Ring Cylinder Liner Contact Research Articles

A Comprehensive Review on Tribological Behaviour of Hybrid Nanocellulose-CuO as Nanolubricant for Piston Ring Cylinder Liner Application

Friction coefficient and wear rate are crucial performance for the development of nanolubricants, which are of great significance for realizing energy conservation and prolonging service life of mechanical components. Herein, this review systematically describes the progress on nanocellulose (CNC) and Copper (II) oxide (CuO) as effective nanoparticles for developments of nanolubricant as oil additives for improving the anti-friction and wear resistant for piston ring-cylinder liner contact. Additionally, we point out several problems existing in the applications of CuO and CNC additives propose the possible solutions. Finally, the research prospects of CNC-CuO in the field of tribology are prospected.

Scuffing initiation caused by local starvation in a piston ring cylinder liner contact

Scuffing is a localized damage process caused by a sudden failure of the lu- bricating film in a sliding contact. It is associated with an important increase in temperature, friction and vibration. For the piston-ring cylinder-liner (PRCL) contact, it can lead to a complete engine failure. It is shown in this paper, that the temperature gradient generated in the contact induces the thermal Marangoni effect. The latter might then lead to a localized lack of lubricant that can initiate scuffing. On the contrary, the ring displacement along the liner redistributes the oil on the surface. This redistribution helps to avoid starvation hence reducing scuffing initiation risk. Based on the competition occurring between these two effects, a computational model was developed that predicts scuffing appearance in internal combustion engines. The origi- nality of this paper lies in presenting the complementary contribution of the Marangoni phenomenon to the scuffing initiation in the PRCL contact.

Shear-area variation: A mechanism that reduces hydrodynamic friction in macro-textured piston ring liner contacts

Using a reciprocating rig to simulate the piston ring-cylinder liner contact, we show that macro-scale surface texture yields friction reductions in the hydrodynamic regime of up to 35%. Based on these experimental observations, we put forward a new macro-texture induced friction reduction mechanism and validate it through theoretical 1D modelling. This “Shear-Area Variation” mechanism involves macro-texture reducing both the sheared contact area (acting to decrease friction) and hydrodynamic load support/lubricant film thickness (acting to increase shear-rate and hence friction). Provided the oil film is thick enough to prevent asperity contact, the area reduction effect dominates the friction response. This has implications for machine efficiency improvements, as friction is reduced around mid-stroke where sliding speed and energy dissipation is greatest. It also complements the majority of surface texture research which involves micro-scale texture that is only effective at low speeds in the mixed and boundary regimes (around top and bottom- dead centre).

Effect of Dispersant Concentration With Friction Modifiers and Anti-Wear Additives on the Tribofilm Composition and Boundary Friction

Abstract To extend drain intervals and improve efficiency, new engine oils with increased dispersant concentration and reduced viscosity are required. Low viscosity engine oils can increase the prevalence of boundary friction at low temperature and increase its severity at higher temperatures. As a result, combinations of organic and inorganic friction modifiers (FM) will be used to reduce boundary friction across a range of temperatures, also preventing damage to vehicle catalysts. This paper presents an experimental case study of such a new generation of fully formulated engine lubricants with varying concentrations of polyisobutylene succinimide dispersant, organic, and inorganic FM. Representative conditions pertaining to those encountered at the top dead center reversal of the piston compression ring-cylinder liner contact are created, and the generated friction measured through use of a sliding-strip tribometry. Subsequently, X-ray photoelectron spectroscopy (XPS) is used to determine the composition of the formed surface tribofilms in order to explain the observed frictional characteristics. The key interactions and frictional behavior of the dispersant and friction modifiers are highlighted across a range of operating temperatures.

Techniques used to improve the tribological performance of the piston ring-cylinder liner contact

The mechanical assemblies in automotive engines are usually lubricated by a combination of oil and solid lubrication films. Consequently, the significant current challenges for developing the tribological behavior of vehicle engines need the lubricants that conform to different operating conditions by providing mechanisms for reducing friction and wear. This article summarily reviews the techniques used to improve the tribological performance for piston ring-cylinder liner contact and evaluates their effectiveness to provide the most assuring approaches to reduce friction and wear. The objective was to explore the areas where there are openings for further research contributions to achieving an improvement in the piston ring-cylinder contact in automotive engines.

