Search Results (72)

Reducing friction in the piston ring–cylinder liner contact is a key area for improving the efficiency of internal combustion engines. While tribological studies commonly focus on the top dead centre region using linear tribometers, the mid-stroke regime—with its higher sliding velocities—remains experimentally inaccessible to most conventional test methods. This study presents a rotating ring-on-liner tribometer that enables investigations at constant relative speed by transitioning the motion from oscillating to rotating. A cylindrical substitution geometry for the piston ring specimen is derived through a coupled elastohydrodynamic and asperity contact simulation approach to reproduce realistic load-sharing behaviour. Experimental results from starved lubrication tests demonstrate stable contact conditions with a low coefficient of variation in wear, confirming good reproducibility. Stepwise performed Stribeck tests at 40 °C and 100 °C reveal characteristic friction–velocity behaviour, including the transition from mixed to hydrodynamic lubrication. Although the test rig’s maximum sliding speed and steady-state thermal conditions differ from fired engine environments, the methodology closes an important gap between low-speed linear tribometers and complex floating-liner systems. The presented approach provides a flexible and robust platform for controlled parametric studies of ring-on-liner contacts under application-relevant lubrication regimes. Full article

High-power clutches operating under high-frequency engagement–disengagement cycles demand piston ring seals with exceptional leakage control and tribological reliability. Conventional architectures often experience lubrication failure and severe adhesive wear during transient pressure fluctuations. This research proposes an autonomous intelligent sealing strategy leveraging fluid pressure-induced morphological evolution. By strategically integrating periodic macroscopic structural relief features on the non-sealing surface, the sealing interface transforms into a micron-scale wavy topography in response to hydraulic loading. This structurally embedded intelligence significantly improves fluid pressure distribution, facilitating a transition toward a more favorable lubrication regime. Furthermore, a “self-healing and positional stagnation” logic is elucidated: upon pressure dissipation, the induced waviness elastically recovers to a planar state to ensure sealing integrity, while the ring maintains its axial position due to the predominant frictional resistance of the secondary seal. This synergistic mechanism effectively precludes deleterious dry friction during the clutch disengagement phase. High-fidelity numerical investigations, benchmarked against established experimental data, identify the rectangular groove configuration as the optimal geometry for maximizing waviness amplitude (≈1.5 µm). This research provides a robust framework for developing responsive, zero-wear intelligent seals in advanced power transmissions. Full article

Some European Heavy Duty (HD) vehicle manufacturers have adopted Open Crankcase Ventilation (OCV) systems to improve reliability and performance. The emission compliance of HD vehicles both during certification and In-Service Conformity (ISC) testing need to also account for the crankcase ventilation. Despite that, the contribution of crankcase emissions to the overall emissions profile of modern trucks remains underexplored. This study experimentally characterizes the crankcase emissions of a Euro VI Step E HD truck equipped with an OCV system under controlled conditions on a chassis dynamometer. Emissions were measured over the World Harmonized Vehicle Cycle (WHVC) and an ISC-compliant driving cycle at two test cell temperatures. The results indicate that crankcase emissions account for up to 4% and 8% of the current regulatory limits for nitrogen oxides (NO_x) and 23 nm solid particle number (SPN₂₃), respectively. The tightening of NO_x limits under Euro 7 regulations would increase these contributions to approximately 11%. SPN₁₀ crankcase emissions were found to be on the order of 10¹¹ (11% of the Euro 7 limit). Real-time SPN₁₀ and SPN₂₃ measurements revealed that the fraction of nanosized particles increases significantly during cold start, suggesting increased oil combustion within the cylinder. These findings highlight the need to refine crankcase emissions measurement procedures within regulatory frameworks. A systematic investigation of measurement setups and ageing effects, taking into account variations in OCV system designs and piston ring wear, is essential to determine whether characterization during certification is sufficient or if ISC testing throughout the vehicle’s useful life will be required. Full article

