Oil Control Ring Research Articles

The Effect of Ethanol Fuel-Diluted Lubricants on the Friction of Oil Control Ring Conjunction: A Combined Analytical and Experimental Investigation

This paper presents an investigation of the frictional behaviour of three-piece piston oil control rings. A bespoke tribometer replicates the kinematics of the contact between a full oil control ring and the cylinder liner. The three-piece oil control ring is composed of two segments, separated by a waveform-type expander. The experimental results indicate the dominance of a mixed regime of lubrication throughout the stroke. This is particularly the case when the experiments are conducted at 80 °C, a typical engine sump temperature, when compared with those at 20 °C (a typical engine start-up temperature in the UK in the summer). A mixed hydrodynamic analytical model of the oil control ring–cylinder liner tribological interface is employed to apportion frictional contributions with their physical underlying mechanisms. Therefore, combined numerical and experimental investigations are extended to lubricant contamination/dilution by ethanol-based fuels. This study shows that the transition from E10 to E85 would have an insignificant effect on the friction generated in the oil control ring conjunction. This holistic approach, using a detailed predictive l mixed regime of lubrication model and a representative bespoke tribometry, has not hitherto been reported in the open literature.

A Study on the Oil Film Thickness Between the Lower Rail of Oil Control Ring and Lower Flank of Oil Control Ring Groove of an Engine

Abstract Lubricating oil consumption (LOC) of engines causes particulate matter in exhaust gas and abnormal combustion like pre-ignition which becomes a serious problem in hydrogen engines. Lubricating oil transports upward into the combustion chamber of an engine via the sliding surface, the gap, and the side and back of a piston ring. The target of this study was to clarify the mechanism of oil flowing between an oil control ring lower flank and the groove which was the first entrance of lubricating oil supplied from the crankshaft. Oil film thickness at the lower flank of the oil control ring was measured by laser-induced fluorescence method using optical fibers embedded in the lower flank of the ring groove. The measured oil film thickness was compared with forces acting on the lower rail of three-piece type oil control ring. The oil film thickness change was well explained using those forces and it was found that friction force at the sliding surface and pressure in the ring groove were dominant on the oil film thickness under all operating conditions tested in this study.

On the Role of Friction Modifier Additives in the Oil Control Ring and Piston Liner Contact

Abstract In-cylinder internal combustion engine parasitic frictional losses continue to be an area of interest to improve efficiency and reduce emissions. This study investigates the frictional behavior at the oil control ring–cylinder liner conjunction of lubricants with anti-wear additives, varying dispersant concentration, and a range of friction modifiers. Experiments are conducted at a range of temperatures on a cylinder liner with a nickel silicon carbide coating. A novel motored reciprocating tribometer, with a complete three-piece oil control ring and cylinder liner, was used to isolate the friction at the segment–liner interfaces. Four lubricants were tested, three with the same 3% dispersant concentration and 1% zinc dialkyl dithiophosphate (ZDDP) anti-wear additive: the first with no friction modifier, the second with inorganic friction modifier (molybdenum dithiocarbamates), and the third with organic friction modifier (amide). A fourth lubricant with an organic friction modifier with a 9% dispersant concentration was tested to compare the effect of the level of dispersant with the friction modifier. Results indicate that the inorganic friction modifier reduces friction comparatively to the other lubricants, showing the importance of friction modifier selection with anti-wear additives.

Sources and Destinations of Oil Leakage through TPOCR Based on 2D-LIF Observation and Modeling Analysis

The Three-Piece Oil Control Ring (TPOCR) is becoming a viable option for heavy duty gas and hydrogen engines due to the low particle concentration in these engines. Although direct oil leakage from the gap is not likely to happen with the misalignment of the upper and lower rail gaps, there exist other less-apparent oil leaking mechanisms through the TPOCR. This work is targeted at understanding the oil leakage’s source and destination through the rail and liner interfaces across the whole cycle. The 2D Laser Induced Fluorescence technique was applied on an optical engine to study the oil transport behavior. Combined with a TPOCR model for dynamics and lubrication, the mechanisms that cause rail twist and oil scraping by the upper rail were analyzed. It was found that the symmetrical rail can scrape the oil up in the up-strokes. The scraped oil first accumulates in the clearance between the upper rail and groove, as well as at the upper corner of the rail Outer Diameter before being transferred to both the third land and liner when the piston changes direction at Top Dead Center. Rails with an asymmetrical profile can reduce or enhance these effects depending the orientation of the rails. This study provides findings that could help design the engine to better control Lubricate Oil Consumption and properly lubricate the Top Dead Center’s dry region at the same time.

