Effects of Lubricant Viscosity on Ring/Liner Friction in Advanced Reciprocating Engine Systems

2006 ◽  
Author(s):  
Rosalind Takata ◽  
Victor W. Wong
Keyword(s):  
Shear Rate ◽  
Combustion Engine ◽  
Current Model ◽  
Friction Reduction ◽  
Asperity Contact ◽  
Oil Viscosity ◽  
Hydrodynamic Friction ◽  
Piston Speed ◽  
Ring Pack ◽  
Lubricant Viscosity

The piston ring-pack contributes a large portion of the mechanical losses in an internal combustion engine. In this study, the effects of lubricant viscosity are evaluated with the goal of reducing these mechanical losses. Oil viscosity affects friction directly in the hydrodynamic regime, where hydrodynamic friction increases with viscosity. It also influences boundary friction indirectly via oil film thickness — higher viscosity causes oil films to be thicker, which reduces asperity contact. At the optimum viscosity (the viscosity at which minimum friction losses are incurred) there is a balance between these hydrodynamic and boundary effects. As piston speed, ring loading, and other parameters change during the engine cycle, the optimum oil viscosity also changes. If the variation of viscosity could be controlled during the cycle, it could be maintained at an optimum at all times. In this study, several theoretical and realistic cases were studied to quantify the friction benefit that could be obtained if this were possible. Idealized cases with low viscosity near mid-stroke (to reduce hydrodynamic friction) and high viscosity near end-strokes (to reduce boundary contact) were considered, as were several more realistic cases based on temperature and shear-rate dependencies. It was found that, for the oil control ring studied, the effect on friction of keeping viscosity high near end-strokes is very small, and does not provide a substantial benefit (in terms of friction) over allowing viscosity to vary naturally with temperature and shear rate. Two mechanisms lead to the relatively small size of the friction benefit: the contribution to total cycle ring friction from the dead-center area is small, because of low piston speeds there; and any reduction in asperity contact due to increased viscosity is accompanied by an increase in hydrodynamic friction, which cancels out some of the benefit. Oil viscosity near mid-stroke, where most of the ring/liner friction is generated, is the dominant viscosity that controls the overall friction losses for the ring. Although its contribution to friction reduction is not large, maintaining high lubricant viscosity near dead-centers can lead to a reduction in wear in that region, because asperity contact decreases. For the ring-pack studied, a friction reduction of ∼7% is predicted when viscosity is reduced in the mid-stroke region (based on OCR effects alone). If end-stroke viscosity is also kept high, the end-stroke regions, where current engines experience the most wear, will see a reduction in asperity contact (although there will still be a slight wear increase in the mid-stroke). An end-stroke wear reduction of up to 25% is predicted by the current model.

Viscosity in Exploitation Time Analysis of the Lubricating Oil Used in the Combustion Engine of the Personal Car

2015 ◽  
Vol 220-221 ◽  
pp. 271-276 ◽  
Author(s):  
Grzegorz Sikora ◽  
Andrzej Miszczak
Keyword(s):  
Shear Rate ◽  
Dynamic Viscosity ◽  
Combustion Engine ◽  
High Shear Rate ◽  
Engine Oil ◽  
Lubricating Oil ◽  
High Shear ◽  
Oil Viscosity ◽  
Peltier Element ◽  
Engine Model

The aim of this study is to develop a mathematical model of the lubricating oil viscosity changes during the exploitation time of the engine.The aim was achieved by measurements of dynamic viscosity of engine oil used in a passenger car Volkswagen Touran equipped with a turbocharged diesel engine with a capacity of 2.0 liters. The recommended interval for oil change in this engine model is 30000 km. Oil used in this study was Shell Helix AV-L (viscosity grade SAE 5W30, designation VW: 50700).Viscosity tests were made on a Haake MARS III using two measuring systems. The first consisted of a plate-cone system with Peltier element for temperature stabilization. The second one is the high shear rate chamber with temperature control thermostat co-operating with ultra-A40 AC200 which can operate at temperatures ranging from-40 °C to +200 °C. The high shear rate chamber, consisting of a measuring cylinder and the rotor, the shear rate can achieve up to 200000 s–1.Dynamic viscosity measurements were performed at temperatures ranging from 20 °C to 90 °C.The results of the research are shown in the graphs and in tabular form. Obtained graphs made it possible to determine characteristics of the oil ageing for each mileages, temperatures and shear rates.

