Effects of lubricant viscosity on the mixed lubrication of a piston ring pack in an internal combustion engine

A theoretical analysis is presented of the mixed lubrication of a piston ring pack. The analysis comprises Patir and Cheng's average flow model and Greenwood and Tripp's asperity interaction model, and is developed to consider the shear thinning effect of a non‐Newtonian fluid, multigrade lubricant. The friction characteristics of the piston ring pack for both monograde and multigrade lubricants are investigated. It is found that a decrease in the lubricant viscosity is effective in reducing the friction loss, although this increases the boundary friction at the beginning of the expansion stroke. The friction characteristics are markedly affected by the shear thinning effect when multigrade lubricants are used.     

Numerical simulation of piston ring lubrication

This paper describes a numerical method that can be used to model the lubrication of piston rings. Classical lubrication theory is based on the Reynolds equation which is applicable to confined geometries and open geometries where the flooding conditions are known. Lubrication of piston rings, however, fall outside this category of problems since the piston rings might suffer from starved running conditions. This means that the computational domain where the Reynolds equation is applicable (including a cavitation criteria) is unknown. In order to overcome this problem the computational domain is extended to include also the oil film outside the piston rings.The numerical model consists of a 2D free surface code that solves the time dependent compressible Navier–Stokes equations. The equations are cast in Lagrangian form and discretized by a meshfree moving least squares method using the primitive variables u, v, ρ for the velocity components and density, respectively. Time integration is performed by a third order Runge–Kutta method. The set of equations is closed by the Dowson–Higginson equation for the relation between density and pressure. Boundary conditions are the non-slip condition on solids and the equilibrium of stresses on the free surface. It is assumed that the surrounding gas phase has zero viscosity. Surface tension can be included in the model if necessary. The contact point where the three phases solid, liquid, and gas intersect is updated based on the velocity of the solid and the angle between the normals of the solid and the free surface.The numerical model is compared with the results from an analytical solution of the Reynolds equation for a fixed incline slider bearing. Then results from a more complicated simulation of piston ring lubrication are given and discussed.     

Thermal effects in elastohydrodynamic lubrication of line contacts using a non-Newtonian lubricant

A Reynolds' equation, using Winer's viscoplastic model to express the non-Newtonian fluid property, is derived for line-contact EHL problems. The numerical solutions are obtained to the incorporated Reynolds', elasticity, and energy equations for pressure, film thickness, and temperature distribution between two surfaces simultaneously having rolling and sliding motions. The results are presented for thermal non-Newtonian lubrication, to observe the difference between Winer's equation and Trachman's expression on temperature distribution, pressure, and film thickness. The variation in friction coefficient with slip shear rate is in agreement with other experimental data.     

The non-Newtonian effect of temperature on hydrodynamic lubrication failure

The influence of temperature on the rheological characteristics of lubricants has been investigated by analysing the viscosity-temperature relationship and energy equation of lubricants. The constitutive equation, which describes the non-Newtonian properties of lubricants caused by thermal effects, is founded and coupled with equations of continuity and momentum of the fluid to calculate the load-carrying capacity in hydrodynamic lubrication. The numerical solutions show that lubricants have ultimate shear strength as a result of the non-Newtonian effect of temperature, which leads to the oil film having limiting load-carrying capacity. The mechanism of film failure in hydro-dynamic lubrication is also studied preliminarily in this paper.     

Analysis of the piston ring lubrication with a new boundary condition

Research on the inlet and outlet lubricational characteristics of the piston ring have been intense and ongoing. Many researchers had considered that the entire surface of the ring was enveloped in an oil film, but much experimental research has discovered that not all the entire surface was soaked. To consider a partially lubricated ring, the following conditions are presupposed; oil starvation is applied to the inlet region and the open-end assumption to the outlet region. This algorithm confirms flow continuity and permits the nadir of the pressure to go down to the saturation pressure. Using these new boundary conditions, the actual effective width participating in ring lubrication is determined and the minimum film thickness and flow rate for the ring pack can be calculated. The effective width is expected to be about 20 to 30 percent of the whole width of the ring, and the minimum film thickness is less than the result obtained by using the Reynolds cavitation boundary condition.     