Experimental Investigation of Oil Transport during Low Load to High Load Transient in Internal Combustion Engines

Reducing the Lubricating Oil Consumption (LOC) has been a critical focus for engine manufacturers. LOC not only depends on engine operating condition but also the history of the operating condition variations. This work seeks to understand the oil transport in the ring pack during the low load to high load transient through experimental investigations. An optical engine with 2D Laser Induced Fluorescence (2D-LIF) technique, equipped with a modern low-tension Three-Piece Oil Control Ring (TPOCR), was applied to investigate the oil transport in the ring pack. It was found that, after the engine stayed under the blowby separation line long enough, a sudden increase to high load can result in a huge increase of oil ejection to the liner from the top ring groove in the expansion strokes. The mechanism behind it is that, when the load is increased, the oil accumulated inside the top ring groove during the low load condition is pushed out by the gas flow after the peak cylinder pressure is reached. Different combinations of load, speed, rate of change in load and time duration at low load were tested to examine their influence on this leakage mechanism. An operation with a gradual increase of engine load was found to be able to reduce the amount of oil leaked to the liner by releasing more oil to the second land. These findings can help the effort to reduce the oil emission (OE) generated from Spark Ignited (SI) engines equipped with TPOCR in the real-world transient driving conditions as well as the emission tests.

Effect of Blowby on the Leakage of the Three-Piece Oil Control Ring and Subsequent Oil Transport in Upper Ring-Pack Regions in Internal Combustion Engines

The lubricating oil consumption (LOC) in internal combustion engines contributes to emission and deteriorates the performance of the aftertreatment. In this work, an optical engine with a 2D Laser-induced fluorescence (2D-LIF) system was used to study operating conditions critical to real driving oil emissions. Additionally, numerical models were used to analyze the ring dynamics, oil flow and gas flow. It was found that the intake pressure that results in zero blowby is the separation line between two drastically different oil flow patterns in the ring pack. With intake pressure lower than the separation line, the oil accumulation of the three-piece oil control ring groove (TPOCR) begins to increase, followed by the drastic increase of the oil accumulation in the third land, second land, and finally visible oil leaking through the top ring gap, given enough time. The time required for the oil to leak through different rings was investigated using both measurements and modeling. The effects of drain holes and rail gaps, as well as their relative rotation on oil accumulation and leakage from the TPOCR groove, were analyzed. These findings contribute to improving ring pack designs and engine calibration in spark ignition (SI), gas, and hydrogen engines equipped with TPOCR to minimize the negative impacts of LOC.

Multi-objective Optimization and Sensitivity Analysis of the Parameters Affecting Sealing Performance of the Piston Rings Face through the Validated Model for the Four-stroke Bi-fuel Engine

A multi-objective optimization study and sensitivity analysis of a SI engine piston-rings pack using dynamics analysis software (AVLExcite Piston&Rings) and optimizer software (modeFRONTIER) are presented. The effects of changing the piston rings' tangential force and face profile on the oil and gas flow behavior inside the piston-rings pack are investigated by calculating the lubrication oil consumption, blow-by, and power losses. The feasibility of the simulation model was determined by comparing it to empirical data obtained from experimental testing of the engine to estimate the amount of oil consumption and blow-by gas flow. Using the statistical modeling algorithm SS-ANOVA, multi-objective optimization investigates the individual and interaction effects of the three rings' tangential forces. This method significantly reduces the time and cost required to find the optimal design, an approach not reported in previous studies. The results showed a strong correlation between simulation and experimental test results, indicating an acceptable match during model validation. Furthermore, the predictions show that tangential forces affect sealing performance; thus, modifying the tangential force resulted in a 30% reduction in oil consumption and less than a 0.8 percent increase in friction. Furthermore, the LKZ oil control ring model efficiently reduces oil consumption by 25% while slightly increasing friction (about 10 percent without face coating).

Piston ring oil film thickness measurements in a four-stroke diesel engine during steady-state, start-up and shut-down

Internal combustion engine research predominantly focuses on routes to lower emissions to meet various emission legislation. Lower emissions can be achieved with increased fuel efficiency and less lubricant throw off/lubricant combustion in the piston ring zone. These are all dependent on the oil film that forms between the liner and piston components. This article details the use of ultrasonic sensors to study the lubricant film thickness between the engine liner and piston rings/skirt in a fired diesel two-cylinder YTR engine. The testing regime covered a series of engine speeds and loading levels and found the minimum oil film thickness to vary from 1 to 3.5 μm. Spectrograms (time-varying ultrasonic amplitude spectra) have shown a residual oil film on the liner, first present after the skirt moves above the sensor that peaks at 440 μm, which then dissipates until the next oil control ring passage. Start-up and shut-down captures have visualised the build-up and reduction of the film thickness, in which during start-up typically a 2-s interval between the first ring passage and a consistent film thickness was seen. Whilst the shut-down tests showed a lesser variation, anticipated to be due to the oil pump already operating and is, therefore, less subjective to a reduction in engine speed providing a threshold of oil remains on the liner. Measurements like this help to describe how lubrication occurs in the piston ring zone and hence can optimise component design and an oil injection schedule.

