Piston Ring Coatings Research Articles

Conjoint impact of modified HHO system, compression ratio variation, and tribological enhancement of steel piston ring substrates on performance and emission characteristics of a spark-ignition engine

In these times of efforts to develop high-efficiency hydrogen-adopted or hydrogen-fueled internal combustion engines (ICEs), and concerns related to electric vehicles such as battery cost, drawbacks in harsh winter climates, low range, etc., it is important to generate original ideas in line with the manufacturing of ICEs with improved efficacy. Accordingly, this study presents a comprehensive experimental investigation to observe the cooperated effects of pulse width modulation (PWM)-controlled hydroxy (HHO) gas introduction and improvement in tribological performance of piston ring-cylinder liner mechanism on performance and emission characteristics of a spark-ignition (SI) engine (co-system). The variation of compression ratio (CR), influence of two electrolyzer types of tube electrolyzer (TE) and plate electrolyzer (PE) for production of HHO gas, and zeta potential (ZP)-based dynamic light scattering (DLS) analysis to specify the optimal catalyst concentration in de-ionized water were also observed. Electron cyclotron resonance-chemical vapor deposition (ECR-CVD) method was utilized to bombard the piston ring substrates with diamond-like carbon (DLC) atoms under high energy plasma to improve the mechanical strength of the friction surface. Using linear tribometer, the uncoated (UPR) and coated piston rings (CPR) underwent friction tests to determine the wear rate (WR), and coefficient of friction (COF) which have substantial contribution to frictional losses. The surfaces of the samples were visualized via scanning electron microscopy (SEM) and atomic force microscopy (AFM) before and after abrasion tests to analyze carbon coating and its effects on tribological performance. The observations depicted that HHO flowrate needs to be varied as the engine load and CR change, and based on these observations, PWM control unit was designed, manufactured and reprogrammed so as to adjust electrical power consumption of HHO system when needed. The aforementioned analyses ensured optimization of the overall system so as to maximize the efficiency of the test engine. The co-system with optimized parameters (CPR + HHO + PWM) yielded an increase in average brake power (Pe) up to 31%, and average reductions in specific fuel consumption (β), carbon monoxide (CO), unburned hydrocarbon (UHC), and nitrogen oxide (NOx) emissions by 17%, 25%, 19%, and 14%, respectively at engine load range from 20% to 100%. It is expected that this study will be a good guide in terms of developing high-efficient ICEs due to promising results provided by the co-system.

Emergence of Coated Piston Ring Scuffing Behavior on an Application-Oriented Tribological Model Test System

A major problem in lubricated piston ring/cylinder liner contact sliding systems is the tribological failure mechanisms known as scuffing. In order to evaluate and better understand this damage phenomenon in these tribological systems, a tilted linear tribometer (TE77) for application-oriented reciprocating model tests was developed and validated with scuffed field engine parts. With precise oil lubrication, original engine parts, such as CKS-coated piston rings (chromium-based coating with included aluminum oxides), original liners and fully formulated lubrications, were tested under conditions similar to the most critical part of the internal combustion engines (ICEs), known as fired top dead center (FTDC). Various in situ measurements during the tests allowed for a detailed investigation of the damage processes (crack transformation) on the tribological components. For the coated piston ring, vertical cracks were attributed to residual stresses, while horizontal cracks resulted from shear stresses. The crack transformation and wear results from other studies were confirmed for the liner. The results from FIB (Focused Ion Beam) cuts, along with EDS and SEM analyses, revealed that Fe (deriving from material transfer) acts as a catalyst on the CKS layer for the tribopads and that zinc sulfides are not present everywhere.

Effect of hydrogen incorporation on the mechanical properties of DLC films deposited by HiPIMS in DOMS mode

The automobile industry has increased its efforts in reducing the emissions of internal combustion engines by improving their efficiency. Decreasing the energy losses by friction in the engines parts is at the core of this attempt. One of the technologies that have been applied in achieving this is the application of carbon coating in engine parts surfaces because of their low friction coefficient characteristics. In this study, DLC films, a specific type of carbon coatings, were deposited using the Deep oscillation magnetron sputtering (DOMS) method, which is a variation of the high-power impulse magnetron sputtering (HiPIMS) method. Those films were deposited with an increasingly higher hydrogen content, and then their mechanical, morphological, and tribological properties were studied. All of this was carried out to verify if the higher hydrogen content is beneficial to use as piston ring coatings in order to decrease friction losses. The variation in the hydrogen content was achieved by increasing the partial pressure of methane inside the deposition chamber during the deposition, which allowed the deposition of films with up to 30 at. % of hydrogen. The variation allowed the depositions of films with a hardness above 10 GPa, a friction coefficient lower than 0.16 (30 % lower when compared to hydrogen-free DLCs), and with specific wear rates in the order of 10−16 mm3/Nm. The hydrogen content also changed the morphology of the films' surface, as well as increasing its deposition rates by 27 %.

