This paper describes that an analysis of oil film thickness on a piston ring of diesel engine. The oil film thickness has been performed by using Reynolds equation and unsteady, two-dimensional (2-D) energy equation with a heat generated from viscous dissipation. The temperature distribution in the oil film is calculated by using the energy equation and the mean oil film temperature is computed. Then the viscosity of oil film is estimated by using the mean oil film temperature. The effect of oil film temperature on the oil film thickness of a piston ring was examined. This model has been verified with published experimental results. Moreover, the heat flow at ring and liner surfaces was examined. As a result, the oil film thickness could be calculated by using the viscosity estimated from the mean oil film temperature and the calculated value is agreement with the measured values.

The wear of piston rings in the diesel engines with EGR system is studied experimentally. In order to clarify the effect of PM on the wear, the wear of the piston rings in the test engine is measured, (1) when the non-soluble in the lubricating oil is removed by the oil filters, (2) when PM in the re-circulating gas is removed by the DPF, (3) when the carbon black is added in the lubricating oil. The experimental results are discussed with the measured time history of kinematic viscosity, total base number, total acid number, ZDTP survival rate, and carbon residual content and its particle size in the engine oil.

Both the piston ring and cylinder bore experience wear throughout their life cycle. Therefore change occurs in the geometrical profile and topography of the ring. In addition, coating on the ring is also subject to wear, thus altering the physical/mechanical property of the contacting surface. These changes affect the tribological performance of the ring-bore conjunction. Geometrical changes often alter the ring contacting profile, which affects the entrainment of the lubricant into the conjunction. This can affect the regime of lubrication, thus mechanisms that contribute to friction. Wear of surfaces also plays some role in boundary friction in terms of topographical changes as well as surface properties such as hardness and asperity shear strength. Most analysis does not take into account changes in tribological conditions which occur as the result of these salient changes in practice. The paper intends to bridge this gap in the fundamental knowledge and provide explanations for some in-field experiences noted with wear of a compression ring in a typical engine test. The method of solution used is based on the average flow factors which are indicative of entrainment of the lubricant through the rough ring-bore conjunction. This approach was initiated by Patir and Cheng, for which realistic topographical parameters according to the stage of the wear process is included. Changes in friction and fuel energy consumed are predicted.

The continuous focus on improving engine efficiency and fulfilling new emissions legislations in high speed large bore (HSLB) applications is demanding higher performance of cylinder power cell. Regarding piston rings, this can be translated into the need for increased wear and scuff resistance in conjunction with low friction. However, there is no room to jeopardize the engine performance in terms of lube oil control and combustion gas sealing (i.e. blow-by). The reduction in ring friction is linked with three main factors: reduction of ring tangential load, reduction of ring axial width and use of low friction coefficient materials. To enable load and axial width reduction the use of a steel ring pack becomes almost mandatory. The structural strength of steel is needed in the narrower cross-section which at the same time requires good resistance to temperature and loads. For better wear resistance and lower friction coefficient the use of improved materials is important on all three rings in the pack. The improved performance of nitriding treatment and CrN PVD coatings will be presented. Results indicate a potential ring friction reduction of more than 30% combined with wear improvements of up to 50% depending on the engine operation. Evaluations of rig and engine tests are presented supporting the technical case.

Advances in modern engine development are becoming more and more challenging. The intense increase of thermal and mechanical loads interacting in the combustion chamber as a result of higher power density requires perfecting the function of piston rings especially with regard to emission reduction technology. The major obstacle to predicting blow-by and oil consumption is the behavior of the piston rings under engine operating conditions. Design and functionality of a piston ring are highly influenced by the operating conditions. To understand the fundamentals of ring behavior and in this way the effects on blow-by and oil consumption, an analytical tool has been developed to transform the physical boundary conditions of engine kinematics and ring design into a reliable simulation. This paper describes the physical basics of ring movement under dynamic loading conditions and gives an overview of the results. It also was necessary to validate the model with real engine measurements to understand the fundamentals of ring design as a function of the described mathematics.

Diesel engine technology advancements in performance and requirements for meeting emission regulations have developed new challenges for piston system durability. Increased combustion pressure and exhaust gas recirculation have severely increased the demand of the top piston ring to top piston groove surface interactions. This more demanding environment has resulted in new needs for improved durability and compatibility of the bottom flank of the top piston ring and the bottom side to the top piston groove. Developments in materials and treatments of these surfaces require accurate analysis and assessment of the worn regions. With this demand, new measurement techniques have been deployed to accurately map the bottom flank of the top piston ring and the bottom side of the top piston groove. The new methods allow for volumetric wear measurements and regional analysis for wear step magnitudes to assist in better material wear characterization as well as piston ring design influence.

