Textured Piston Research Articles

Stability Analysis of the Secondary Motion of a Textured Piston

Piston–cylinder pairs are very common in industrial mechanisms. While a piston is primarily designed for axial reciprocating motion, the occurrence of secondary motions—lateral and rotational—due to the small clearance between the piston and the cylinder may lead to frictional contact, energy loss, wear and an increase in unwanted leakage. This study focuses on mitigating the secondary motion of a ringless piston. The influence of a Rayleigh step bearing and partial surface texturing with numerous micro-dimples on the dynamic stability of the secondary motion is studied. A linear model was used to obtain the trajectory of the secondary motion and Floquet theory was applied to analyze the stability and draw stability maps. The influence of various texturing and step parameters, including the dimple area density and aspect ratio for partial texturing, as well as the length and depth of treatment for both partial texturing and step profiles, on the stability of the secondary motion was examined. The normalization method is presented, enabling the expansion of the results for various operating conditions and geometries. Conclusions and guidelines regarding the optimal parameters, in terms of a wider stability range and higher decay rate, are formulated.

Deterministic Simulation of Surface Textures for the Piston Ring/Cylinder Liner System in a Free Piston Linear Engine

The use of synthesis gas (SYNGAS) from waste gasification has been pointed out as a key strategy to help the energy transition. However, SYNGAS’ low calorific power is considered a difficult obstacle to its technological use in internal combustion engines. To overcome this, a novel free-piston linear motor has been proposed to pave the way for the use of SYNGAS in the mobility sector. Surface texturing has vast potential to reduce friction losses in this system. This study utilizes a deterministic numerical model to investigate the mixed lubrication performance of a textured piston ring/cylinder liner conjunction in a free piston engine. The model considers the simultaneous solution of the lubrication and asperity contact problems at the roughness scale, including texturing features on the cylinder surface. The numerical model employs the Reynolds equation with mass-conserving cavitation to calculate the inter-asperity fluid pressure. The rough contact model utilizes the Hertz theory for elastic contact to calculate the contact pressure at each asperity between the piston liner surface and the admitted smooth and rigid ring surface. Surface texturing demonstrated remarkable effectiveness, particularly in the hydrodynamic lubrication regime, with a maximum friction reduction of 38.5% observed for an area coverage of 50%. This was accompanied by a notable shift in the transition from the boundary to the mixed lubrication regime. The textured surfaces exhibited consistent efficiency in reducing fluid pressure and shear stress as the coverage of the textured areas increased. The incorporation of dimples on these surfaces played a crucial role by augmenting the lubricant storage capacity while concurrently reducing the real shear and contact areas. This study offers valuable insights into the nuanced friction-reducing mechanisms of surface textures, illuminating their influence on the coefficient of friction and the formation of lubricant films across various lubrication regimes.

The testing and optimization of a bio-inspired textured piston for the BW-250 mud pump

To reduce the friction, wear, and temperature of the piston-cylinder liner friction pair, we designed and processed 27 kinds of bio-inspired textured pistons with cylindrical pits. Based on the experimental optimization design method, friction test, wear test, and thermal imaging test were carried out. Results show that the textured pistons can significantly reduce the friction. Various texture parameters have different effects on the mean friction force. The wear of the textured pistons is significantly less than that of the standard piston. The influence of the texture parameters on piston wear are analyzed through range analysis, regression equation, and 3D response surface method. The standard piston suffers from serious wear and tear. The cylindrical pit texture can supply lubrication and store abrasive particles, which can improve the wear condition of the textured piston surface to a certain extent. The friction heat of the textured pistons is small, which can reduce the average temperature of the friction pair.

Inspired by Earthworms and Leeches: The Effects of Cylindrical Pit Arrays on the Performance of Piston-Cylinder Liner Friction Pairs

To improve the friction and wear performance of the piston-cylinder liner friction pair, inspired by earthworms and leeches, 27 kinds of pistons with cylindrical pit arrays are designed and processed. Through a friction test, four superior textured pistons are optimized, and wear, life and thermal imaging tests are performed. Finite element analysis of the friction pair model is performed, and the friction and wear mechanisms are discussed. The results show that the pistons with cylindrical pit arrays have excellent friction and wear performance, less heat generation by friction, longer lives and less scratches on the cylinder liner. The temperature of the optimized textured pistons was reduced by around 5–10 °C. The wear amount of some textured pistons was reduced by over 50%, resulting in an improvement in their lifespan of at least 30% or more. The results of the finite element analysis indicate that the textured piston exhibited reduced deformation and favorable stress–strain distribution and satisfied the required contact pressure.