A review on preparation process and tribological performance of coatings for internal combustion engine piston ring

Reducing the energy consumption and exhaust emission, and improving the combustion efficiency of internal combustion engine are important for solving the problems of climate change and environmental pollution. The piston ring-liner system is one of the most serious friction pairs in internal combustion engine, accounting for 26% of the total friction loss. Depositing strengthened coatings on the surface of piston rings is an effective method to reduce the friction coefficient and wear rate. This paper reviews the research progress of several representative technologies for preparing coatings, such as electroplating, physical vapor deposition (PVD), thermal spraying and chemical vapor deposition (CVD), and so on. Various coatings, such as Cr-Al2O3 coating prepared by representative electroplating process, CrN and DLC coatings prepared by physical vapor deposition, and Mo-based and C-based coatings prepared by thermal spraying process, are briefly discussed. Furthermore, the positive and negative aspects of commonly used piston ring coatings are compared, and their development trends are summarized.

Coated Piston Ring Pack and Cylinder Liner Elastodynamics in Correlation to Piston Subsystem Elastohydrodynamic: Through FEA Modelling

A finite element model is developed to assess the effects of the TiSiCN thin film coating of the piston ring on the structural strength of the piston subsystem. The complex, cyclically variable forces are considered in load and boundary conditions. The model included combustion dynamics, contact kinetics, piston subsystem primary and secondary motions, and lubricated contact conditions to evaluate the applied forces. A comparative analysis is performed for coated and uncoated cases. Four different crown geometries are tried for selecting the best case of crown design for coated piston subsystem components. The analysis predicts better strength in coated cases compared to uncoated ones. The type-A crown design develops less stress, while the compression ring suffers the most due to elastic deformation and is more prone to fatigue failure.

Combined experimental and simulative approach for friction loss optimization of DLC coated piston rings

Piston rings cause significant friction losses within internal combustion engines. Especially the first compression ring, which is pressed onto the liner by high cylinder pressure, contributes significantly to the total friction loss of the piston assembly. The tribological behavior of the oil scraper ring is mainly related to the pretensioning force and can lead to high losses even at low and idle speed. Due to this, there is always a markable risk of wear for the contact surfaces of the piston rings and the cylinder. “Diamond-like carbon” coatings on the surface of the piston rings can prevent wear and are able to reduce friction in the ring-liner-contact. The purpose of this work was to investigate the tribological benefit of this coating-system on the compression and oil scraper ring. Experimental studies were carried out on a fired single-cylinder engine using the Indicated Instantaneous Mean Effective Pressure-method (IIMEP) for the crank angle-resolved detection of the piston assembly’s friction force. To be able to determine the component-related fractions of the friction loss and to quantify the hydrodynamic and asperity related parts locally and time dependent, an EHD/MBS model of the engine was created in AVL EXCITE and a simulative investigation was performed. This simulation was validated by the experimental work and provided detailed information about the individual contact conditions and gap height of each tribological contact of the piston group. The combined approach of measurement and simulation enabled the prediction of tribological aspects and performance in parameter studies on a virtual engine test bed.

Optimum Selection of Coated Piston Rings and Thrust Bearings in Mixed Lubrication for Different Lubricants Using Machine Learning

The purpose of this study is to build a parametric algorithm combining analytical results and Machine Learning in order to improve the tribological performance of coated piston rings and thrust bearings in mixed lubrication using different synthetic lubricants. The friction models for piston ring conjunction and pivoted pad thrust bearing consider the basic lubrication theory, the detailed contact geometry and the complete lubricant action for a wide range of speeds. The data produced from the analytical solutions are used as input for the training of regression models. The effect of TiN, TiAlN, CrN and DLC coatings on friction coefficient are investigated through multi-variable quadratic regression and support vector machine models. The optimum selection is considered when the minimum friction coefficient is predicted. Smooth TiN2 and TiAlN coatings seem to affect better the ring friction coefficient than rougher steel, TiN1 and CrN coatings using an uncoated or coated Nickel Nanocomposite (NNC) cylinder. Using an NNC cylinder for better durability, the friction coefficients were found to be higher by 31.3−58.8% for all the studied rings due to the rougher surface morphology. On the other hand, the results indicate that pads coated with DLC show lower friction coefficients compared to the common steel and TiAlN, CrN, and TiN applications. The multi-variable second-order polynomial regression models were demonstrated to be 1−6% more accurate than the quadratic support vector machine models in both tribological contacts.