Synthesis of oil-soluble WS2 nanosheets under mild condition and study of their effect on tribological properties of poly-alpha olefin under evaluated temperatures

Abstract A liquid phase method was adopted to encapsulate tungsten disulfide (WS2) nanosheets with oleylamine (OA) at a relatively lower temperature of 200 °C so as to acquire good solubility in organic lubricant base oil. The effect of OA-modified WS2 nanosheets on the tribological properties of poly-alpha olefin (PAO6) in a wide temperature range was examined with a four-ball machine and a UMT TriboLab test rig in a piston ring-cylinder liner contact mode. Results indicate that the OA-modified WS2 nanosheets added in PAO6 oil are able to improve the tribological properties of the lubricant base oil significantly at elevated temperatures; and they are advantageous over zinc dialkyldithiophosphates in improving the anti-wear ability of PAO6 from room temperature to 300 °C.

A quantitative wear measurement method on production engine parts: Effect of DLC thin films on wear

The automotive industry is facing worldwide pressure to reduce carbon emission to meet the Paris Accord target of 2 °C increase in global average temperature by the end of the century. One way to reduce carbon emission is to improve fuel economy of cars and trucks. Recent emergence of ultralow viscosity lubricants has shown significant fuel economy benefits. However, the resulting low oil film may cause increased surface contacts and could lead to increased wear. The ability to measure the initiation phase of wear before it accelerates towards failure is an important issue today. Quantitative measurement of wear in engine parts has always been a challenge. In today’s fuel efficient engines, coatings increasingly being introduced into engine component manufacturing, wear metrology of small amount of wear spread over a large area of rough surfaces presents even a greater challenge.This paper describes the development of a quantitative measurement technique to measure mild wear over a relatively large area of rough production engine surfaces. One of the critical engine sliding components is the piston ring vs cross-hatched cylinder liner contact interface. The availability of a quantitative wear measurement technique would allow comparison of various materials, including coated rings, and liner surface treatments. In this study, production rings and liners were obtained from cooperative engine manufacturers under non-disclosure agreements. A reciprocating ring-liner test rig was used to conduct the wear tests, using a newly developed cyclic wear test procedure, sequence of speed and load cycles were used for simulating sliding motions. Mini-cycles (a constant speed with varying loads from 160 N to 240 N) at 120 °C, and at 6 Hz reciprocating frequency were used. An experimental 0 W-16 lubricant, which has gone through engine testing, was used in the wear tests. A dual white light interferometric microscope (Z resolution 1 Å) was used to measure the liner wear. An analytical balance with 1 µg resolution was used to measure the ring segment weight loss. After the wear measurement procedure was established, diamond-like carbon (DLC) coated rings were also used to assess the effect of the DLC on the wear, and the measurement technique. A digital 3D surface topography subtraction technique was successfully developed to measure quantitative wear of the liner. This technique can be used for other wearing engine parts.

Tribological Investigations of Silicon Nitride Lubricated by Ionic Liquid Aqueous Solutions

Water-lubricated ceramic components are promising material combinations for tribological applications because they are wear resistant and can exhibit low coefficients of friction under different loads. The aim of the work was to show in model tribological experiments with silicon nitride that the lubricating properties of water can be improved by adding water-soluble ionic liquids (ILs). The geometry used and the experimental parameters were selected to approximately simulate a piston ring–cylinder liner contact. We found that the addition of 1% IL tributyl methyl phosphonium acetate [P4441][OAc] leads to a reduction of the maximum friction work by 58% compared to pure water lubrication and even by 96% compared to oil-lubricated steel. It was shown that suitable running-in conditions and sufficient cooling by the lubricant at an early stage are important prerequisites for achieving low friction and wear values. In addition, the chemical interaction of water and IL with silicon nitride strongly affects the tribological behavior. As increasing demands on sustainability (green tribology) become more important due to environmental aspects, this work provides important insights for the development of novel water-based lubricant systems.

Synergistic effects of electroless piston ring coatings and nano-additives in oil on the friction and wear of a piston ring/cylinder liner pair

To enhance the tribological performance of piston ring-cylinder liner pair in engines, Ni-P-TiN coated piston rings were prepared by electroless plating technology, and novel Fe3O4@MoS2 nanocomposites were used as lubricating additives in oil. The tribological behavior of the coated friction pairs was evaluated on a multifunctional piston ring-cylinder liner tribometer. The results show that the concentration of TiN nanoparticles in the coatings has an important effect on the tribological performances. The coated piston ring-cylinder liner contact presented a mild abrasive wear with the concentration of TiN nanoparticles at 1.5 g/L. The coated piston rings did not increase the wear loss the cylinder liner due to the lubricating roles of TiN nanoparticles and the formation of transfer layer. The friction coefficient and wear loss of the Ni-P-1.5TiN coatings reduced by 23.8 ± 3.1 wt% and 64.3 ± 1.8 wt%, respectively, comparing to that of the Ni-P coating. Compared with nano-MoS2 and nano-Fe3O4, the Fe3O4@MoS2 nanocomposites as oil additives have a better effect on reducing the friction and wear of the Ni-P-TiN composite coating, mainly due to the synergistic effects of the coatings and the nanocomposite additives.