Analysis of Oil Film Thickness and Heat Transfer on a Piston Ring of a Diesel Engine: Effect of Lubricant Viscosity

2002 ◽  
Author(s):  
Yasuo Harigaya ◽  
Michiyoshi Suzuki ◽  
Fujio Toda ◽  
Masaaki Takiguchi
Keyword(s):  
Heat Transfer ◽  
Diesel Engine ◽  
Shear Rate ◽  
Film Thickness ◽  
Piston Ring ◽  
Unsteady State ◽  
Oil Viscosity ◽  
Oil Film ◽  
Higher Temperature ◽  
Lubricant Viscosity

The effect of lubricant viscosity on the temperature and thickness in oil film on a piston ring in a diesel engine was analyzed by using unsteady state thermohydrodynamic lubrication analysis, that is Reynolds equation and an unsteady state two-dimensional (2-D) energy equation with heat generated from viscous dissipation. The oil film viscosity was then estimated by using the mean oil film temperature and the shear rate for multi grade oils. The shear rate between the ring and liner becomes higher, so that the viscosity for the multi grade oil is affected by the oil film temperature and shear rate, and the viscosity becomes lower. Under low temperature condition, the viscosity becomes lower due to viscous heating and shear rate and under higher temperature condition, the viscosity affected by the shear rate becomes lower. The oil film thickness between the ring and liner decreases with decrease of the oil viscosity, and it is the thinnest that the oil film thickness is calculated by using the viscosity estimated by both the shear rate and the oil film temperature. Moreover, the heat transfer at ring and liner surfaces was examined.

Friction Reduction in Lubricated Rough Contacts: Numerical and Experimental Studies

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Zhiqiang Liu ◽  
Arup Gangopadhyay
Keyword(s):  
Friction Coefficient ◽  
Ambient Pressure ◽  
Classical Model ◽  
Experimental Studies ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Friction Reduction ◽  
Asperity Contact ◽  
Oil Viscosity ◽  
Lubrication Regimes

Combining the contact model of elastic-layered solid with the concept of asperity contact in elastohydrodynamic lubrication (EHL), a mixed-lubrication model is presented to predict friction coefficient over rough surfaces with/without an elastic-layered medium under entire lubrication regimes. Solution of contact problems for elastic-layered solids is presented based upon the classical model of Greenwood and Williamson (GW) in conjunction with Chen and Engel's analysis. The effects of the Young's modulus ratio of the layer to substrate and the thickness of the layer on the elastic real area of contact and contact load for a fixed dimensionless separation are studied using the proposed method, which is used for the asperities having contact with an elastic coating. Coefficient of friction with elastic-layered solids in boundary lubrication is calculated in terms of Rabinowicz's findings and elastic-layered solutions of Gupta and Walowit. The effect of rough contacts with an elastic layer on friction coefficient in lubrication regimes has been analyzed. Variations in plasticity index ψ significantly affect friction coefficients in boundary and mixed lubrications. For a large value of ψ, the degree of plastic contact exhibits a stronger dependence of the mean separation or film thickness than the roughness, and for a small value of ψ, the opposite result is true. The effect of governing parameters, such as inlet oil viscosity at ambient pressure, pressure–viscosity coefficient, combined surface roughness, and El/E2 on friction coefficient, has been investigated. Simulations are shown to be in good agreement with the experimental friction data.

Analysis of the Piston Ring/Liner Oil Film Development During Warm-Up for an SI-Engine

2000 ◽  
Vol 123 (1) ◽  
pp. 109-116 ◽  
Author(s):  
K. Froelund ◽  
J. Schramm ◽  
T. Tian ◽  
V. Wong ◽  
S. Hochgreb
Keyword(s):  
Piston Ring ◽  
Hydrodynamic Lubrication ◽  
Spark Ignition Engine ◽  
Asperity Contact ◽  
Oil Viscosity ◽  
Warm Up ◽  
Oil Film ◽  
Lubrication Regimes ◽  
Ring Pack ◽  
Film Development

A one-dimensional ring-pack lubrication model developed at MIT is applied to simulate the oil film behavior during the warm-up period of a Kohler spark ignition engine. This is done by making assumptions for the evolution of the oil temperatures during warm-up and that the oil control ring during downstrokes is fully flooded. The ring-pack lubrication model includes features such as three different lubrication regimes, i.e., pure hydrodynamic lubrication, boundary lubrication and pure asperity contact, nonsteady wetting of both inlet and outlet of the piston ring, capability to use all ring face profiles that can be approximated by piece-wise polynomials, and, finally, the ability to model the rheology of multigrade oils. Not surprisingly, the simulations show that by far the most important parameter is the temperature dependence of the oil viscosity.

