Lubricant Viscosity Stability Under High Temperature

Bearings are common components used in the transmission system of tool machinery and linear drive equipment.With increasing demand for higher efficiency and faster production under the required accuracy, the control of bearing temperature rise under high operational speed becomes a critical issue.The improper control of temperature rise can lead to the thermal deformation and life reduction of the machinery.Conventionally, a circulating oil lubrication system is utilized with journal bearings.In this study, a similar lubrication system was adopted for the ball bearing with a retrofit design.Three control factors, i.e., rotational speed, bearing preload, and the viscosity of the lubricant used, were chosen to study their effects on the temperature performance of the proposed lubrication system.Experimental measurements showed that the lubrication system was able to lower the temperature rise of the bearing considerably compared with its unlubricated counterpart, especially at high rotational speeds.Even with the enhanced cooling from the oil circulation system, temperature rise still ... Read More

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Bio-lubricants are the future of lubricants as a substitute for mineral lubricants; however, bio-lubricants have drawbacks, such as poor thermal-oxidative stability. In addition, during the friction process, the temperature of the lubricant increases, so the lubricant must have good thermal conductivity to conduct heat to the environment. To combat the drawbacks of bio-lubricants, some additives have been used to improve their performance as lubricants. Composites of carboxymethyl cellulose (CMC)/MXene and Span 60 as surfactants were used as additives in CPO with different compositions. The physicochemical properties of the addition of CMC/MXene and Span 60 in CPO have changed, including kinematic viscosity, TAN, thermal conductivity, and fatty acids, which have a positive impact on lubrication performance in terms of reducing oxidation processes and increasing thermal conductivity. From fatty acid composition tests and FTIR analysis, the additives work to suppress the oxidation process. A pin-on-disk test was performed to evaluate the tribological performances of bio-lubricants. The... Read More

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Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finall... Read More

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Lubricating compositions that maintain viscosity stability and prevent oxidative degradation when contaminated with biodiesel, comprising a base oil, sulfurized additives, boronated dispersants, and a detergent system with a specific sodium-to-magnesium ratio and sulfur-to-sodium ratio. The detergent system provides a controlled level of soap content and metal ions, while the sulfurized additives and boronated dispersants contribute to oxidative stability. The composition is particularly effective in preventing viscosity increase when contaminated with up to 30% biodiesel, as demonstrated by passing the GFC Lu-43-A-11 test.

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One of the main characteristics of lubricants is the viscosity index, which shows the dependence of oil viscosity on temperature. The higher the viscosity index, the better the lubricating properties of the oil. Esters of various polyols, in particular pentaerythritol, are very effective in this direction. This work examines a wide range of high-purity pentaerythritol esters of 14 compounds of varying degrees of branching and studies the temperature dependences of kinematic viscosity in the temperature range from melting temperatures to 150C. Based on the obtained data, the values of viscosity indexes were calculated, and the contribution of the carboxylic acid structure to the viscosity properties was also considered.

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As countries prioritize climate change concerns, promoting the use of new environmentally friendly working fluids has become a common goal for the industry. In thermal systems, lubricants come into contact with these working fluids and directly affect their utilization efficiency. Therefore, investigating the effect of lubricant mixing on the physical properties of process media is essential to promote the adoption of new environmentally friendly working fluids. This paper categorizes and organizes recent research literature on working fluids and lubricants. It was aimed to comprehend the effect of lubricants on the operating characteristics of working fluids. By comparing the research methods and experimental equipment utilized in previous studies, this work analyzes the variation of basic physical properties, including miscibility, solubility, viscosity, and gas-liquid phase equilibrium. In addition, the effects of lubricant mixing in terms of heat exchange characteristics, additives, and material compatibility are also summarized. These findings provide a reference for achieving o... Read More

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ABSTRACT Lubricants play a crucial role in reducing friction and wear between surfaces in relative motion. Engine oil, as a lubricant, is specifically designed to minimize friction and wear between the moving parts of different equipment and machinery. Engine oil blending serves the purpose of adjusting the variety of lubricants available to meet specific performance requirements. Through blending, it is possible to tailor the characteristics of the lubricating oil, such as viscosity, stability, and additive content, to optimize its effectiveness in reducing friction, protecting engine components, and enhancing overall equipment performance. By customizing lubricant formulations through blending, manufacturers can address the diverse lubrication needs of modern engines and machinery, ensuring smooth operation, longevity, and efficiency.To enhance the quality of the lubricant and achieve the desired high-performance multi-grade engine oil, a systematic approach was followed. The process began with testing the specific gravity of the oil using a hydrometer and thermometer to ensure acc... Read More