Facing monumental challenges in the tightening constraints of friction reduction, oil control, and blowby, piston ring designs are becoming intricately more complex. Within this complex matrix of design criteria, minute changes can have a big impact on the performance of engines, which are operating under conditions of higher temperatures and speeds. At the same time there is a general requirement to reduce the overall mass of the components. Thus, the piston rings must have inherent design properties (more finely tuned) to withstand the elevated operations of the engine, maintain longevity, and perform within the expected performance criteria. To help meet these challenges, this paper gives a brief introduction to the axial formed process as an improvement of the twist characteristic on the upper compression ring (UCR) design, along with representative supporting performance data based on engine tests and computer simulation. The goal is to show some successes across different engine types involving the axial formed process. The main topics covered include a) historical role and design of twisted rings in the engine, b) advantages of improved twisted rings, c) example of engine test data and d) example simulation results.

Micro-dimples on the surface of lubricated sliding contacts can act as mini-hydrodynamic bearings. The pressure generated within these dimples tends to separate the surfaces and reduce the number of asperities in contact, thereby lowering the average coefficient of friction and moving the lubrication condition to the more stable hydrodynamic lubrication regime. An experimental study on the effects of laser surface modifications for friction reduction is presented through the use of several experimental test rigs. Micro-dimples were generated with an Nd-YAG laser on the surface of flat samples for testing in constant speed and reciprocating motion test rigs. These simple geometries were used to investigate the phenomenon and validate existing analytical models. Modifications to the top dead center region of an actual cylinder liner were evaluated with a motored, small-engine dynamometer. The results demonstrated that measurable friction reductions can be achieved using this approach.

A project to reduce frictional losses from natural gas engines is currently being carried out by a collaborative team from Waukesha Engine Dresser, Massachusetts Institute of Technology (MIT), Colorado State University (CSU), and ExxonMobil. This project is part of the Advanced Reciprocating Engine System (ARES) program led by the US Department of Energy. Changes in lubrication oil have been identified as a way to potentially help meet the ARES goal of developing a natural gas engine with 50% brake thermal efficiency. Previous papers have discussed the computational tools used to evaluate piston-ring/cylinder friction and described the effects of changing various lubrication oil parameters on engine friction. These computational tools were used to predict the effects of changing lubrication oil of a Waukesha VGF 18-liter engine, and this paper presents the experimental results obtained on the engine test bed. Measured reductions in friction mean effective pressure (FMEP) were observed with lower viscosity lubrication oils. Test oil LEF-H (20W) resulted in a ∼ 1.9% improvement in mechanical efficiency (η mech ) and a ∼ 16.5% reduction in FMEP vs. a commercial reference 40W oil. This improvement is a significant step in reaching the ARES goals.

A new measuring technique has been developed in order to determine the oilfilm thickness between piston ring and cylinder liner in a combustion engine by use of laser-induced fluorescence (LIF) technique. In clear contrast to further investigations, where optical probes have been mounted at a fix position in the cylinder liner allowing single measurements at defined times of the piston stroke, only, the optical probes used in the presented work are mounted in the piston and the piston ring. Fiber optics, led via a grasshopper-link, carry the exciting laser radiation (λ = 488 nm) to the probes and backwards the fluorescence radiation (λ ∼ 540 nm) to a photomultiplier. Thus, the developed measuring system allows a continous, crank-angle resolved measuring of the oilfilm thickness. As the LIF-technique is a relative measuring technique, calibration work, especially in the combustion engine, had to be done. Using eddy current sensors at a fix position in the cylinder liner the oilfilm in a single point could be determined. Grooves of defined depth in the cylinder liner provided the fluorescence signal amplification in each stroke so that adverse influences of oil pollution or temperature could be eliminated. A method has been developed to eliminate transmission influences contributed to the grasshopper link system. The measuring technique adapted to a single-cylinder SI engine has been tested under motored and fired conditions. Parameters under motored conditions were engine speed, oil- and coolant-temperature and throttle position. Experiments under fired conditions (part load) have been done varying oil and coolant temperature. Correlations between oilfilm thickness and HC-emissions under motored conditions have been found. Incylinder pressure, oil-temperature and engine speed are the most influencing parameters.