Modeling of Axial and Circumferential Ring Pack Lubrication

2001 ◽  
Author(s):  
Mikhail A. Ejakov
Keyword(s):  
Hydrodynamic Lubrication ◽  
Three Dimensional ◽  
Cylinder Liner ◽  
Mixed Lubrication ◽  
Contact Boundary ◽  
Asperity Contact ◽  
Oil Viscosity ◽  
Friction Forces ◽  
Crank Angle ◽  
Ring Pack

Abstract The ring-pack lubrication is a complicated physical process involving multiple physical phenomena. This paper presents an attempt to model the ring-pack lubrication in three-dimensional space, considering the ring-bore structure interaction, bore distortion, ring-twist, piston secondary motion, non-Newtonian lubricant behavior, and ring/bore asperity contacts. The physics of the model includes the interface between the structure of the ring, oil lubricant, and the structure of the cylinder liner. The ring is modeled as a three-dimensional FEA model with the nodes along the ring circumference. The ring face orientation changes circumferentially depending on ring geometry as well as piston tilt angle and three-dimensional ring twist angle at every crank angle degree. The oil lubrication is modeled with the Reynolds equation with shear thinning and temperature dependent oil viscosity and with or without the flow factors. The cylinder liner description allows three-dimensional bore distortion and ring/liner asperity contact to be modelled. The key of the analysis is solving simultaneously at every crank angle increment a set of coupled linear and non-linear equations of ring structure, ring face lubrication, bore distortion, and asperity contact. The model predicts variations of the ring-pack lubrication in the axial and circumferential directions. Using the hydrodynamic lubrication model coupled with the asperity contact model allows calculations of the friction forces due to asperity contact (boundary and mixed lubrication) and oil film interactions (hydrodynamic and mixed lubrication). The transition from hydrodynamic lubrication to boundary lubrication through mixed lubrication is determined interactively based on ring / liner surface properties, ring loads, and lubrication properties. The new friction sub-module calculates axial and circumferential variation of both types of friction forces as well as total friction. The asperity contact induced friction forces and asperity contact pressure can further be used for ring wear calculations. The developed model has been applied to determine the performance of a production engine ring-pack. The influence of different phenomena affecting the ring-pack performance has been analyzed and compared.

Friction Reduction Opportunities in Combustion Engine Crank Train Bearings

2015 ◽  
Author(s):  
Rainer Aufischer ◽  
Rick Walker ◽  
Martin Offenbecher ◽  
Oliver Feng ◽  
Gunther Hager
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Combustion Engine ◽  
Operating Conditions ◽  
Friction Reduction ◽  
Viscosity Reduction ◽  
Oil Viscosity ◽  
Advantages And Disadvantages ◽  
Mixed Friction ◽  
Further Development

The development of combustion engines is heavily influenced by environmental regulations and efficiency. Since the environmental regulation have influenced engine design already with special combustion system and exhaust gas treatments, efficiency and the greenhouse gas CO2 has become a major issue for further development. CO2 emissions and fuel efficiency are linked and are directly influenced by the internal friction of the combustion engine. One major part of this internal friction is coming from the crank train bearings. Since we have to consider different operating conditions for the crank train bearings like hydrodynamic and mixed friction (hydrodynamic in combination with boundary contact), working principles as well as different engine operating conditions like full load, idle, start stop etc. different measures need to be employed for a friction reduced crank train. The optimal dimensioning of the bearings in combination with oil viscosity reduction are already known to a certain extent. Nevertheless they result in changes of bearing loads and may in consequence increase the share of boundary friction. Therefore, only looking on these two optimization steps is not enough. In addition the friction coefficient between bearing and shaft as well as the interaction between bearing surface and lubricant need to be addressed to reduce friction loss. In order to gain a complete picture, influences and the interaction of • geometric properties and bearing dimensions, • friction coefficient of bearings in combination with crankshaft materials, • oil formulation, viscosity and their interaction with engine application and duty cycle as well as • losses caused by the lubrication system design and components are investigated and analyzed based on simulation and testing. At first the different steps are investigated individually and secondly combinations and interactions are derived on basis of parameters derived on tribological tests and material data. Oil viscosity as major driver during hydrodynamic operation but also the influence of additive packages during mixed friction is roughly estimated on basis of tribological investigations. Since the overall friction system and its optimization are very complex, an example for a truck engine in different applications shows advantages and disadvantages of the different approaches. Also border lines given by operational risk and improvement limits are explained. The improvement options given by bearing materials and special coatings are explained in combination with different engines and engine applications. Further development activities, ways of collaboration between engine manufacturer and bearing supplier and an outlook on up-coming bearing system are completing the picture for a holistic approach on friction reduction in crank train bearings.

