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This paper presents an experimental study into the flow behaviour of lubricant in a reciprocating contact simulating a piston ring–cylinder liner pair. The aim was to understand the effects of cavitation, starvation and surface texture, as well as the interaction between these, in order to improve automotive engine performance. A custom-built test rig was used, in which a section of piston ring is loaded against a reciprocating, laser-textured, fused silica pad representing the liner. A fluorescence microscope focusses through the silica specimen onto the contact in order to image the distribution of dyed oil. Tests were performed using a range of texture geometries and orientations, under starved and fully-flooded lubrication conditions, with measurements being compared against those from a non-textured reference. Under limited oil supply conditions, the non-textured reciprocating contact sweeps oil towards the reversal points (TDC and BDC), leading to starvation and increased friction. This issue is alleviated by the presence of surface texturing, with each pocket transferring oil from the inlet to the outlet of the contact as it passes; the result being 33% lower friction and oil distributed evenly over the liner surface. Even under fully flooded conditions, starvation is shown to occur following each reversal, as the change in sliding direction causes the cavitated outlet to become the oil-deprived inlet. This proof of cavitation-reversal-starvation, which occurs for up to the first 5% of the stroke length, depending on the lubricant’s viscosity, corresponds to regions of high wear, measured in this study and on actual cylinder liners reported in the literature. This process is also counteracted by the presence of surface texture, with each pocket depositing oil into the cavitated region prior to reversal. Fluorescence data also provides insights into other mechanisms with which different textures geometries control friction. Grooves oriented parallel to sliding direction increase friction as they appear to connect the high pressure inlet with the low pressure outlet, leading to oil film collapse. Grooves oriented transverse to sliding direction produce localised cavitation inside each pocket, which supports the theory that texture draws lubricant into the contact through the ‘inlet suction’ mechanism. These findings can aid texture design by showing how pockets can be used in practice to simultaneously control oil consumption, and reduce friction and wear along the stroke. It should be noted that the lubricant transport mechanisms described above should also result from other types of depressions, such those produced by porous coatings (provided they are smaller than the contact area).

This paper presents a comparison between the results from numerical modelling and experiments to shed light on the mechanisms by which surface texture can reduce friction when applied to an automotive cylinder liner. In this configuration, textured features move relative to the piston-liner conjunction and to account for this our approach is to focus on the transient friction response to individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is based on the averaged Reynolds’ equation with the Patir & Cheng's flow factors and the p-θ Elrod-Adams mass-conserving cavitation model. The contact pressures that arise from the asperity interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp method. The experimental data is produced using a pin-on-disc set up, in which laser textured pockets have been applied to the disc specimen. Under certain conditions in the mixed and boundary lubrication regimes, both model and experimental results show i ) an increase in friction as the pocket enters the contact, followed by ii ) a sharp decrease as the pocket leaves the contact, and then iii ) a gradual decay back to the pre-entrainment value. From the evidence obtained for the first time from the proposed combined modelling and experimental investigation conducted under carefully controlled conditions, we suggest that these three stages occur due to the following mechanisms: i ) a reduction in fluid pressure due to the increased inlet gap, ii ) inlet suction as the cavitated fluid within the pocket draws lubricant into the contact, and iii ) film thickness decay as oil is squeezed out of the contact. The interplay of these three mechanisms is shown to control the response of micro-textured surfaces under all lubrication regimes.

An investigation was carried out to study the effect of changes in oil quality on its tribological performance using a tuning fork technology based oil sensor. In this research, a tribological testing system was commissioned, to simulate the piston ring-cylinder liner sliding contact, and to measure the lubricant condition in real-time using an oil sensor. Tribological contact between cylinder liners and piston rings in marine engines is the most affected region due to excessive thermo-mechanical stresses. At top dead centre, the effect of such stresses is at a maximum where piston-sliding speed is lowest, while the temperature is high due to fuel combustion, and radial load behind the piston rings compressing against the cylinder liner surface is at a maximum due to gas pressure and the compression fit of piston rings within the cylinder liner. At bottom dead centre, this effect is less severe due to a reduction in temperature and gas pressure on the piston rings, as the piston is positioned away from the combustion chamber. These two regions experience boundary lubrication conditions, where anti-wear and anti-friction additives are responsible for forming a protective lubricious film on sliding surfaces. At mid-stroke, piston-sliding speed is maximum, therefore, a full hydrodynamic film is formed in this region separating the piston rings and cylinder liner. The formation of oil film depends upon, the physical properties of oil (such as viscosity and density) under hydrodynamic lubrication conditions, and the oil chemistry (such as presence of additives in oil) under mixed or boundary lubrication conditions. Lubricants in marine engines undergo intense degradation in quality due to contamination with wear particles, water, soot, un-burnt fuel, coolant, and additives depletion. Such degradation of lubricants leads to a reduction in their capability to form a minimum thickness of oil film between two moving engine components to avoid direct metal-to-metal contact, which may cause wear. Therefore, monitoring the condition of marine engine lubricants is vital in order to predict any significant change in its quality. The results obtained from tribology testing and oil condition monitoring in the current research showed a good correlation and are useful to understand the performance of lubricants for piston ring-liner contacts.

