Search Results (41)

The use of combustion engines on agricultural vehicles will persist much longer than on-road vehicles. Introducing new technologies in agricultural engines is crucial to mitigating emissions while accounting for customer cost-sensitivity, harsh operation conditions, and typically sub-optimal maintenance. This work describes the use of CrN and tetrahedral amorphous carbon (ta-C) DLC-coated rings in small agricultural diesel engines. Compared with the gas nitride rings, the CrN and the ta-C DLC coatings exhibited, respectively, 74% and 86% lower wear in rig tests. The DLC also presented a very low coefficient of friction and high resistance to scuffing. A similar wear trend was observed on durability engine tests, where the CrN top ring showed an 80% lower wear rate than the GNS used in a similar engine. Wear on the DLC oil ring was below the measurement capability. Liner radial wear was measured on the piston ring reversal points in four angular positions, and except for one position, was lower than 3 µm. At the end of the test, engine performance and emissions are nearly identical to those at the test’s start, demonstrating that the use of advanced tribological solutions can significantly contribute to emissions mitigation in agricultural engines. Full article

In this work, 1,3-diketone synthesized via the Claisen condensation method and nano-copper particles modified by the Brust–Schiffrin method were added into a commercial marine medium-speed diesel engine cylinder piston oil to evaluate their effects on boundary lubrication performance. Friction and wear tests conducted on CKS-coated piston ring and cast-iron cylinder liner samples demonstrated significant reductions in both friction and wear with the addition of 1,3-diketone and nano-copper particles. Compared to the original oil without additives, the friction force was reduced by up to 16.7%, while the wear of the piston ring and cylinder liner was decreased by up to 21.6% and 15.1% at 150 °C, respectively. A worn surface analysis indicated that the addition of 1,3-diketone and functionalized nano-copper particles influenced the depolymerization and tribo-chemical reactions of the anti-wear additive ZDDP (zinc dialkyldithiophosphate) in the original engine oil. This modification enhanced the oil’s anti-friction and anti-wear properties, offering valuable insights into the development of eco-friendly lubricants for energy-efficient systems. Full article

Friction and wear reduction in internal combustion engines are crucial for improving efficiency and durability. This study investigates the effect of microtextured surfaces on friction power loss in an engine’s piston ring-cylinder system. A numerical analysis was conducted on piston rings equipped with dimple-shaped microtextures using AVL Excite Piston & Rings, modelling a hard chromium-coated piston ring and a cast iron cylinder. The goal was to determine the optimal surface texture parameters that minimize friction power loss under typical urban driving conditions with SAE 0W-30 oil. A two-step Design of Experiments (DoE) approach was employed, where the first step involved mapping the effects of texture parameters, i.e., dimple depth (A = 0.5, 1, 1.5 µm), dimple distance (B = 120, 160, 240 µm), and dimple diameter (C = 50, 60, 70 µm), to identify influential factors. The second step aimed at locating a parameter configuration with minimal friction power loss. The results demonstrated that the optimized texture parameters can significantly reduce friction power loss. The lowest friction power loss of 8.96 W was achieved with a dimple depth of 2 µm, distance of 80 µm, and diameter of 60 µm, which contributed to an 8.3% improvement over the reference surface. The model built to describe the investigated texturing approach exhibited a strong correlation with an R² value of 0.93, and the deviation between predicted and measured values was below 1%. Future work will involve tribometer tests to experimentally validate the optimized parameters and confirm the simulation results. Full article