With the increasing demand for energy conservation and emission reduction in the automotive industry, optimizing the performance of cylinder liner and piston ring pairs in engines has become crucial. Aluminum–silicon alloy cylinder liners, known for their lightweight and excellent thermal conductivity, have emerged as a new trend in cylinder liner materials. Given the relatively moderate hardness of Al-Si alloys, judicious selection of piston rings is imperative to ensure optimal performance. This study investigates the tribological properties of aluminum–silicon alloy cylinder liners paired with CKS and DLC piston rings. The surface morphology and hardness of the test materials were characterized, and reciprocating friction and wear tests were conducted, using a tribometer to simulate operating conditions. The friction coefficient and wear volume were used as indicators to evaluate the tribological properties of the piston rings. The results show that, when the aluminum–silicon alloy cylinder liner was paired with a DLC piston ring, the friction coefficient was 27.82% lower, and the wear volume of the cylinder liner was 83.52% lower, compared to pairing with a CKS piston ring. When paired with a CKS piston ring, wear was exacerbated because silicon particles were easily dislodged to form abrasive particles. This particle detachment is mainly caused by the collision between the fine ceramic particles embedded in the CKS coating and the silicon particles (≤5 μm) uniformly distributed in the Al-Si alloy cylinder liner during the sliding process. The DLC piston ring, containing both sp² and sp³ hybridized carbon–carbon bonds, combined excellent lubrication properties with high hardness, resulting in minimal wear on both the cylinder liner and piston ring. Specifically, the DLC coating has a hardness of 2300 HV_0.3, which is 2.42 times that of the CKS piston ring (950 HV_0.3); the sp³-hybridized carbon in the DLC coating enhances its wear resistance to resist scratching from silicon particles in the cylinder liner, while the sp²-hybridized carbon forms a graphite-like transfer layer at the friction interface to reduce frictional resistance. In conclusion, the aluminum–silicon alloy cylinder liner paired with a DLC piston ring exhibits superior tribological properties. Selecting an appropriate piston ring can significantly enhance the tribological properties of the cylinder liner–piston ring pair, thereby extending the engine’s service life. Full article

Atmospheric plasma spraying was used to create composite coatings employing mixed alloy matrices supplemented with carbon-based solid lubricants as feedstock materials. The current study’s goal was to examine the tribological properties of these coatings and explore the potential benefits of using CNTs as a nano-additive to minimize wear and friction while enhancing lubrication conditions in tribosystems such as piston ring–cylinder liner systems. Pin-on-disk measurements are used to correlate the chemical composition of feedstock materials with the friction coefficient and wear rate during coating operation. The enhanced behavior of the produced coatings is investigated. The anti-wear performance of Co-based cermet and metal alloys coatings, as well as the enhanced lubrication conditions during operation, are shown. In-depth discussion is provided regarding how the features of the feedstock powder affect the quality and performance of the produced coatings. The results showed that coatings based on the CoMo alloy exhibited an increase in wear due to CNT agglomeration. In contrast, CNT addition led to an improvement in bonding strength by up to 33%, a reduction in wear rate by up to 80%, and a decrease in the coefficient of friction from approximately 0.70 to 0.35 in CoNi cermet coatings. These findings demonstrate the role of CNTs in coating performance for demanding tribological applications. Full article

Advanced engineering materials are in high demand for a combination of tailored properties in a single material. Titanium with aluminum alloys is widely used to prepare pistons and knee joints due to its high strength and abundant availability. The primary focus of the study was to utilize an eco-friendly composite material with low cost and a simple production process. Ti–48Al–2Cr–2Nb with molybdenum disulfide was added as reinforcement in varying percentages, fabricated using the squeeze casting production technique. The dry sliding wear test was performed. Adding 4% molybdenum disulfide to Ti–48Al–2Cr–2Nb enhanced its mechanical properties and wear resistance by 57%. Full article

This study presents a comprehensive evaluation of the tribological behavior of cylinder liners and piston rings—key components in internal combustion engines (ICEs). Experiments were conducted using a pin-on-disc wear tester under varying loads (50–100 N) and speeds (175–350 rpm) to determine the coefficient of friction (μ) and wear rate. The selected pin and disc materials represent real engine components to ensure realistic operating conditions. Before and after each experiment, the cylinder liner-piston ring pair was cleaned with acetone to ensure accurate measurement of mass loss. Surface roughness (Ra, Rq, Rz, µm) was assessed using a Mahr M-1 profilometer, and Brinell hardness tests were carried out using a digital optical Brinell hardness testing machine to determine the mechanical properties of the contact surfaces. The results revealed that safflower oil achieved the lowest coefficient of friction at higher speeds, with an 18% reduction compared with conventional 20W-50 engine oil. Camelina oil, camelina biodiesel and safflower biodiesel each exhibited a reduction of approximately 12.5% in friction, highlighting their potential as viable alternatives to petroleum-based lubricants. Full article

With the implementation of the ISO 8217-2024 marine fuel standard, the use of high-concentration biofuels in ships has become viable. However, relatively few studies have been conducted on the effects of biofuels on cylinder lubrication performance in low-speed, two-stroke marine diesel engines. In this study, catering waste oil was blended with 180 cSt low-sulfur fuel oil (LSFO) to prepare biofuels with volume fractions of 24% (B24) and 50% (B50). These biofuels were evaluated in a MAN marine diesel engine under load conditions of 25%, 50%, 75%, and 90%. The experimental results showed that, at the same engine load, the use of B50 biofuel led to lower kinematic viscosity and oxidation degree of the cylinder residual oil, but higher total base number (TBN), nitration level, PQ index, and concentrations of wear elements (Fe, Cu, Cr, Mo). These results indicate that the wear of the cylinder liner–piston ring interface was more severe when using B50 biofuel than when using B24 biofuel. For the same type of fuel, as the engine load increased, the kinematic viscosity and TBN of the residual oil decreased, while the PQ index and the concentrations of Fe, Cu, Cr, and Mo increased, reflecting the aggravated wear severity. Ferrographic analysis further revealed that ferromagnetic wear particles in the oil mainly consisted of normal wear debris. When using B50 biodiesel, a small amount of fatigue wear particles were detected. These findings offer crucial insights for optimizing biofuel utilization and improving cylinder lubrication systems in marine engines. Full article