The effect of lubricant inertia in hydrostatic thrust-bearing lubrication

The customarily neglected effect on the load capacity of hydrostatic thrust-bearings of the lubricant inertia is examined here for both liquid and gaseous lubricants. It is found that for liquid lubricants load capacities calculated by neglecting inertia can be significantly in error even at normal operating speeds. For gaseous lubricants the effect is the same for low recess pressures but tends to lessen at higher recess pressures.     

Effect of phyllanthus emblica biodiesel based lubricant on cylinder liner and piston ring

In the present time, need of biogenic lubricants is the focusing area which will be biodegradable, avirulent and eco-friendly. Current experimental tests depict the effect of ‘Phyllanthus emblica’ a non-edible feedstock through pin on disc tribo tester. Tests were conducted to evaluate the impact of 0, 10, 20 and 30 % blending of Phyllanthus emblica with SAE20W40 lubricating oil on cylinder liner and piston ring. Promising results have been manifested with 10 % blending of biodiesel (BD) with lubricating oil in terms of coefficient of friction and specific wear rate in comparison with other examined feedstock. For analysis of wear debris in the used oil analytical ferrography was also done. The effects of temperature on wear and friction characteristics have also been discussed.

     

影响无油润滑压缩机活塞环寿命的因素及对策

从使用和装配方面，分析了影响无油润滑压缩机活塞环寿命的因素，并对常见问题提出了对策。     

Calculation of mixed lubrication at piston ring and cylinder liner interface

This paper reports on the theoretical analysis of mixed lubrication for the piston ring. The analytical model is presented by using the average flow and asperity contact model. The cyclic variations of the nominal minimum oil film thickness are obtained by numerical iterative method. The total friction is calculated by using the hydrodynamic and asperity contact theory. The effects of the roughness height, pattern, and engine speed on the nominal minimum film thickness, friction force, and frictional power losses are investigated. As the roughness height increases, the nominal oil film thickness and total friction force increase. Also, the effect of the surface roughness on the boundary friction is dominant at low engine speed and high asperity height. The longitudinal roughness pattern shows lower mean oil film pressure and thinner oil film thickness compared to the case of the isotropic and transverse roughness patterns.     

Tribology of piston compression ring conjunction under transient thermal mixed regime of lubrication

Fuel efficiency is the main IC engine attribute, with the compression ring-bore contact consuming nearly 5% of the fuel energy. Analyses are often idealised, such as isothermal condition and smooth surfaces, the former being particularly contrary to practice. An analytic solution to the average flow model is presented for this contact with a new analytical thermal model. The generated contact temperatures, particularly at the inlet result in thinner films than the idealised analyses. For the simulated city driving condition the power loss is mainly due to viscous shear under cold engine condition, whilst for a hot engine boundary friction dominates.     

On the effective length of the top piston ring involved in hydrodynamic lubrication

This paper describes a simple analytical model for top piston ring lubrication. The model is constructed using the open‐end boundary condition hypothesis, with an assumption of minimum hydrodynamic pressure in the effective ring length equal to the saturation pressure. The analysis confirms that not all of the ring length is involved in the case of hydrodynamic lubrication, and the effective length is found to be less than 40–50% under some operating conditions. The results are in agreement with previous investigations.     

Elastohydrodynamic lubrication of piston rings

A non-linear finite-element scheme, based on the Newton-Raphson-Murty algorithm, was used to analyze the problems of piston rings according to theories of both elastohydrodynamic and hydrodynamic lubrication. The maximum film pressure and the minimum film thickness were obtained and depicted as functions of the crank angle. For hydrodynamic lubrication the results obtained were compared with those found using the method suggested by Dowson and Ruddy; there was good consistency between them. In this way the accuracy and reliability of the proposed method are demonstrated. Furthermore, the results evaluated using the theory of elastohydrodynamic lubrication give a larger minimum oil film thickness and a flatter pressure distribution than those evaluated using the theory of hydrodynamic lubrication.     