The role of cylinder bore shapes in engine performance has been the subject of several studies in recent years. In particular, the influence of bore distortion on oil consumption under high speed conditions has generated significant interest. In this paper, the effect of an axial bore profile on radial dynamics of a ring is investigated. Radial ring motions within grooves due to the axial bore profile can generate significant inertial effects and also have an impact on ring end-gap sizes and lubrication conditions at the ring-liner interfaces. The magnitude of such effects is dependent on the ring-pack configuration, engine operating conditions (speed and load) and axial bore profile details. These issues are investigated in this study due to their implication on engine oil consumption, friction and blow-by. The authors have developed an analytical expression to account for the effects of radial ring inertia due to an axial bore profile for implementation in a piston ring–pack simulation tool RINGPAK. Simulation results from a gasoline engine study are presented to illustrate the effects of engine speeds, ring tensions and characteristics of axial bore profiles on ring radial dynamics and ring-liner lubrication. Relevant qualitative comparisons are made to experimental measurements available in the literature.

The cylinder-kit assembly of an internal combustion engine experiences severe conditions during engine operation. The top compression ring, in particular, undergoes extreme stress directly from cylinder gas pressure, inertial and thermal loads. The top compression ring is often the most significantly affected piston ring, and one of the common resultant phenomena is high wear on the ring/bore surfaces. In many previous studies, the modeling of tribological phenomena at the top compression ring/bore region involves hydrodynamic and boundary lubrication, friction and wear. This present work accounts for an additional factor that may affect the piston ring/bore lubrication — the lubricant evaporative effect. A three-dimensional oil evaporative analysis is coupled into the calculation of mixed lubrication in a cyclic engine computation. The presence of the evaporation analysis allows the study of the temperature influence on the piston ring/bore lubrication in addition to its effect on oil viscosity. A prospective application of this model is in diesel engine analysis. Considering the broad operating range of modern diesel fuel injection systems, the injection timing can be made throughout the compression/expansion process. It is well demonstrated that certain areas of fuel injection operation can result in potential adverse consequences such as increased bore wear. A well known example is “bore wall fuel wetting.” Given concerns around the potential for wear-inducing interactions between the fuel injection plumes and the bore wall, we have explored a particular interaction: bore wear in response to an imposed local heating of the bore wall. The simulation result provides valuable insights on this interaction, in which higher bore wear is predicted around bore wall area with locally imposed wall heating.

This paper presents an investigation into the characterization and performance prediction of different cylinder liner surfaces commonly used in modern internal combustion engines. The topography of liner specimens was measured, and the friction and wear between a piston ring and each liner surface was measured using a horizontal reciprocating bench tester. The load, speed, and lubricant supply during testing were chosen to ensure that the piston ring and liner operated primarily in a mixed lubrication regime. A computer program was developed to model the performance of the piston ring and liner specimens under the conditions observed during the reciprocating bench test. The Greenwood and Tripp statistical asperity contact model was employed to describe the rough surface contact behavior between the liner specimen and piston ring. Two different methods of characterizing the liner specimen surface roughness and determining the inputs required for the Greenwood and Tripp model from the surface measurements were considered. The friction observed experimentally was compared to the friction predicted by the model, and the ability of the model to predict the absolute friction for a given surface and the relative difference in friction between two different surfaces was investigated.

The influence of piston ring lubrication on internal combustion engine performance has received considerable attention for over half-century. Studies show that hydrodynamic lubrication prevails through most of engine cycles, and asperity contact only occurs near the vicinity of dead centers [1][2]. In order to solve the governing equation of lubricant, appropriate velocity and pressure boundary conditions should be incorporated into the lubrication equation - Reynolds equation. While lubricant obeys the no-slip velocity boundary condition, the pressure boundaries at the leading and trail edge of piston ring are related to the chamber and the inter-ring crevice gas pressures. A complete lubrication analysis of piston ring requires an inter-ring gas flow model. In most of existing lubrication models, an isentropic orifice flow model is adopted and the gas flow is assumed to an ideal gas passing through the piston ring end gaps with a constant discharge coefficient [2][3][4][5]. In additional to the flow path of piston ring end gaps, gas also flows through the side-clearance between piston ring and flank groove [6][7][8][9][10]. In this paper, a quasi-Rayleigh narrow-channel gas flow model is proposed by consideration of temperature gradient along radial direction of piston assembly. Piston ring friction force is estimated by a test-rig verified mixed lubrication model [11]. Numerical simulation shows that piston ring friction force and ring axial motion are sensitive to inter-ring gas flow model. The instantaneous indicated mean effective pressure (IMEP) method was adopted here to measure the piston friction during motoring condition. Experimental and numerical results indicate that top ring could contribute about 10% of total power cylinder friction loss.

