and the viscous friction is lower because of reduced oil viscosity. As regards to the isothermal case, the viscous friction is greater because of a higher lubricant viscosity. In the case of chromium-plated ring, boundary friction was 16 per cent lower than a grey cast iron ring taking into account thermal effects. Regarding the localized contact deformation, the coated compression rings showed lower values under different worn cylinder shapes. In particular, hard wear-resistant (Ni-Cr-Mo) coating showed the slighter local deformation. Therefore, the worn cylinder profiles promote boundary/mixed lubrication regime, whereas the lobed profile of cylinder inner liner becomes more wavy. Originality/value The solution of the thermo-mixed lubrication model, concerning the piston ring and worn cylinder tribo pair by taking into account the coating of the top compression ring.