Prediction and Experimental Verification for Oil Transport Volume around Three-Piece Type Oil Control Ring Affecting Lubricating Oil Consumption

<div class="section abstract"><div class="htmlview paragraph">Reducing of lubricant oil consumption (LOC) remains a major issue for internal-combustion engines. Especially in recent years, in order to comply with Particular Number (PN) regulations and lower oil viscosity to reduce friction loss, need to reduce the LOC has increased. Controlling the upward oil flow, that passes the piston and piston rings, is effective in reducing the LOC. In addition, oil control ring (OCR) has significant effect on upward oil flow. Therefore, development of a high-precision prediction method of oil behavior around the OCR is important for prediction of LOC. So, the model of Three-piece type oil control ring (3POCR) motion within the OCR groove and the model of oil behavior around the 3POCR were developed using the computer aided engineering (CAE) method in this paper. These models calculate in detail the upward oil outflow to the 3rd land from the OCR groove, which is based on the relation between the OCR motion and the gas pressure as well as the inertial force of oil. Since factors that greatly affect the prediction accuracy are the gas pressure around the OCR and the OCR motion, these were measured and verified in the actual engine. Furthermore, oil behavior observation using in-cylinder visualization engine, and oil film thickness measurement using optical fiber were conducted for experimental verification of the oil behavior model around the 3POCR. As a result, qualitative tendency of calculated results and measured results showed good agreement. Also, comparison in two different OCR specification, the similarly tendency was obtained. Therefore, the effectiveness of the developed prediction model was confirmed.</div></div>

An experimental investigation of low viscosity lubricants on three piece oil control rings cylinder liner friction

Reducing energy use and improving engine efficiency is a complex task however to date a continued reduction of lubricant viscosity has proved effective. Reducing viscosity decreases hydrodynamic friction and pumping losses however it can also exacerbate boundary friction losses. Detailed and representative component level experimentation is required to understand the effects of viscosity reduction on friction and opportunity for further optimisation. This paper presents a novel motored reciprocating Tribometer which has been developed to measure the friction between complete cylinder liners and three-piece oil control rings. The system holds individual or multiple rings stationary in a bespoke ring holder and reciprocate the cylinder liner thereby replicates the relative kinematics of the components in service. The new design has many operational advantages to identify and benchmark the individual contribution of oil control ring friction including near total isolation of oil ring-cylinder liner bore conjunction, pure rectilinear motion and use of full components without resorting to split liner/ring geometries. The experimental rig is used to measure friction at the three-piece oil control ring- cylinder liner conjunction when lubricated with two low viscosity lubricants. The results show prevalence of mixed regime lubrication across the speeds, temperatures and lubricants investigated. The oil control ring under investigation is shown to operate in mixed regime lubrication and at cold start the introduction of lower viscosity lubricants such as 0W-8 showed higher level of oil control ring-cylinder liner friction in comparison to the 0W-40. The information and experimental facility are of critical use for engine designers when considering the potential contradictory component efficiency behaviour when moving to ultra-low viscosity lubricants.

Development of Prediction Method for Lubricating Oil Behavior around Oil Control Ring with CAE and Experiment Verification

Development of Prediction Method for Lubricating Oil Behavior around Oil Control Ring with CAE and Experiment Verification

Effects of a Cylinder Liner Microstructure on Lubrication Condition of a Twin-Land Oil Control Ring and a Piston Skirt of an Internal Combustion Engine

It is hypothesized that structured sliding-surfaces improve the lubrication condition by forming an oil sump on the sliding surface, redistributing the oil, and trapping wear debris. For these reasons, structured sliding-surfaces have been used as a friction reduction method for a long time. In this work, effects of microstructure laid on the cylinder liner of an internal combustion engine on twin-land oil control ring (TLOCR) and piston skirt lubrication condition were investigated by comparing friction between a conventional fine-honed liner (CFL) and a micro-structured liner with the CFL. The measurements using a floating liner engine showed that the microstructure improved lubrication condition by reducing hydrodynamic friction. On the other hand, it was also observed that the microstructure could result in elevated friction under certain engine operating conditions.Graphical Abstract

Mean pressure of a finite width oil control ring with randomly spaced grooves

The current paper studies the pressure generated between two parallel grooved surfaces, as occurs in the oil control ring in internal combustion engines. It is shown that the pressure generated depends significantly on the position of the groove intersections, and thus that a single calculation cannot describe the pressure generated during a full passage of the ring over the pattern. Furthermore, it is shown that the introduction of a groove distance variation reduces the pressure variation, but does not affect the mean pressure generated.