Effects of Liner Surface Texturing on Ring/Liner Friction in Large-Bore IC Engines

2006 ◽  
Author(s):  
Rosalind Takata ◽  
Yong Li ◽  
Victor W. Wong
Keyword(s):  
Film Thickness ◽  
Internal Combustion Engines ◽  
Surface Texturing ◽  
Friction Reduction ◽  
Asperity Contact ◽  
Oil Film ◽  
Surface Features ◽  
Flow Factor ◽  
Liner Surface ◽  
Ring Pack

Well-designed surface texturing may be used to reduce ring/liner friction and increase efficiency in internal combustion engines. This study investigated the effects of textures of either grooves or dimples on ring/liner friction, in the hydrodynamic and mixed regimes. Existing MIT models were used to conduct this research. The ring-pack model is based on averaged flow-factor Reynolds analysis, and is used in conjunction with a deterministic model for flow factor calculation. Although this advanced model is applicable in a wide range of cases, the surface textures studied here are very different than a typical liner surface, and can be represented only approximately by the averaged analysis upon which the ring simulation is based. For this reason, this analysis of surface features has focused on a parametric study, the goal of which is to analyze trends relating ring/liner friction to surface parameters, and to make a general evaluation of the potential of surface texturing to reduce ring-pack losses. In the hydrodynamic and mixed regimes, surface texturing affects the fluid pressure in the lubricant between ring and liner, thus affecting the ability of the oil film to support the ring load. If the effect of the texturing is to impede the flow of lubricant, the result will be an increase in oil film thickness. This causes friction reduction in two ways: if asperity contact was present, it is reduced; and the increase in film thickness causes a decrease in shear rate, thus decreasing oil shear stress. It was found that surfaces with both dimpled and grooved textures could cause friction reduction through this mechanism, with deeper features and more transverse groove patterns causing the greatest reduction. Friction also decreased with increasing area ratio (the percentage of the surface that is occupied by the surface features) for both grooves and dimples, and was only slightly dependent on groove width and dimple diameter. Because the effect of the surface texturing is on hydrodynamic effects in the oil, it is strongly coupled with lubricant properties. If surface texturing and lubricant viscosity are optimized together side effects such as oil consumption and wear can be mitigated, while friction can be reduced even further than it is via surface texturing alone. This possibility was also briefly considered in this study.

scholarly journals Mutual Effect of Groove Size and Anisotropy of Cylinder Liner Honed Textures on Engine Performances

2014 ◽  
Vol 966-967 ◽  
pp. 175-183 ◽  
Author(s):  
Mohammed Yousfi ◽  
Sabeur Mezghani ◽  
Ibrahim Demirci ◽  
Mohamed El Mansori
Keyword(s):  
Mutual Effect ◽  
Cylinder Liner ◽  
Texture Features ◽  
Groove Depth ◽  
Oil Consumption ◽  
Hydrodynamic Friction ◽  
Liner Surface ◽  
Ring Pack ◽  
Mixed Lubrication Regime ◽  
Cylinder Bore

The cylinder liner surface texture, widely generated by the honing technique, contributes a lot on engine functional performances (friction, oil consumption, running-in, wear etc.). In order to improve these functional performances, different honing processes are being developed. These different honing processes generate surfaces with various texture features characteristics (roughness, valleys depth, valley width, cross hatch angle, etc.). This paper addresses a comparison of ring-pack friction for cylinder texture with different cross-hatch angles and valley sizes. It takes in consideration the mutual effect of valley depth and honing angle. A numerical model is developed to predict friction within the cylinder ring-pack system in mixed lubrication regime and a morphological method is used to characterize groove depth. The results show the effect of different honing variables (rotation speed, stroke speed and indentation pressure) on cylinder bore surface textures and hydrodynamic friction of the ring-pack system.

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