Wear behaviour of ceramic particle reinforced atmospheric plasma spray coatings on the cylinder running surface of internal combustion engines

Atmospheric plasma spray coatings can provide a solution for corrosion and wear resistant cylinder coating surfaces in hybrid powertrains. This article presents experimental results from a model study of metal matrix composite coating samples of chromium steel with varied ceramic content, in order to characterize the effect of hard particles and porous coating structure on friction and wear. Experiments were conducted on a high-frequency reciprocating rig with coated cast-iron cylinder segments and hard chromium coated piston ring segments. Samples were investigated under continuous and scarce lubrication conditions. A ceramic content of 35 wt% was found to be ideal in terms of friction and wear. Coatings with a higher ceramic content exhibited severe abrasive wear, whereas a ceramic content under 35 wt% allowed for increased adhesion between the ring and cylinder surfaces. A detailed investigation of focused ion beam milled sections of the coated cylinder wall segments revealed a stabilizing effect of the ceramic particles, which reduces the delamination of the coating structure.

Modeling and experimental investigation of wear and roughness for honed cylinder liner during running-in process

The tribological property of piston ring and cylinder liner has a great influence on exhaust emissions and service performance of internal combustion engines. To explore the effects of surface topography on tribological property of coated piston ring and honed cylinder liner, the hydrodynamic contact model, asperity contact model and wear model during running-in process are established. Considering the non-Gaussian property of rough surfaces into the contact models, the influences of surface parameters on contact pressure are investigated. Due to the influence of operational condition on lubrication performance, the degradation rate of oil is taken into the wear model. Based on this, the change characteristics of the wear process, coefficient of friction and roughness are investigated. To verify the validity of the proposed models, the tribological test is conducted. The results show that the numerical results are in good agreement with the experimental results, and reasonable surface parameters can improve the anti-wear performance of the system during running-in process.

An Analysis of the Performance Characteristics of Different Cylinder Temperatures for Ni-W and Ni-W-BN(h) Plated Piston Rings in an Air-Cooled Engine

An engine must operate at an appropriate working temperature, the wear resistance of the engine parts must be increased, and frictional loss of energy must be reduced to increase performance and reduce exhaust pollution. This study determines the effect of cylinder temperature and different coatings for piston rings on engine characteristics. Ni-W alloy and Ni-W-BN(h) composite coatings are applied to the compression ring, and the dynamometer test is performed over 50 h using different operating parameters. The experimental data are analyzed by curve fitting for engine performance with cylinder temperature (Tsc) and the concentration of exhaust pollution particles. The experimental results show that a Ni-W alloy plating increases the wear resistance of piston rings. A Ni-W-BN(h) composite coating contains self-lubricating particles, which increases the wear resistance and lubricating properties. In terms of engine performance, Ni-W-BN(h) coated piston rings give the best brake mean effective pressure (BMEP) and fuel conversion efficiency (ηf), and low fuel consumption reduces HC and CO emissions. Therefore, Ni-W-BN(h) is the best coating material for a piston ring.

Development of Thick DLC Coated Piston Ring for Stainless Steel Thermal Spray Coating of Cylinder Bores

Development of Thick DLC Coated Piston Ring for Stainless Steel Thermal Spray Coating of Cylinder Bores

An Experimental Study on Frictional Losses of Coated Piston Rings with Symmetric and Asymmetric Geometry

An Experimental Study on Frictional Losses of Coated Piston Rings with Symmetric and Asymmetric Geometry

Tribological Investigation of Nickel Nanocomposite Coated Piston Rings Reinforced with Multi-Walled Carbon Nanotubes

Tribological Investigation of Nickel Nanocomposite Coated Piston Rings Reinforced with Multi-Walled Carbon Nanotubes

Synergistic effect of surface texturing and coating on the friction between piston ring and cylinder liner contact

It is well-established that the piston ring/cylinder liner (PRCL) contact is the major contributor to friction losses in the internal combustion engine. While numerous studies have evaluated the individual effect of surface engineering techniques like surface texturing, coating, on the PRCL system, however, its combined effect has not been thoroughly explored. In this work, the combined effect of surface coating and texturing on the frictional properties of piston ring/cylinder liner (PRCL) contact in different lubrication regimes has been simulated using a reciprocating tribometer rig. A cylinder liner of cast iron material and three different types of piston ring coatings, namely Diamond-like-carbon (DLC), chrome, and moly-chrome-ceramic (MCC) were used as samples. Under all lubrication regimes, the coated samples with texturing had better frictional performance compared to non-textured coated samples. The maximum friction reduction was observed for textured DLC coated samples under boundary lubrication regime. This behaviour was proposed to be a result of the synergistic effect of graphitisation and texturing.