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Achieving appropriate miscibility, solubility, and working viscosity between a lubricating oil and a refrigerant is vital for proper compressor performance. These properties are all interrelated and cannot be optimized independent of one another; the thermodynamics that define one interaction also influence the others. Choosing the best fluid combination is therefore a tradeoff between the different properties, making it critically important to understand their possible behaviors. This paper will investigate the range of liquidliquid miscibility behaviors and explore the resulting solubility and working viscosity outcomes. Different lubricant chemistries will be tested to demonstrate the impact of lubricant chemical family on performance, as well as looking within a chemical family to show how finely tuned chemistry choices can shift test results. The outcome from this investigation will help compressor engineers design more reliable and energy-efficient systems.

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Abstract Most studies of liquid lubricants were carried out at temperatures below 200 C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si 3 N 4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 C, coefficient of friction (COF) remains at 0.130.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.20.3. At 200 C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.160.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with t... Read More

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When exposed to high surface temperatures, engine lubricating oils degrade and may form solid deposits, which cause operational issues and increase shutdown time and maintenance costs. Despite its being a common issue in engine operation, the information available on the mechanics of this phenomenon is still lacking, and the experimental data and conditions must be updated to match the improvements in both lubricant stability and engine efficiency. To this end, an experimental apparatus has been developed to study the mechanisms that lead to the degradation and deposit formation of lubricants at high temperatures. The apparatus is designed to operate at pressures up to 69 bar, surface temperatures up to 650 C, oil bulk temperatures up to 550 C, and flow rates of <14 mL/min. In this apparatus, the oil is cycled through a heated test section, and deposits accumulate on the heated surface. The time required for deposits to start accumulating under the test conditions is determined based on the recorded temperature traces, and collected oil and deposit samples may be analyzed to... Read More

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The paper presents the results of studies aimed at defining the effect of the cooling properties of oil lubricants used in various metalworking processes. The design and a brief description of the installation are given, which allows to obtain temperature-time, temperature-velocity dependencies of various liquids. The use of this installation gives the opportunity to select lubricants according to its cooling properties, depending on the temperature range required by the process. The assessment results of lubricant cooling properties at UZS-2 installation, manufactured according to the requirements of international standards ISO 9950, ASTM D6200 - 01 and ASTM D6482 06 are presented. The dependences of tribo-engineering properties of the tested oil lubricants on their cooling characteristics are found out. It is shown that with an increase in the temperature at which the maximum cooling rate of the lubricant is provided, its extreme pressure and anti-wear properties determined according to GOST on a four-ball friction machine increase.

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Viscosity improvement property of a lubricant additive is commonly attributed to polymer coil expansion with increasing temperature, although only some polymer chemistries show conformance to this conceptual mechanism. Herein, we show that the polarity of base oil governs whether this mechanism underlies the action of a viscosity modifier (VM) by combining experimental and computational studies. Poly(butyl methacrylate) (PBMA) dissolved in diethylene glycol diethyl ether (DGDE) or a mixture of DGDE (polar solvent) and squalane (SQ, nonpolar solvent) was used as a model lubricant oil system. Specific viscosity of the polymer solutions measured over a wide range of additive concentrations and temperatures revealed that thickening efficiency of the VM decreased with decreasing base oil polarity. While the VM counteracted temperature-induced thinning of the low polarity base oil, in the polar solvent, the polymer did not enhance the solution viscosity at higher temperatures. Aiming to unravel the molecular mechanism underlying viscosity improvement at elevated temperatures in the differe... Read More

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The key function of lubricants is to reduce the friction, wear, and heat between the parts that are in contact with each other. The main applications of the lubricants are to control temperature, and reduction in wear and corrosion of the machinery. Keeping in mind the importance of lubrication and its applications in varied machines. The goal of this research is to inspect the heat transmission impact in the magnetohydrodynamic flow of Jeffrey liquid near a stagnation point through a lubricated surface. Lubrication is accomplished by a shear-thinning liquid. The velocity, continuity, and shear stress, amalgamated with power-law fluids, are used to develop interfacial conditions. The exclusivity of the anticipated model is the inclusion of variable thermal conductivity and diffusion coefficients in the existence of homogeneous-heterogeneous reactions. Using the KellerBox finite-difference approximation approach, the numerical results are accomplished. The outcomes are portrayed and tabulated in the form of diagrams and tables, respectively. It is witnessed that a greater magnetic fi... Read More

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Viscosity-index improving agent for lubricating oils that provides improved low-temperature viscosity, high-temperature high-shear viscosity, and gelation index. The agent comprises a copolymer containing a polyolefin-based monomer, a C4-alkyl-substituted monomer, and at least one of a C2-C3-alkyl-substituted monomer or a C4-alkyl-substituted monomer, along with an ester oil. The copolymer is present in a range of 10-70 wt% and the ester oil in a range of 0.01-5 wt% of the total agent weight.