With the global shift in energy structure and the advancement of the “double carbon” strategy, methanol has gained attention as a clean low-carbon fuel in the engine sector. However, the corrosion–wear coupling failure caused by acidic byproducts, such as methanoic acid and formaldehyde, generated during combustion severely limits the durability of methanol engines. In this study, we employed a systematic approach combining the construction of a corrosion liquid concentration gradient experiment with a full-load and full-speed bench test to elucidate the synergistic corrosion–wear mechanism of core friction pairs (cylinder liner, piston, and piston ring) in methanol-fueled engines. The experiment employed corrosion-resistant gray cast iron (CRGCI), high chromium cast iron (HCCI), and nodular cast iron (NCI) cylinder liners, along with F38MnVS steel and ZL109 aluminum alloy pistons. Piston rings with DLC, PVD, and CKS coatings were also tested. Corrosion kinetic analysis was conducted in a formaldehyde/methanoic acid gradient corrosion solution, with a concentration range of 0.5–2.5% for formaldehyde and 0.01–0.10% for methanoic acid, simulating the combustion products of methanol. The results showed that the corrosion depth of CRGCI was the lowest in low-concentration corrosion solutions, measuring 0.042 and 0.055 μm. The presence of microalloyed Cr/Sn/Cu within its pearlite matrix, along with the directional distribution of flake graphite, effectively inhibited the micro-cell effect. In high-concentration corrosion solutions (#3), HCCI reduced the corrosion depth by 60.7%, resulting in a measurement of 0.232 μm, attributed to the dynamic reconstruction of the Cr₂O₃-Fe₂O₃ composite passive film. Conversely, galvanic action between spherical graphite and the surrounding matrix caused significant corrosion in NCI, with a depth reaching 1.241 μm. The DLC piston coating obstructed the permeation pathway of formate ions due to its amorphous carbon structure. In corrosion solution #3, the recorded weight loss was 0.982 mg, which accounted for only 11.7% of the weight loss observed with the CKS piston coating. Following a 1500 h bench test, the combination of the HCCI cylinder liner and DLC-coated piston ring significantly reduced the wear depth. The average wear amounts at the top and bottom dead centers were 5.537 and 1.337 μm, respectively, representing a reduction of 67.7% compared with CRGCI, where the wear amounts were 17.152 and 4.244 μm. This research confirmed that the HCCI ferrite–Cr carbide matrix eliminated electrochemical heterogeneity, while the DLC piston coating inhibited abrasive wear. Together, these components reduced the wear amount at the top dead center on the push side by 80.1%. Furthermore, mismatches between the thermal expansion coefficients of the F38MnVS steel piston (12–14 × 10⁻⁶/°C) and gray cast iron (11 × 10⁻⁶/°C) resulted in a tolerance exceeding 0.105 mm in the cylinder fitting gap after 3500 h of testing. Notably, the combination of a HCCI matrix and DLC coating successfully maintained the gap within the required range of 50–95 μm. Full article

This study evaluates the tribological characteristics of quasi-monolithic engine cylinder coatings and piston rings using a custom-built linear reciprocating tribometer. The coatings were deposited on an Al-Si alloy cylinder bore using the Plasma Transfer Wire Arc (PTWA) and Electrolytic Jet Plasma Oxidation (EJPO) processes. The coatings’ tribological performances were investigated in the boundary lubrication regime. The performance of conventional chrome-coated cast iron piston rings was tested and compared to that of EJPO- and PTWA-coated engine cylinder samples that were extracted from a cast Al-Si engine block. Scanning electron microscopy and profilometry were used to compare the evolution of wear and the prevalent wear mechanism. This paper also presents the verification and repeatability analysis of a custom-built tribometer against a standard industry-calibrated tribometer. The wear test results showed that the EJPO coating had 0.05% to 10.35% lower wear rates than its PTWA counterpart throughout a wide range of loading conditions and sliding distances. The variation in the counter-face behavior is likely due to the different surface topographic parameters such as skewness, kurtosis, and porosity. Full article

At present, the improvement of anti-wear performance of piston rings remains a challenge. In this article, Ni-SiC composite coatings fabricated at 3, 9, and 15 g/L SiC were denoted as NSc-3, NSc-9, and NSc-15 coatings. Meanwhile, the influence of SiC concentration on the surface morphology, phase structure, microhardness, and anti-wear performance of electrodeposited Ni-SiC composite coatings were investigated utilizing scanning electron microscopy, X-ray diffraction, a microhardness tester, and a friction–wear tester, respectively. The SEM images presented NSc-9 coatings with a compact, flat, or cauliflower-like surface morphology. The cross-sectional morphology and EDS results showed that the Si and Ni elements were uniformly distributed in the NSc-9 coatings with dense and flat microstructures. Moreover, the average grain size of the NSc-9 coatings was only 429 nm. Furthermore, the microhardness and indentation path of the NSc-9 coatings were 672 Hv and 13.7 μm, respectively. Also, the average friction coefficient and worn weight loss of the NSc-9 coatings were 0.46 and 29.5 mg, respectively, which were lower than those of the NSc-3 and NSc-15 coatings. In addition, a few shallow scratches emerged on the worn surfaces of the NSc-9 coatings, demonstrating their outstanding anti-wear performance when compared to the NSc-3 and NSc-15 coatings. Full article