Cross-hatched groove influence on the load carrying capacity of parallel surfaces with random roughness

For parallel surfaces, i.e. the oil control ring, the micro-geometry completely determines the hydrodynamic lubrication (HL).The cross-hatched grooves provide a certain load carrying capacity (LCC) and the surface (plateau) roughness can be an additional source. This paper extends earlier work to numerically solve the hydrodynamic pressure and LCC of parallel surfaces with random roughness and/or grooves. The influence of the groove spacing, width and depth on the LCC is studied.Results show that the larger the groove spacing, the higher the LCC. Grooves generate a large part of the LCC when the plateau roughness is small. However, for rough surfaces, grooves decrease the LCC and the wider or the deeper the grooves, the larger the decrease of the LCC.

Dimple influence on load carrying capacity of parallel surfaces

In the case of parallel surfaces, such as the oil control ring, no load carrying capacity is generated without texture. A flow conserving multigrid code is used to solve the hydrodynamic lubrication equation described by the Reynolds equation. This code is used to investigate the influence of texture geometry (dimples) and its position along the contact. In particular the behavior of the load carrying capacity according to the texture position on the central line of the contact is studied. To generate positive load carrying capacity, only partial texturing must be used. A significant difference can be observed between inlet texturing and outlet texturing. A multigrid code has been developped that allows a comparison between Dirichlet and periodic results. A comparison with equivalent step bearings is made to analyse the load carrying capacity.

Novel testing methods for screening the tribological performance of ring-liner surfaces

The piston system accounts for about the half of the frictional losses of internal combustion engines and requires special testing methods to understand and improve its function. The most common way to screen the surface performance is to rub ring/liner segments against each other in a reciprocating manner. However, short reciprocating tests have intrinsic low sliding speeds, unable to reach the mixed/hydrodynamic regimes found in the engine, especially at the mid-stroke. This paper presents a rotating test for the oil control ring, which has the largest frictional losses of all other rings. Both reciprocating and rotating tests were conducted using different in-house developed modules and fixtures. Twin land oil control rings against liners with two different finishes commonly used in heavy duty diesel truck engines were tested under similar loads and speeds as in a real engine. Engine oil 5W-30 and room temperature was used for all the tests. Sliding speed, load, friction force and electrical resistance were recorded during the tests. The results show a clear discrimination of the different liner finishes depending on the lubrication regime present.

A comprehensive study of the effects of honing patterns on twin-land oil control rings friction using both a numerical model and a floating liner engine

Engine bores are finished with a multi-stage honing process and the finished surface roughness contributes significantly to the piston ring hydrodynamic pressure generation, especially for twin-land oil control rings whose land profile is parallel to the liner surface. In this paper, five different honing patterns on a cast iron liner and one on a spray-coated aluminum liner are studied with a floating liner engine and numerical models. The liner temperature and engine speed were varied such that all the lubrication regimes, namely boundary, mixed, and fully hydrodynamic, are present. It is found that the models based on deterministic approach with a patch of carefully measured liner roughness can match the trend of the Stribeck curves for different liner finishes observed in the experiment. Furthermore, the results show that the roughness height and structure of the honing affect the twin-land oil control rings lubrication differently. With the same honing structure, although rougher liner experiences mixed and boundary lubrication in larger range of Gumbel–Hersey number, it renders less friction than the smoother ones in the hydrodynamic regime. With the same plateau roughness height, a more continuous plateau can provide more flow resistance and thus generate higher hydrodynamic pressure at the ring–liner interface and less friction.

A Numerical Analysis on the Effect of Several Factors on the Oil Pressure under Oil Control Ring Which Relates to Oil Consumption

A Numerical Analysis on the Effect of Several Factors on the Oil Pressure under Oil Control Ring Which Relates to Oil Consumption

Influence on friction from piston ring design, cylinder liner roughness and lubricant properties

The piston rings are responsible for a large portion of the fuel consumption in heavy duty diesel engines. In this work a high speed component test rig for evaluation of piston ring friction is used. A number of different piston rings and cylinder liners are evaluated based on their friction performance. Shear thinning of typical multi grade oil is investigated by comparing it to single grade oil. Experimental simulation of higher speeds by decreasing the viscosity is evaluated. A method for indication of effects on oil consumption, without combustion, for different oil control rings is presented. Finally, a numerical simulation model for the oil control ring is validated by comparing the friction predicted with the model to the experimental results.

Texture-induced effects causing reduction of friction in mixed lubrication for twin land oil control rings

Piston rings are responsible for a major part of the frictional losses in a heavy-duty diesel engine. Such losses can be reduced by applying texture, such as dimples, on the cylinder liner surface. This paper investigates the effect of such texture on the friction between a land of the oil control ring and a textured cylinder liner via numerical simulation. A simulation model considering inertia and mixed lubrication together with a mass-conserving cavitation model is developed. The model is used to determine the dimple parameters that yield the lowest amount of friction for a specific oil control ring of a heavy-duty diesel engine.