One of the several losses of a combustion chamber is the gas leakage toward the crankcase due to imperfect sealing of the rings, it is commonly known as blow-by and it affects efficiency and emissions. One important factor affecting it is the distorted cylinder bore. The paper describes the equations that rule the blow-by phenomenon in terms of ring and gas dynamics, subsequently, the bore distortion of the cylinder was obtained and its orders calculated through Fourier series. The ringpack capacity in the distorted bore cylinder was then analysed using ©Ricardo RINGPAK Solver. Order zero distortion resulted to be the most important order due to the highest amount of gas lost in the crankcase. Orders one and two didn’t showed significant differences from the non-distorted bore case, while orders three and four resulted in high blow-by values, even if their magnitude of distortion was lower in comparison to other orders. The ring pack behavior showed to be affected by bore distortion and its magnitude, however, the blow by phenomenon showed to depend also on other factors in a complex manner.

The aim of this study is to gain insights into the interactions between laser-textured surface pockets and friction and wear behaviour of an automotive piston-liner pairing. To do this, a recently developed, reciprocating, test apparatus was used to conduct wear tests under highly loaded conditions. Fused silica specimens with a range of pocket geometries were rubbed against a convex steel pad and the resulting friction and wear data were compared with those from a non-textured specimen. Contact conditions were set to remove the influence of initial surface roughness on texture behaviour. These tests showed that, as the specimen become worn and surface roughness increases, the contact progresses further into the mixed and boundary regime. This leads to a significant improvement in the relative performance of the textured specimens, showing reductions in friction of up to 70%, compared with the non-texture case. This is consistent with previous results that have shown texture to have the effect of boosting film thickness in the mixed lubrication regime. Surface texture was also shown to reduce the volume of wear, by up to 69% (corresponding to a change in wear coefficient from 2.67e−4 to 0.81e−4 [mm3/N m]). Another, important, finding is that both friction and wear reduce monotonically as the sum of the pocket volumes along the stroke increases. This may aid texture design, since it means that individual pocket width and depth values can largely be ignored, so long as the overall volume is maximised. The only exception to this trend is when the pockets are larger than the contact area. In this case, friction increases due to a collapse of the lubricant film, while wear reduction remains unaffected – a discrepancy which may suggest that pockets reduce wear and friction via separate mechanisms.

Applying surface texture to piston liners may provide an effective means of controlling friction and hence improving engine efficiency. However, little is understood about the mechanisms by which pockets affect friction, primarily because of a lack of reliable experimental measurements. To address this, the influence of surface texture on film thickness and friction force was measured simultaneously in a convergent-divergent bearing, under conditions that closely replicate an automotive piston ring-liner conjunction. Film thicknesses were measured using a modified version of the ultra-thin film optical interferometry approach, enabling film thicknesses

Development and production of piston rings made of sintered materials on the basis of iron powder metallurgy is an innovative way. In the application of this technology reduces the consumption of material and costs for the production of piston rings 30-40% in comparison with the traditional methods of their manufacture