Optimisation of the piston compression ring for improved energy efficiency of high performance race engines

The primary function of the piston compression ring is to seal the combustion chamber from the bottom end of the engine. As a result, its conformance to the cylinder liner surface is of prime importance. This close-contact contiguity results in increased friction, making this contact conjunction responsible for a significant proportion of energy losses. The frictional losses can be as much as 2–6% of the expended fuel energy, which is quite significant for such a diminutive contact. Under these conditions, the geometrical profile, the surface topography and the inertial properties of the ring assume significant importance. The paper presents an integrated mixed-hydrodynamic analysis of the compression ring–cylinder liner contact with multi-parameter optimisation, based on the use of a genetic algorithm. The multi-objective functionality includes minimisation of the parasitic energy loss, reduction in the incidence of asperity level interactions as well as minimisation of the ring mass. Both cold running engine conditions and hot running engine conditions in line with the New European Drive Cycle were considered. Hitherto, such an approach has not been reported in the literature.

A combined analytical‐experimental investigation of friction in cylinder liner inserts under mixed and boundary regimes of lubrication

AbstractIt is necessary to develop an analytical solution in order to combine predictions with measured tribological parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time‐efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel‐Silicon Carbide wear‐resistant coating of choice in high performance motorsport. © 2017 The Authors Lubrication Science Published by John Wiley & Sons Ltd.

Computational fluid dynamics analysis of top compression ring in mixed lubrication

The top compression ring design of an internal combustion engine has an impact on ring in-plane motion and its lubrication conditions at the ring-cylinder liner contact. In this paper, the geometrical dimensions of the top compression piston ring-cylinder system were obtained from an actual four-stroke motorbike engine. The top ring tribological behaviour was characterized by a Computational Fluid Dynamics (CFD) simulation including the effects of asperity contact. Based on the numerical solution of the Navier–Stokes equations and taking into account realistic engine running conditions, the effect of the in-plane top ring motion in quasi-static equilibrium was determined. The simulation model was validated by the numerical and experimental results of similar investigations of other researchers. Good predictions were achieved by solving the Navier-Stokes equations because the pressure gradient into the lubricant film was accounted for. The effects of ring curvature at the ends of the stroke were studied. The results show that a flatter ring profile has a sufficient minimum lubricant thickness at reversal points, showing reasonably lower boundary friction than that of the higher curvature. Higher heights of the curvature profile promote significantly mixed lubrication, in which the power losses and the burning of excess lubricating oil are increased. The proposed simulation model can be expanded to any set of compression rings where a minimum simulation time is required.

Molecular dynamics investigation of a model ionic liquid lubricant for automotive applications

In the current work we present a new modelling approach for simulating meso–scopic phenomena related to lubrication of the piston ring–cylinder liner contact. Our geometry allows a variable confinement gap and a varying amount of lubricant in the gap, while avoiding the squeeze-out of the lubricant into vacuum. We have implemented a coarse grain molecular dynamics description of an ionic liquid as a lubricant which can expand into lateral reservoirs. The results have revealed two regimes of lubrication, an elasto-hydrodynamic one under low loads and one with low, velocity-independent specific friction, under high loads. The observed steep rise of normal forces at small plate-to-plate distances is an interesting behaviour that could potentially be exploited for preventing solid–solid contact and wear.

Load carrying capacity and friction of an inclined parabolic-flat piston ring

Reducing the fuel consumption of a combustion engine has been an important design issue. Engine friction has to be reduced and the piston ring-cylinder liner contact is a major source of friction. The current work analyses the friction and load carrying capacity of an inclined parabolic-flat piston ring. This relatively simple geometry permits an analytical solution of the pressure distribution, the load carrying capacity and the friction. The friction coefficient is given as a function of twist angle, flat width and total width. The analytical expressions allow many thousands of calculations per second.