With the marine industry’s demands for carbon reduction and increased reliability, the friction and wear performance of marine engines is becoming increasingly important. MAX phase materials show great potential in marine engine tribopair materials due to their unique microstructure and performance. The typical MAX phase material Ti₃AlC₂ was combined with MoDTC and added to the lubricant containing ZDDP additive for the tribopair composed of chromium-based ceramic composite coated steel (CKS) piston rings and cast iron cylinder liners under impact-sliding conditions. Compared to Ti₃AlC₂ alone, the friction coefficient and wear depth of the designed composite additive MoDTC/Ti₃AlC₂ were reduced by 36.9% and 41.4%, respectively. The worn surface lubricated with the Ti₃AlC₂/MoDTC composite additive showed fewer scratches with significantly less plastic deformation and clearer honing grooves. The multi-component tribofilm containing FeS, MoS₂, MoO₃, ZnO, TiO₂, Al2O₃, unoxidised particles, short-chain phosphates, and some ZnS was present on the worn cylinder liner surface. The synergistic effect of Ti₃AlC₂, MoDTC and ZDDP additives in the lubricant can isolate the mutual contact, generate a solid tribofilm and reduce the scratching. This can provide some guidance for the development of high-performance lubricant additives under impact-sliding conditions. Full article

Axial piston pumps with compact structures and high efficiency are widely used in construction machinery. The efficiency and lifetime strongly depend on the tribological performance of the pump’s valve plate pair. To enhance the tribological performance of the valve plate pair, surface textures, and H-DLC coatings were fabricated to modify the CuAl10Fe5Ni5 surfaces. The influences of elliptic textures of different sizes and textured H-DLC coatings on the surface friction and wear properties of the valve plate surface under oil lubrication were evaluated using a ring-on-disk tribometer. The results reveal that the friction and wear properties of the CuAl10Fe5Ni5 surfaces are significantly enhanced by elliptic textures, and the friction coefficient and wear rate of textured CuAl10Fe5Ni5 with E90 are maximally decreased by 95% and 87%, respectively. Compared with the surface textures and H-DLC coatings, the textured H-DLC coating has the greatest ability to reduce wear and adhesion. The wear rate of the textured H-DLC coating is further reduced by 98%. This improvement can be explained by the synergistic effect of the elliptic textures and H-DLC coatings, which are attributed to the reduced contact area, debris capture, and secondary lubrication of the elliptic textures, and increased surface hardness. Full article

This article compares the tribological performance of coatings produced by PVD sputtering. Transition metal dichalcogenide (TMD) coatings doped with carbon (WSC and MoSeC) and nitrogen (WSN and MoSeN) and a conventional diamond-like carbon (DLC) coating are compared. The tribological evaluation was oriented towards the use of coatings on piston rings. Block-on-ring tests in a condition lubricated with an additive-free polyalphaolefin (PAO 8) and at temperatures of 30, 60, and 100 °C were carried out to evaluate the coatings in boundary lubrication conditions. A load scanner test was used to evaluate dry friction and scuffing propensity. In addition to WSN, all other TMD coatings (WSC, MoSeC, and MoSeN) exhibited lower friction than DLC in dry and lubricated conditions. The study reveals that WSC, among TMD coatings, offers promising results, with significantly lower friction levels than DLC, while demonstrating reduced wear and a lower risk of metal adhesion. These findings suggest that WSC may be a viable alternative to DLC in piston rings, with potential benefits for reducing fuel consumption and increasing engine durability. Full article

This work focuses on the evolution of lubrication wedge shaping in internal combustion piston engines, taking into account liquid microflows on curved surfaces and coating microgeometries. It introduces a new approach to the analysis of friction losses by simulating the microflow of lubricating oil between the surfaces of piston rings cooperating with the cylinder surface. The models used take into account three types of microgeometry and material expansion. Key results indicate that microirregularities with a stereometry of 0.1–0.2 µm significantly influence the distribution of oil film thickness in the phase of maximum working pressure, which is critical for the functioning of the seal ring. The innovation of the work consists of demonstrating that, despite small changes in the friction force and power in the piston rings, changes in the minimum values of the oil film thickness are significant. The work highlights the failure to take into account microgeometry parameters in friction models, which leads to significant errors in the simulation results, especially in terms of oil film continuity and the contribution of mixed friction. The simulations also indicate that advanced geometric models with high mesh resolution are necessary only for the assessment of changes in oil film thickness during the highest pressure increase in the combustion chamber and taking into account various mixed friction conditions. The results suggest significant progress in engine design and performance, confirming the importance of advanced fluid and mixed friction models in piston engine lubrication research. Full article