Wear and corrosion resistance enhancement of chromium surfaces through graphene oxide coating

Corrosion and wear protection of metals are crucial for all industrial applications. Graphene oxide (GO) is a chemically modified form of graphene and is highly promising for corrosion inhibition. Although corrosion protection of metal surfaces by the use of graphene oxide has been well investigated, anti-wear reduction of graphene oxide has not been studied especially under lubricated condition. In this work, Cr coated steel ring was coated with GO by atmospheric pressure chemical vapor deposition that hasn't been reported in the literature yet. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization, immersion tests and the wear behavior of the coatings was investigated under lubricated conditions. Here we show that GO coated piston rings showed excellent corrosion resistance at extreme corrosive media. Our results also show that GO reacts with ZDDP and forms tribofilm that provides additional wear resistance to the ring, which resulted in very effective wear protection because of no wear scar observation on the ring surface.

Investigating the corrosion-fatigue wear on CrN coated piston rings from laboratory wear tests and field trial studies

The interacting mechanisms of corrosion and fatigue wear of the CrN coated piston rings were investigated in two ways: (1) by comparing the laboratory test data to field results, and (2) by simulating the stress distribution and crack origins in the CrN coating using a Finite Element Method (FEM). The surface and interface characterizations confirmed that fatigue wear resulted in cracking and spalling of the CrN coating. At the same time, corrosive wear was promoted by sulfur incursion along boundary defects in the CrN coating. FEM simulations showed that the magnitude of stresses at the interface of Cr particle/CrN matrix was a function of Cr particulate sizes, and they also identified crack initiation sites at rubbing contacts. The dominant factors contributing to the propagation of the surface/subsurface cracking were elucidated. Inherent defects initiated cracks, and the repetitive shear stress coupled with the effects of corrosive species gave rise to an acceleration of crack enlargement and subsequent severe spalling of the CrN coating.

The Effect of Honing Angle and Roughness Height on the Tribological Performance of CuNiCr Iron Liner

This work investigated the effect of honing morphologies of CuNiCr iron liner on its tribological properties sliding against the Cr-Al2O3 coated piston ring. The worn surface morphology and elements distribution as well as the wear behaviors of CuNiCr iron liner were analyzed to explore the influencing of the honing angle and roughness height on the friction and wear resistance. The results show that the optimized honing angle and roughness can improve the tribological performance of the iron liner, and different tribological characteristics are closely related to different roughness parameters. The wear process of the CuNiCr iron liner against Cr-Al2O3 coated piston rings in sequence was platform flattening, plastic flow, growth of the flakes on the platform edge and flakes debonding. For the smooth surface, the plastic deformed flakes were much fewer due to the low height of the platforms, thus the grooves were not fully filled and there was a slight effect of the debonded debris on the friction pair.

Friction Performance of Aluminum-Silicon Alloy Cylinder Liner after Chemical Etching and Laser Finishing

In order to enhance the surface friction performance of the aluminum-silicon (Al-Si) alloy cylinder liner, chemical etching and laser finishing techniques are applied to improve the friction performance. The cylinder liner samples are worn against a Cr-Al2O3 coated piston ring by a reciprocating sliding tribotester. The friction coefficient and weight loss are measured to determine the friction performance; a stress contact model is developed to ascertain the wear mechanism. The results show that the optimal etching time is 2 min for the chemical etching treatment and the optimal laser power is 1000 W for the laser finishing treatment. The chemical etching removes the surface aluminum layer and exposes the silicon on the surface, thereby avoiding metal-to-metal contact. The laser finishing results in the protrusion and rounded edges of the silicon particles, which decreases the stress concentration. The laser finishing results in better friction performance of aluminum-silicon alloy cylinder liner than the chemical etching.

Wear Behavior of CuSn Coated Piston Ring Sliding against Nodular Cast Iron Cylinder Liner under Heavy-Duty Conditions

In order to investigate the friction and wear behavior between the nodular cast iron cylinder liner (Fe) and CuSn coated piston ring under heavy-duty conditions, piston rings with chromium(Cr) coating and CuSn-Cr coating were tested using the piston ring reciprocating liner test rig at the simulated working conditions of 56 MPa, 200 r/min, 190 °C. Compared with the Cr/Fe pair, the CuSn coating consumption of the CuSn-Cr/Fe pair made friction coefficient and cylinder wear loss decrease by 2.8% and 51.5%, respectively. Different size Sn patches worn from the CuSn coated piston ring were embedded into the cylinder liner surface based on the surface topography. This process was shown to reduce the surface roughness of a cylinder liner and form flatter plateau structures. Chemical elements analysis indicated that plateau structures on the cylinder liner surface matched with CuSn-Cr coated ring are helpful to promote the tribo-chemical reaction and generate the reactive products to protect the mutually contacted asperities.

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.