In diesel engines, transient heat transfer in the piston/rings/liner system greatly affects the performance of the engine, such as in carbon deposit buildup, microwelding, lubricant degradation, and changing mechanical properties of the materials. The current work aims at studying the local piston/rings/liner transient heat-transfer process by incorporating real time dynamics of the rings in sufficient detail. In the present study, several techniques have been adopted to simulate the transient heat transfer process, with fully-incorporated ring dynamics. These techniques include using the model/submodel approach, local refined mesh approach, and the virtual thermal conductivity approach. The transient temperature and heat flux profiles in the piston and rings are illustrated. The results show that the relative movement of the rings greatly affects the temperature/heat flux distribution and the peak temperature in the top ring. The friction heating between the top ring and the liner is also evaluated. The analysis demonstrates that under some extreme conditions when frictional heating reaches its peak value, some heat flux directs back to enter the ring.

This investigation was aimed to investigate the effect of Exhaust Gas Recirculation (EGR) on wear of in-cylinder engine parts. EGR setup was fabricated for a two cylinder, air cooled, constant speed direct injection CI engine. Test setup was run for 96 hours with fixed loading cycles in two phases; normally operating condition (i.e. without EGR) and with 25% EGR rate. Addition of wear metals in the lubricating oil was investigated. Higher wear metal concentrations were found in the lubricating oil of EGR operated engine, which indicates higher wear of various engine parts. Weight loss of piston rings used in both the phases was compared to quantify the amount of wear of piston rings. To quantify the amount of wear of surface of cylinder liners, surface roughness parameters were measured at three positions (TDC, mid stroke, and BDC) on thrust and anti-thrust side. A qualitative analysis was also carried out by surface profiling and Scanning Electron Microscopy (SEM) at same locations.

There must be an end gap in the piston ring because of the need of mounting and compensation for diameter after the wear of ring. Richardson’ and many author’ studies have showed the effects of the end gap to blowby and oil consumption, especially in the presence of ring or liner wear. This problem has influenced the effective utilization of the fuel energy for many years. Moreover the ring will rotate in the working cycle of engine. Once the end gaps of two compression rings come to the site of superposition, the shortest passage of gas flow is formed and blowby will be increased. The deflection of crankpin and rotation of piston were calculated according to the analytical model based on the torque transmission theory of crankshaft. The positive and negative deflections of crankpin result in the reciprocating rotation of piston in the IC engine working cycle. The peak values of deflection and rotation are in the vicinity of crank angle position of deflagration. Because the clingy moment of compression rings are less than rotational resistance moment in a few section of crank angle, they are unable to keep synchronism with piston and the rotations opposite to piston occur. The rotation angle of the second compression ring is more than that of the first ring. The superposition of the end gaps of two compression rings comes about when they turn to the same angle position. Based on above study, the structure of one compression ring in piston system should be widely used, which is in favor of reduction of friction and engine weight, pushing forward the lightweight process, being useful to the decrease of fuel consumption and emission. The pressure of combustion gas will not remarkably descend in this structure. The problem of ring suspension and pressure release in the first ring land can be resolved. Two types of rings with complete seal and economizing energy design are showed for the structure of one ring, which will also avoid the increase of end gap after the rings are worn.

A project to reduce frictional losses from natural gas engines is currently being carried out by a collaborative team from Waukesha Engine Dresser, Massachusetts Institute of Technology (MIT) and Colorado State University (CSU). This project is part of the Advanced Reciprocating Engine System (ARES) program led by the US Department of Energy. Previous papers have discussed the computational tools used to evaluate piston-ring/cylinder friction and described the effects of changing various ring pack parameters on engine friction. These computational tools were used to optimize the ring pack of a Waukesha VGF 18-liter engine, and this paper presents the experimental results obtained on the engine test bed. Measured reductions in friction mean effective pressure (FMEP) were observed with a low tension oil control ring (LTOCR) and a skewed barrel top ring (SBTR). A negative twist second ring (NTSR) was used to counteract the oil consumption increase due to the LTOCR. The LTOCR and SBTR each resulted in a ∼ 0.50% improvement in mechanical efficiency (η mech ).

An unsteady and two-dimensional thermohydrodynamic lubrication model in consideration of the ring movement and the heat flow from ring groove to piston ring was developed. The piston ring temperature in an internal combustion engine was analyzed by using the unsteady and two-dimensional form heat-conduction equation in consideration of axial movement of ring and heat flow from ring groove to ring during a cycle. The oil film temperature, oil film thickness and heat transfer between ring and liner surfaces were analyzed by using the calculated ring temperature taking into consideration cycle variation. The results are as follows. The heat flow rate around ring changes greatly with the ring movement and the ring sliding face temperature changes about 6 °C in a cycle. Then, the cycle mean temperature of ring sliding face becomes lower than the ring sliding face temperature calculated by the ring groove and liner surface temperatures under 2800 rpm and full load conditions. Therefore, the oil film viscosity is higher than that of the conventional viscosity model in which the viscosity was based on a constant ring sliding face temperature in a cycle. The oil film thickness predicted by the present method is thicker than that calculated by our previous method.