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. Full article

Internal combustion engines, during their operation, subject the piston to high-temperature and high-pressure conditions, requiring it to endure intense, continuous reciprocating motion. This strenuous process leads to significant wear and tear. Among the engine’s crucial components, the piston ring plays a pivotal role but is particularly susceptible to wear. Therefore, extensive research has been devoted to investigating the wear of piston rings, a critical sealing component within internal combustion engines. To address the high cost of existing coating methods, which hinders widespread application, we propose a bionic design approach inspired by groove structures observed on earthworm bodies, aimed at enhancing the wear resistance of piston rings. Bionic piston rings featuring optimally designed groove structures inspired by the earthworm’s anatomy were designed. These rings exhibited varying groove depths (1 mm, 2 mm, and 3 mm), groove widths (0.1 mm, 0.3 mm, and 0.5 mm), and groove spacings (0.1 mm, 0.2 mm, and 0.3 mm). We conducted thermal–structural coupling analyses on both standard piston rings and these bionic counterparts. The results revealed that the maximum stress was concentrated at the first piston ring, precisely at the opposing region of the end gap. Thus, the initial piston ring endured the primary frictional losses. Moreover, a comparison of stress levels between bionic rings and the standard ring revealed that the bionic groove structure substantially reduced stress and minimized stress concentration, thus enhancing wear resistance. Groove width had the most notable influence on wear performance, followed by groove depth and groove spacing. Optimal wear resistance was achieved when the groove depth was 3 mm, groove width was 0.1 mm, and groove spacing was 0.1 mm. Subsequently, we constructed a piston ring friction test bench to validate the wear resistance of the most effective piston ring. The results indicated that the wear resistance of the bionic piston ring exceeded that of the standard piston ring by up to 19.627%. Therefore, incorporating a bionic groove structure within the piston ring can effectively reduce surface friction and enhance wear resistance. This, in turn, can enhance the operational lifespan of internal combustion engines under favorable working conditions. Full article

In internal combustion piston engines, the formation of an oil film is completely different from that seen in industrial machines. The molecular adhesion force at the interface between the surface coating of engine parts and the lubricating oil determines the load-carrying capacity and the ability to form a lubricated film. The geometry of the lubricating wedge between the surfaces of the piston rings and the cylinder wall is created by the thickness of the oil film and the height of the ring’s coverage with lubricating oil. This condition is affected by many of the parameters that characterize the engine’s operation and the physical and chemical parameters of the coatings used for the cooperating pairs. For lubricant particles that reach energies that are higher than the potential energy barrier regarding adhesive attraction at the interface, slippage occurs. Therefore, the value of the contact angle of the liquid on the surface of the coating depends on the value of the intermolecular force of attraction. According to the current author, there is a strong relationship between the contact angle and the lubrication effect. The paper shows that the surface potential energy barrier is a function of the contact angle and contact angle hysteresis (CAH). The innovation of the current work consists in examining the contact angle and CAH under the conditions of thin layers of lubricating oil, in cooperation with hydrophilic and hydrophobic coatings. The thickness of the lubricant film was measured under various speed and load conditions, using optical interferometry. The study shows that CAH is a better interfacial parameter for correlation with the effect of hydrodynamic lubrication. This paper presents the mathematical relationships relating to a piston engine, various coatings, and lubricants. Full article

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. Full article

The materials used for the piston cylinders of automobile engines, or the ring and tappets of various mechanical components, are continuously experiencing lubricated sliding motions. These surfaces are prone to damage due to the various tribological aspects of friction and wear. Hence, enhancing their surface properties would contribute to increasing their life and saving energy and resources. For many decades surface texturing and surface coating technology have been studied to improve the surface tribological behaviours of the materials. In the present study, the steel surface was textured with electrochemical processing (ECP) and post-coating with transition metal dichalcogenides (TMD) using a molybdenum-selenium-carbon (MoSeC) film. A comparative study was conducted to investigate the synergistic effect of surface texturing and coating to improve frictional properties on the steel surface. The block-on-ring experiments were performed under lubricated conditions to understand the improvement of COF at different lubrication regimes. It has been seen that the MoSeC-coated circular patterns exhibited improvements in the frictional properties at all the lubricated conditions if compared with smooth surfaces. Full article