The lubrication performance of the cylinder liner–piston ring (CLPR) is crucial for the energy efficiency and operating reliability of marine diesel engines. To enhance the boundary lubrication of marine engine oil, a 1,3-diketone fluid HPTD (1-(4-hexylphenyl) tridecane-1,3-dione, HPTD) was introduced as an ash-free friction modifier. Besides that, octadecylamine-functionalized nanocopper particles (ODA-Cu) were also added to the marine oil to improve its anti-wear behavior. Through cylinder-on-disk friction tests, the appropriate contents of HPTD and ODA-Cu were determined, which then formed hybrid additives and modified the engine oil. The tribological performance of the modified oil was analyzed under various normal loads, reciprocating frequencies, and testing temperatures. Based on the synergy of the tribochemical reaction of HPTD and the mending effect of ODA-Cu on the sliding surface, the modified oil not only had lower sulfated ash content but also exhibited superior lubrication performance (i.e., reduced coefficient of friction by 15%, smaller wear track by 43%, and higher maximum non-seizure load by 11%) than the pristine engine oil. The results of this study would be helpful for the design of novel hybrid eco-friendly additives for marine engine oil. Full article

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

Piston ring–cylinder liner is one of the most important friction pairs in internal combustion engines. The surfaces of the piston ring and the cylinder liner are affected by high temperature and high pressure, and the influence mechanism of temperature and pressure on their microscopic morphology parameters is yet to be revealed. In this paper, high temperature friction and wear experiments on the piston ring and cylinder liner are carried out to obtain the microscopic morphology of the cylinder liner and piston ring at different temperatures and pressures, and their changes under different temperatures and pressures are investigated by using two methods, namely, fractal dimension and three-dimensional surface roughness characterization. The results show that, as the temperature increases, the texture patterns on the cylinder liner’s friction surface become simpler, with the fractal dimension showing a decreasing trend while the roughness shows an increasing trend. Compared to the condition at 80 °C, the surface roughness (Sa) of the cylinder liner increased by approximately 58.43% at 190 °C, while that of the piston ring increased by about 96.5%. With increasing pressure, both the fractal dimension and the roughness of the friction surface first decrease and then increase. Full article

High-temperature fretting wear typically occurs on mechanical contact surfaces in high-temperature environments, with displacement amplitudes generally in the micrometer range (≤300 μm), such as the turbine disks and blades in aerospace engines, and the piston rings in automotive engines. The study performed tangential fretting wear tests between superalloy specimens and Si₃N₄ balls under 700 °C to investigate the influence of ground and milled surface morphologies on the high-temperature fretting wear behavior. The experimental results show distinct wear mechanisms for the two surface types: ground specimens exhibit adhesive and oxidative wear, while milled specimens experience fatigue and abrasive wear. Both wear modes intensify with increasing load and fretting frequency. A comprehensive surface morphology characterization method, combining fractal dimension (FD) and surface roughness, is proposed. The study reveals that the roughness parameters Sa and Ra are strongly correlated with the Coefficient of Friction, while FD is strongly correlated with the wear volume. This study provides a novel approach to characterizing the evolution of surface morphology during high-temperature fretting wear. Full article

This experimental study investigates the critical role and impact of additive concentration in enhancing the tribological performance of castor oil as a biolubricant for agricultural tractor engines. Friction and wear are major contributors to reduced engine efficiency, highlighting the need for effective lubrication strategies. While biolubricants like castor oil offer environmental benefits, they often require additives to achieve optimal performance. However, the concentration of these additives is crucial, as an imbalance can negatively impact the lubrication system, leading to a higher coefficient of friction, increased wear, and reduced engine efficiency and lifespan. This study examines the effects of varying concentrations of a mixture of propyl gallate (PG) and ionic liquid (IL) additives on the tribological performance of castor oil. The tribological behaviour of lubricated top compression piston ring and cylinder liner samples was evaluated under simulated engine conditions using a Bruker UMT Tribolab test rig, in accordance with the ASTM G181 standard. The experimental results revealed an influence of additive concentration on the coefficient of friction and wear behaviour. This emphasises the importance of optimising additive formulations to minimise engine wear and friction. Notably, a 0.5% volume concentration of the additive mixture led to a remarkable 34.8% reduction in the average coefficient of friction (COF) and a lower wear rate. 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