Design, manufacturing, and testing of a laser textured piston ring surface reinforced with a CuCoBe–diamond composite by hot-pressing

A CuCoBe–diamond composite was used to reinforce a laser textured 410 stainless steel piston ring by hot-pressing. Different hot-pressing parameters were used to optimize the sintering process of the CuCoBe particles (P = 25 and 50 MPa, T = 820 and 980 °C, and t = 15 and 30 min). The results showed an increase in the hardness of the hot-pressed samples (50.5% and 48.5% for P = 25 and 50 MPa, respectively). Three textures with different track widths and distances between them were produced by laser on the compression piston rings’ surface. The composite powders were used for the reinforcement of the textures by hot-pressing at the optimized sintering parameters (T = 980 °C, P = 25 and 50 MPa, and t = 15 min). The tribological results revealed that larger texture dimensions led to enhanced tribological performance.

Effect of Groove Texture on Deformation and Sealing Performance of Engine Piston Ring

During the present study, a double groove texture was designed on the surface of a piston ring to improve the sealing performance between the piston ring and cylinder liner. The experimental design method was used to fabricate the test plan according to the groove width, depth, and spacing. By using the thermal–structural coupling analysis method, the finite element analysis of the standard piston ring and the textured piston ring was carried out to simulate the deformation state of the cylinder liner system of the piston ring group during the working stroke. The piston rings with different parameters designed by the test scheme were manufactured by wire electrical discharge machining, and the self-made experiment device carried out the sealing test. The results showed that the groove texture could improve the sealing performance of the piston ring, and the analyzed results demonstrated that the groove texture had little effect on the maximum deformation of the piston ring. Still, it could significantly reduce the minimum deformation of the piston ring group. A piston ring with groove texture would improve the sealing performance and reduce the deformation during the work stroke. During the test, the average deformation of the No.7 piston ring group, with a groove depth of 1 mm, a groove width of 0.5 mm, and a groove spacing of 0.1 mm, was the smallest, about 29.6% lower than that of the standard piston ring group. The sealing performance of the No.7 piston ring group was the best, and the reduction rate of the top gas leakage rate was 52.18%. During the present study, the sealing performance of the piston ring was improved by designing the grooved structure on the piston ring surface, thereby improving the fuel economy and power performance of the engine. The present study could provide a reference for the engineering field to design a piston ring with high sealing performance.

Analysis of lubrication and sealing performance on textured piston pair with multi-factor coupling

PurposeThis paper aims to study the lubrication and sealing performance on the textured piston pair under the cross action of the shape and structure parameters. This paper further carries out the optimization design of low energy consumption hydraulic impact piston pair.Design/methodology/approachBased on the characteristics of the ring gap seal piston pair, the flow field analysis model of the whole film gap is established for its periodic treatment. The friction power loss of the piston pair is defined as the evaluation index of the lubrication performance and the leakage power loss as the evaluation index of the sealing performance. The orthogonal test design and CFD software were used to analyze the lubrication and sealing performance of the textured piston pair.FindingsThe cross action of shape and structure factors has a great influence of the lubrication and sealing performance on the textured piston pair. Clearance and shape parameters have great influence on it, while seal length and depth diameter ratio have little influence. The sealing performance of conical textured piston pair is good, while the lubrication performance of square textured piston pair is good. The primary and secondary order of influence of shape and structure on energy consumption on piston pair is B (seal clearance) > C (texture shape) > D (area ratio) > A (seal length) > E (depth diameter ratio).Originality/valueBreaking the defect of local optimization design on traditional piston pair structure, then find the matching relationship of structural parameters on textured piston pair. Further improve the lubrication and sealing performance of the piston pair, and provide reference for the global optimization design of the low energy consumption hydraulic impact piston pair.