Component test for simulation of piston ring – Cylinder liner friction at realistic speeds

The piston ring cylinder liner contact is a large contributor to mechanical friction losses in internal combustion engines. It is therefore important to have methods and tools available for investigations of these frictional losses. This paper describes the design of a novel component test rig which is developed to be run at high speeds with unmodified production piston rings and cylinder liners from heavy duty diesel engines. A simplified floating liner method is used and the test equipment is developed to fill the gap in between a full floating liner engine and typical component bench test equipment. The functionality and repeatability of the test are investigated and an unexpected behaviour of the twin land oil control ring is found.

A robust piston ring lubrication solver: Influence of liner groove shape, depth and density

A multigrid code using Alcouffe׳s [1] ideas has been written to solve the hydrodynamic lubrication equation for the piston ring–cylinder liner contact with a textured liner. The new program shows good convergence, even for deep grooves. Results are compared with a simplified 1D analytic model proposed by Biboulet [2]. Then a 2D analytic model of cross hatched grooves with a small angle is studied and compared with the 1D analytic model.

An experimental and numerical investigation of frictional losses and film thickness for four cylinder liner variants for a heavy duty diesel engine

The piston ring pack is the single greatest contributor to mechanical losses in a heavy duty diesel engine, accounting for 1.1–6.8% of the total losses. Therefore, the piston ring-cylinder liner contact is potentially the most rewarding area to study when attempting to reduce mechanical losses in a heavy duty diesel engine. In this work, four different heavy duty diesel engine cylinder liner variants have been tested to evaluate the lubricating conditions that occur when a section of top compression ring is reciprocated against them in a lubricated environment. Two of the cylinder liners were traditional grey cast iron and plateau honed with different honing angles, one had ANS Triboconditioning® applied and the last was plasma sprayed with a stainless steel and ceramic coating, then honed. An experimental test rig was used where friction and film thickness was recorded, by means of an ultrasonic technique. A numerical model was also developed to calculate the friction and film thickness. Comparisons are made between the simulation and experiment, and the four cylinder liner variants are also evaluated. It was found that both simulation and experiment could differentiate between all surfaces and the results from the model and experiment also correlated well with each other. A lower plateau average surface roughness, as exhibited by the ANS Triboconditioning® and plasma liners, led to a significant reduction in friction.

Experimental and numerical investigations of oil film formation and friction in a piston ring–liner contact

The piston ring–cylinder liner contact is a major source of the total parasitic losses in an internal combustion engine. The lubrication process of this contact highly influences the amount of friction, oil consumption and wear that occurs. In this work, a reciprocating test rig combined with an ultrasonic film thickness measurement system was developed and then used for tribological investigation of the piston ring–cylinder liner contact under idealised cold conditions. A special piston ring and cylinder liner holder were designed and five sensors were glued on to the back side of the liner specimen. Ultrasonic reflections captured by the sensors, used to obtain the film thickness, and friction were continuously recorded as the piston ring section reciprocated over the liner. Several experiments were performed at different speed and load conditions. Furthermore, a numerical model has been developed to predict film thickness and friction in all lubrication regimes. The experimentally measured film thickness and friction were compared with the output from the numerical model and good correlation was found. The parameters affecting the accuracy of the ultrasound measurements and numerical simulations of film thickness and friction are then discussed.

A semi-deterministic texture-roughness model of the piston ring–cylinder liner contact

Many simulations already exist to model the piston ring–cylinder liner contact; however, very few models have been used to investigate the optimum surface texture. An axi-symmetric, time-dependent two-dimensional semi-deterministic texture-roughness model of the piston ring to cylinder liner contact with periodic boundary conditions and mass preserving global cavitation has been developed. The cylinder liner texture, generated by honing, was considered deterministically on the global scale, after an investigation comparing deterministic and homogenized solutions. The surface texture of a real cylinder liner was measured with white light interferometry and an algorithm developed to generate an artificial periodic texture representative of the real surface. The effect of cylinder liner plateau roughness has been incorporated on the local scale by homogenization of the Reynolds equation and calculation of flow factors from real surface topography. Using the homogenization technique to incorporate the effect of surface roughness leads to a more efficient solution than mesh refinement of the deterministic problem as the roughness does not need to be resolved on the global solution domain, allowing for significantly less degrees of freedom in the global problem. The lubricant boundary pressures have been calculated using results from a numerical ring-pack model and the lubricant viscosity has been adjusted based on the cylinder liner wall temperature. It was found from the result of a comparison between deterministic and homogenized solutions that surface texture should be modelled on the global and not on the averaged roughness scale as is the case with many previous investigations.