Поршневые кольца в процессе эксплуатации подвергаются износу. Недостаточная износостойкость материалов поршневых колец зачастую лимитирует рост производительности машин и сроков их эксплуатации. Не всегда требуемый комплекс свойств поршневых колец, изготовленных из чугуна, может быть достигнут традиционными методами термической или химико-термической обработки. Так, применение традиционных способов борирования, связанных с диффузией бора в твердую фазу, приводит к формированию рабочего слоя, обладающего высокой хрупкостью. Поэтому актуальной является проблема повышения износостойкости поршневых колец без охрупчивания. Применение лазерного нагрева при борировании обеспечивает образование нового слоя с особыми свойствами. Однако оптимальные свойства могут быть достигнуты только после установления взаимосвязи между параметрами проведения процесса и глубиной борированного слоя. Целью работы было установить влияние параметров лазерного нагрева на состав и глубину борированного слоя, так как свойства поршневых колец зависят от глубины последнего. В результате проведенных исследований установлено, что возрастание скорости перемещения детали в процессе лазерного нагрева уменьшает глубину борированного слоя. Такая зависимость наблюдается как при толщине обмазки 0,15 мм, так и при толщине 0,30 мм. При всех скоростях перемещения образца для использованной боросодержащей обмазки с указанными толщинами большая толщина борированного слоя и зоны термического влияния отвечает большей толщине обмазки. Увеличение диаметра пятна повышает глубину слоя. Рентгенографически и металлографически расшифрованы фазы и структурные составляющие борированного слоя. Рентгеноструктурным и микроструктурным анализом выявлена связь между скоростью облучения и долей высокобористых структур в слое. Показано, что борированный слой в высокопрочном чугуне содержит такие фазы, как FeB, Fe2B, α-фазу, бороцементит Fe3(B,C). Результаты исследований могут быть распространены и на другие детали, подвергающиеся интенсивному износу., Problem. Piston rings in the process of operation are subject to wear. Non-sufficient wear resistance of piston ring materials often limits the growth of productivity of machines and the timing of their operation. It is not always that the desired set of properties of piston rings made of cast iron can be achieved by traditional methods of thermal or chemical-thermal treatment. Thus, application of traditional boriding methods associated with diffusion of boron into the solid phase leads to formation of the working layer having high brittleness. Therefore, the actuality of the problem is to increase the wear resistance of piston rings without embrittlement. Use of laser heating at boriding provides the formation of a new layer with special properties. However, the optimum properties can only be achieved after establishing a relationship between the parameters of running a process and the depth of the borated layer. The goal was to determine the effect of laser heating parameters on the structure and depth of the borated layer, since the properties of piston rings depend on the depth of the latter. The studies conducted revealed that the increase in the speed of displacement of the part in the process of laser heating reduces the depth of the borated layer. Such a dependence is observed both at 0.15 mm thickness of coating and at a thickness of 0.30 mm. For all modes of workpiece displacement speed for the used boron containing envelope with the above-specified thickness a higher thickness of the borated layer and the heat affected area corresponds to a higher thickness of coating. Increase of the spot size leads to an increase in the depth of the layer. By X-ray and metallographic diffraction there were decoded the phases and structural constituents of the borated layer. X-ray diffraction and microstructural analysis revealed an association between the exposure speed and share of high-boron layer structures. It is shown that the borated layer in the ductile iron includes such phases as FeB, Fe2B, α-phase, and borocementite Fe3 (B, C). The research results can be extended to other parts subject to intensive wear., Поршневі кільця в процесі експлуатації підлягають зношуванню. Недостатня зносостійкість матеріалів поршневих кілець часто обмежує зростання продуктивності машин і терміну їх експлуатації. Не завжди потрібний комплекс властивостей поршневих кілець, виготовлених з чавуну, може бути досягнутий традиційними методами термічної або хіміко-термічної обробки. Так, використання традиційних способів борування, пов’язаних з дифузією бору в тверду фазу, приведе до формування робочого шару, що має високу крихкість. Тому актуальною є проблема підвишення зносостійкості поршневих кілець без окрихчування. Використання лазерного нагріву при боруванні забезпечує утворення нового шару з особливими властивостями. Однак оптимальні властивості можуть бути досягнуті тільки після встановлення зв’язку між параметрами проведення процесу і глубиною борованого шару. Метою роботи було встановити вплив параметрів лазерного нагріву на склад та глибину шару борування, так як властивості поршневих кілець залежать від глибини останнього. В результаті проведених досліджень встановлено, що збільшення швидкості переміщення деталі в процесі лазерного нагріву зменшує глибину шару борування. Така залежність спостерігається як при товщині обмазки 0,15 мм, так і при товщині 0,30 мм. При всіх швидкостях переміщення зразка для використаної обмазки, що містить бор, із вказаними товщинами більша товщина борованого шару та зони термічного впливу відповідає більшій товщині обмазки. Збільщення діаметру плями сприяє зростанню глибини шару.Рентгенографічним і металографічним методами розшифровані фази і структурні складові шару борування. Рентгенографічним і металографічним аналізом визначений зв’язок між швидкістю опромінення і часткою високобористих структур в шарі. Показано, що борований шар в високоміцному чавуні містить такі фази, як FeB, Fe2B, α-фазу, бороцементит Fe3(B, C).Результати досліджень можуть бути поширені і на інші деталі, що підлягають інтенсивному зношуванню.

Recent experiments have shown that automotive piston-liner friction may be reduced by up to 50 % if the surface of the liner is laser textured with certain configurations of micro-pockets. It is important to model this behavior to understand and optimize the friction reduction mechanisms that are occurring. However, until now, very few models that predict the lubrication performance of textured surfaces have been successfully validated against experimental data. This is because of the requirement for them to: (1) reproduce experimental configurations with a certain degree of fidelity, (2) conserve mass properly, and (3) account for transient, boundary lubrication conditions. To address this, the current paper presents a comparison between the results from a numerical model, which fulfils these criteria, and an experimental test rig operating under the same conditions. The mathematical modeling is based on the averaged Reynolds’ equation with Patir and Cheng’s flow factors and the p − θ Elrod–Adams mass-conserving cavitation model. Simultaneously to the fluid flow solution, the contact pressures that arise from the asperity interactions are also included into the calculations through the well-known stochastic Greenwood and Tripp model for rough contacts. The experimental data is produced using a reciprocating tribometer, whose contact conditions are closely controlled and accurately mimic those found in an automotive piston–liner conjunction. Data is presented in terms of friction force versus stroke angle, and the similarities and differences between the model and experiment are discussed.

In a high speed hydraulic actuator the usage of seals on the piston surface causes excessive wear on the seals and positional inaccuracies owing to coulomb friction. Hence sealless pistons with sloping surfaces have been tried by some manufacturers of such actuators. Here an attempt is made to analyse systematically the three types of profiles commonly considered for high speed actuators, using Reynolds' differential equation. Analyses are made using an analytical method for one-dimensional flow and using the finite element method for two-dimensional flow. The analyses reveal that single tapered pistons have certain limitations and that double tapered pistons can function successfully under different conditions in hydraulic actuators. It is also shown that friction in these types of pistons is much less than in conventional pistons with seals.