Synergistic effect of textured piston ring and nano-lubricant on performance parameters and emissions of IC engine

Internal combustion (IC) engine is a prime emitter of greenhouse gases. The piston ring-cylinder liner pair plays a critical role in engine performance and exhaust emissions. Moreover, it accounts for major engine losses. The texturing on the piston ring and nano-material blended engine oil (nano-lubricant) have demonstrated promising results in their respective investigations on the IC engine. So far, most of the studies have been conducted on one of these approaches. Therefore, in this study synergistic effect of textured piston ring and nano-lubricant is investigated on performance parameters (fuel consumption, brake thermal efficiency, and brake specific fuel consumption) and engine emissions. The upper top compression piston ring is textured partially, and the nano-lubricant is prepared using silicate complexes nano-material [Mg6SiO10(OH)8] of 1% by weight with multi-grade engine oil (20W-40). The laser surface texturing technique (LST) is used to produce cylindrical textures on the piston ring with 6% texture density and 7.5% aspect ratio. Experiments have been conducted on a single-cylinder, direct injection, air-cooled, naturally aspirated compression ignition engine. All tests have been performed under different loading conditions (20%, 40%, 60%, 80% and 100% of full load). The synergistic effect of partially textured piston ring and nano-lubricant showed lower fuel consumption up to 4.58%, and nano-lubricant showed fuel reduction up to 3.23%. Furthermore, the exhaust emissions (CO, HC, and NOx) demonstrated a reduction that ranges from 0.24% to 10% compared to baseline data.

Performance analysis of two-dimensional section of partially textured piston ring with cavitation boundary conditions

The lubrication problems for cavitation are solved using the Elrod algorithm/its modifications, which are extremely nonlinear in nature due to binary switch function, lead to convergence issues, consequently, prone to numerical instabilities. In the present study, a continuous switch function is used to avoid these issues, which has not been explored yet for investigating performance behaviours (minimum film thickness, friction force, and power-loss) of piston ring/cylinder liner pair. The modified Reynolds equation is discretized using the Finite Difference Method (FDM). The algebraic equations have been solved by employing the Elrod and Vijayaraghavan-Keith algorithm with a modified switch function proposed by Fesanghary-Khonsari, which satisfies the mass-conservative cavitation. On the other hand, the total computational domain plays a significant role in predicting accurate numerical results. Therefore, in the present investigation, a piston ring segment of 3 mm × 1.20 mm has been investigated, which comprises larger computational domains ever considered in previous studies. The textures are cylindrical and situated at both ends of the piston ring, leaving the center portion untextured in the axial direction. The minimum film thickness change with time (squeeze film action) and lubricant’s (SAE 20W-40 engine oil) viscosity change with operating temperature have been incorporated in the spectrum of this study. The textured piston ring demonstrated an increase up to 7.2% of the minimum film thickness, friction reduction up to 30%, and reduction in power-loss up to 11% compared to the conventional (un-textured) piston ring.

Femtosecond Pulsed Ti:Sapphire Laser-Assisted Surface Texturing on Piston Ring and Its Tribology Characterization

Abstract Femtosecond laser-assisted surface texturing of compression piston rings is proposed and demonstrated. A femtosecond pulsed Ti3+:sapphire laser is used to generate dimples of the same size but with different area density on a moly-chrome ceramic deposited cast iron piston ring. The influence of the surface morphology and tribology operating conditions, such as reciprocating frequency and temperature of the lubricant, on friction and wear characteristics of textured piston rings and plateau honed liner samples is investigated. A decrease in the friction coefficient is observed with the texturing of rings. The dimple area density, which is defined as the ratio of the total textured area and the total area of the surface, of 16% and 27% offered a reduced coefficient of friction and minimize wear on the liner surface.

An isogeometric analysis approach for solving the Reynolds equation in textured piston ring – cylinder liner contacts

PurposeThe purpose of this study is to propose an isogeometric analysis (IGA) approach for solving the Reynolds equation in textured piston ring cylinder liner (PRCL) contacts.Design/methodology/approachThe texture region is accurately and conveniently expressed by non-uniform rational B-splines (NURBS) besides hydrodynamic pressure and the oil film density ratio is represented in this mathematical form. A quadratic programming method combined with a Lagrange multiplier method is developed to address the cavitation issue.FindingsThe comparison with the results solved by an analytical method has verified the effectiveness of the proposed approach. In the study of the PRCL contact with two-dimensional circular dimple textures, the solution of the IGA approach shows high smoothness and accuracy, and it well satisfies the complementarity condition in the case of cavitation presence.Originality/valueThis paper proposes an IGA approach for solving the Reynolds equation in textured PRCL contacts. Its novelty is reflected in three aspects. First, NURBS functions are simultaneously used to express the solution domain, texture shape, hydrodynamic pressure and oil density ratio. Second, the streamline upwind/Petrov–Galerkin method is adopted to create a weak form for the Reynolds equation that takes the oil density ratio as a first-order unknown variable. Third, a quadratic programming approach is developed to impose the complementarity conditions between the hydrodynamic pressure and the oil density ratio.