The effect of a friction modifier on piston ring and cylinder bore friction and wear

The addition of friction modifiers to crankcase lubricants has been shown to significantly reduce the mechanical losses of critical components in internal combustion (ic) engine; thereby improving fuel economy.In this study the friction and wear of a piston ring/cylinder bore material combination was studied using a pin-on-plate laboratory tribo-test machine developed to reproduce the wear mechanisms encountered in an ic engine. Two lubricants were evaluated: (i) a standard SAE 30 grade diesel formulation, and (ii) the same formulation with the addition of a 5% soluble MoS₂ friction modifier.Analysis of the wear results identified three periods of wear: (1) running-in, (2) transient wear and (3) terminal wear. Throughout this study particular emphasis has been placed on the simulation of the wear mechanisms occurring within engines. Surface analysis confirmed that both abrasive wear and delamination wear was produced.Friction benefits attributable to the addition of MoS₂ friction modifier were obtained. However, under specific conditions the wear rate increased due to increased abrasion of the plate.     

中凸型活塞裙部的流体动力润滑分析

结合动力学方程及活塞裙部在缸套内的流体动压润滑方程,运用数值方法研究活塞的二阶运动,分析中凸型线对活塞裙部无量纲位移等方面的影响.通过与直线型线对二阶运动影响结果比较发现,中凸型活塞裙部更利于运转性能的提高.     

Friction characteristics of piston ring pack with consideration of mixed lubrication: Parametric investigation

This paper reports on the friction characteristics of a piston ring pack with consideration of mixed lubrication. The analytical model is presented by using the average flow and asperity contact model. The effect of operating condition, and design parameters on the MOFT, maximum friction force, and mean frictional power loss are investigated. Piston ring pack shows mixed and hydrodynamic lubrication characteristics. From the predicted results, it was fand that the ring tension and height of surface roughness have great influence on the frictional power losses in a ring pack. Especially, ring tension is a dominant factor for the reduction of friction loss and maintenance of oil film thickness.     

Thermo-elasto-hydrodynamic lubrication analysis of piston skirt considering oil film inertia effect

Influence of oil film inertia forces on thermo-elasto-hydrodynamic lubrication performances of a piston skirt is analyzed, based on a proposed Reynolds lubrication equation for the consideration of oil film inertia force effects. Further, a scheme to solve the inertia effects is given. The numerical results show that oil film inertia forces can result in increments in film pressure and temperature, hydrodynamic friction force and load capacity, deformation, and transverse displacements of the piston skirt. Moreover, the influences are obvious for a big reduced Reynolds number. Therefore, oil film inertia force effects on thermo-elasto-hydrodynamic lubrication performances of a piston skirt in a high speed internal combustion engine should be considered.     

The influence of the viscoplastic and viscoelastic character of a lubricant on elastohydrodynamic lubrication

The non-newtonian constitutive equation proposed by Johnson and Winer is discussed. Derivations of the lubrication equations suitable for the viscoplastic rheological model and the viscoelastic model are presented. The full numerical elastohydrodynamic lubrication solutions for the viscoplastic model and the viscoelastic model are obtained in order to observe the effects of the elastic shear modulus of the fluid and the limiting shear stress on the pressure distribution, film thickness and coefficient of friction.     

活塞环润滑状态的分析与应用

应用雷诺方程描述了内燃机中活塞环的润滑状态,在数学模型中考虑了表面形貌,给出了描述表面形貌的数学表达式,从而可定量地分析粗糙度方向与粗糙峰高对润滑状况的影响。应用有限差分法及数值迭代对修正后的雷诺方程进行了求解,讨论了相关因素对油膜厚度的影响,总结了它们对汽车应用产生的影响。     

Effect of non-Newtonian lubrication on the separation of a sphere from a flat

A numerical analysis is presented to study the effect of lubrication with non-Newtonian fluid on the separation flow of a fully flooded sphere from a flat under the condition of constant applied load. Different non-Newtonian fluid models were utilized to account for the microstructure and rheology of additives suspended in the film lubricant, namely those models for couple stress, micropolar, and power-law fluids. The equation of motion of the sphere was used to examine the effect of the sphere inertia on accelerating the separation process as the film viscous force decreases. This required solving the film pressure field, which is derived from a modified Reynolds equation and later computed numerically by a forth-order Runge-Kutta integration scheme. Several parameters were examined such as the time to complete separation, the length scale of the additives, the variation in lubricant's viscosity due to the presence of the additives, the sphere mass and radius, and the applied force on the sphere. Compared to the Newtonian fluid case, the results of the numerical solution indicated that there is a delay on the separation time for large non-Newtonian parameters, i.e., parameters representing additives characteristic length, additives concentration, and power-law indices.