Effect of fish scale texture on friction performance for reciprocating pair with high velocity

PurposeThis paper aims to study the frictional performance of reciprocating pair with high velocity by using hydrodynamic lubrication principle and fish scale textured piston model.Design/methodology/approachBased on the idea of function characteristic approximation and coordinate change, a mathematical representation model of imitating fish scale texture pit section is established. According to the principle of dynamic pressure lubrication of the textured fluid, a three-dimensional numerical model of flow field for fish scale texture is established without considering cavitation. Numerical analysis of the model carp scale texture unit by orthogonal experimental design and FLUENT software is carried out.FindingsEffects of fish scale pit texture on friction properties for a reciprocating pair piston surface with high velocity (impact piston) are acquired. Effects of texture characterization parameters and flow rate on the surface friction performance for impact piston are found. Effects of different characteristic parameters combination of imitating fish scale texture on friction performance for impact piston surface are obtained.Originality/valueThe model is an effective tool to study the friction and wear of reciprocating pair with high velocity. The effects of fish scale textured piston pair supply a theory lead to design the reciprocating pair with better friction performance.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2019-0398

Influence of positive texturing on friction and wear properties of piston ring-cylinder liner tribo pair under lubricated conditions

Purpose In an internal combustion engine, piston ring-cylinder liner tribo pair is one among the most critical rubbing pairs. Most of the energy produced by an internal combustion engine is dissipated as frictional losses of which major portion is contributed by the piston ring-cylinder liner tribo pair. Hence, proper design of tribological parameters of piston ring-cylinder liner pair is essential and can effectively reduce the friction and wear, thereby improving the tribological performance of the engine. This paper aims to use surface texturing, an effective and feasible method, to improve the tribological performance of piston ring-cylinder liner tribo pair. Design/methodology/approach In this paper, influence of positive texturing (protruding) on friction reduction and wear resistance of piston ring surfaces was studied. The square-shaped positive textures were fabricated on piston ring surface by chemical etching method, and the experiments were conducted with textured piston ring surfaces against un-textured cylinder liner surface on pin-on-disc apparatus by continuous supply of lubricant at the inlet of contact zone. The parameters varied in this study are area density and normal load at a constant sliding speed. A comparison was made between the tribological properties of textured and un-textured piston ring surfaces. Findings From the experimental results, the tribological performance of the textured piston ring-cylinder liner tribo pair was significantly improved over a un-textured tribo pair. A maximum friction reduction of 67.6 per cent and wear resistance of 81.6 per cent were observed with textured ring surfaces as compared to un-textured ring surfaces. Originality/value This experimental study is helpful for better understanding of the potency of positive texturing on friction reduction and wear resistance of piston ring-cylinder liner tribo pair under lubricated sliding conditions.

Femtosecond laser assisted generation of micro-dimples on moly-chrome film for improving its tribology

Femtosecond laser ablation of the moly-chrome deposited piston ring and the influence of laser fluence and number of laser pulses on dimple morphology and geometry were analysed. The increase of laser fluence and pulse numbers beyond 8.4 J/cm2 affected the dimple surface by inducing severe cracks due to heat accumulation. Based on the experimental investigation, the ablation threshold for moly-chrome film was found to be 0.36 J/cm2. Textured surface was formed on the moly-chrome film with laser fluence near the ablation threshold and the tribological characteristics were studied. The piston ring surface was textured with dimple diameter of 100 μm and dimple aspect ratio of 0.2. Effect of different dimple area ratios, such as 2%, 16% and 38% were analysed by reciprocating type tribology testing. The textured surface with 16% dimple area ratio showed a reduction in friction compared to the plain and the remaining textured piston rings.

Transient Thermal Hydrodynamic Lubrication Analysis of Textured Piston Ring/Cylinder Liner

On the basis of transient thermal hydrodynamic lubrication (TTHL) simulation and isothermal hydrodynamic lubrication (IHL) simulation of textured piston ring/cylinder liner, main factors influencing oil film temperature, distribution of the maximum temperature, and comparison between two models were discussed. The results show that texturing improves hydrodynamic lubrication situations, and velocity of piston ring and applied load are two important factors affecting oil film temperature. Apart from that, sever temperature elevation is located at the export of oil film and textured areas. Although change trends of the maximum of pressure and the minimum of oil film thickness are basically the same, the values of them are different. Temperature is a necessary element for analyzing the lubricant situations of piston ring/cylinder liner.

Research on the Profile Design of Surface Texture in Piston Ring of Internal Combustion Engine

In this paper, a profile design of surface texture was applied for improving the tribological performance of piston ring–cylinder pair. The design of texture pattern was implemented by numerous textures of different depths in sliding speed direction to imitate the outline of barrel-shaped ring. The thickness and pressure distribution of oil film were obtained through a joint solution of modified Reynolds equation and other governing equations for textured surface. The results indicate that the novel texture pattern has the best overall performance in oil film thickness and friction force compared with normal surface textures, and the average friction power is 10.04% and 16.85% less than normal surface textures and barrel-shaped ring in the whole working cycle. Extra microhydrodynamic lubrication can be observed in the middle region of textured piston ring through the pressure distribution of oil film. At last, the experiment was conducted in a motored test rig and exhibited up to 3% reduction in friction power.

Numerical analysis of textured piston compression ring conjunction using two-dimensional-computational fluid dynamics and Reynolds methods

The Reynolds equation, in which some items have been omitted, is a simplified form of the Navier–Stokes equations. When surface texturing exists, it may unreasonably reveal the tribological effects in some cases. In this paper, both the two-dimensional computational fluid dynamics method, which is based on the Navier–Stokes equations, and the corresponding one-dimensional Reynolds method are adopted to analyze the performance of the textured piston compression ring conjunction. To conduct a comparison between these two methods, the modified Elrod algorithm for Jakobsson–Floberg–Olsson cavitation model is chosen to solve the Reynolds equation. The results show that the Reynolds method is somewhat different from the computational fluid dynamics method in the minimum oil film thickness, pressure distribution, and cavitation at given operating conditions. Moreover, for a low ratio of texture depth to length, the Reynolds equation is still suitable to predict the overall effects of the designed groove textures. The simulation results also reveal that it is not always beneficial for the tribological performance and sometimes may increase the total friction force when the ring is textured.

Looking into a laser textured piston ring-liner contact

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).

Numerical investigation of tribological performance in mixed lubrication of textured piston ring-liner conjunction with a non-circular cylinder bore

A number of inevitable factors distort the liner circular bore, resulting in asymmetry of piston ring-liner (PRL) contact in the circumferential direction. The limited conformability of a piston ring causes a gap in PRL contact, which has significant effect on the tribological performance of the interface. Recent developments in ring surface modification through laser surface texturing have shown promising results in improving tribological characteristics. Analyses of a textured piston ring are often based on ideal circular liner bore, which is contrary to actual engine operating conditions. In this study, asymmetric PRL contact of a textured piston ring in a distorted bore is considered, and the 2D Reynolds equation is solved with a mass-conserving cavitation algorithm. In addition, asperity interaction in mixed lubrication, axial ring dynamics, variable ring conformability, and realistic engine oil rheology are considered in the investigation of tribological performance of a non-axisymmetric textured PRL interface. Results show that optimized surface textures improve the tribological performance of a PRL interface, whereas textures with large lateral aspect ratios have a detrimental effect. The surface texturing-induced increase in oil transport to the combustion chamber remains minimal.

Modeling and simulation of frictional energy loss in mixed lubrication of a textured piston compression ring during warm-up of spark ignition engine

Road vehicles account for a substantial portion of energy consumed by transportation. A large amount of this energy is lost to overcome friction within vehicle engines, in which the piston compression rings are a major source of such parasitic losses. The internal losses of engines increase several times in the case of unfavorable warm-up conditions. Recent developments in surface modification showed promising results in improving the frictional behavior of piston rings. Analyses are often idealized, such as isothermal conditions and unrealistic engine operating conditions. This study presents a numerical investigation of the frictional behavior of mixed-hydrodynamic interaction in a textured piston compression ring–cylinder liner during the warm-up process. The transient Reynolds equation is solved with a mass-conserving cavitation algorithm, realistic oil rheology, and practical engine operating conditions. Several multigrade and monograde oils are considered to draw comprehensive conclusions. The results show that ring surface texturing substantially reduces energy loss during the entire warm-up phase.