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<div class="section abstract"><div class="htmlview paragraph">The purpose of this study is to investigate how the kinematic viscosity of lubricating oil used in hybrid electric vehicle (HEV) and electric vehicles (EV) transaxles affects thermal conductivity and gear seizure resistance. This study investigated the relationship between viscosity, thermal conductivity and gear seizure resistance in detail and found that thermal conductivity tends to decrease with decreasing viscosity. It was also found that the thermal conductivity decreases significantly after a certain viscosity. The relationship between viscosity and gear seizure resistance was also investigated and it was found that too low a viscosity causes a significant deterioration in gear seizure resistance.</div></div>

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Grease composition for lubricating applications like gears that provides stable grease supply and retention. The grease has a base oil of polyalphaolefin (PAO) and a soap thickener. It has a viscosity transition stress of 300 Pa or more at 25°C to penetrate contact areas, but less than 40 Pa at 100°C to prevent grease migration. Shear viscosities at 25°C and 100°C are also optimized to balance grease supply and retention.

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Lubricants play a central role in many technical applications, e.g. in bearings and gears as well as in machining processes. In such applications, lubricants are exposed to extreme conditions in the contact area. In lubrication gaps, the pressure can reach values up to 5 GPa. The thermophysical properties of lubricants, and in particular the viscosity, at such extreme conditions have an important influence on the friction and wear behavior of a tribosystem. Accordingly, reliable lubricant property models are a prerequisite for accurate tribological simulations, e.g. elastohydrodynamic lubrication (EHL) simulations. Presently, the vast majority of experimental thermophysical property data are only available up to 1 GPa. Thus, reliable and robust models with strong extrapolation capabilities to higher pressure are required. In this work, viscosity measurements of squalane in a temperature range be tween 20 C and 100 C and pressures up to 1 GPa were carried out. Based on that data, a physical model for the viscosity was developed. The model is built by combining a molecular-based equa... Read More

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Reducing the viscosity of the lubricant is an effective way to improve the energy efficiency of automobiles. However, designing a lubricant with the desired properties requires elucidating the relationship between viscosity and molecular structure. In this study, we measured the temperature dependence of the dielectric relaxation of model lubricants with different molecular structures. Dielectric relaxation measurements were used to evaluate the influence of ambient viscosity on the motility of single molecules. In addition, we measured the temperature dependence of the lubricant viscosity using a rotational viscometer. By comparing the flow viscosity and dielectric relaxation measurement results, we showed that the activation volume and energy of the luburicant, which determine viscosity, can be resolved. As a result, we succeeded in quantitatively evaluating the contribution of molecular structure to changes in the activation energy, and elucidated the effect of the density of polar groups per molecule on changes in the activation volume.

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The relation with viscosity and pressure of lubricant has been considered in detail from the past. Barus equation that was presented in 1893 is known as the basic equation. This paper describes the new linear viscosity equation, that included dimensionless density and temperature other than pressure as functions in comparison with Barus equation. Author measured high pressure viscosity by using reciprocating-piston type test apparatus and measured high pressure density by using capacity type test apparatus in each temperature and pressure. After that, author attempted to derive the density into Barus equation and it was found that dimensionless density was preferable as density. Furthermore, author attempted to introduce temperature into Barus equation. It became able to in this way deal with the new viscosity equation as a linear equation. It found out that the logarithm of dimensionless viscosity was proportional to pressure and it was inversely proportional to temperature and dimensionless density cubed. And it was found that these slope of lubricants by this linear equation are... Read More

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Lubricant has an important function in protecting the parts of an engine where to minimise the wear formation on the surface between two moving parts. The mixing of lube oil SAE10W-30 Petronas oil and Shell oil may have caused an effect to the wear stability of the lubricant. The aim of this study is to determine the behaviour of the oils viscosity, COF and WSD of the ball using the FBM. The experiment was done under different speed and the mixture was rested. Based on the analysis, the viscosity is thinning as the temperature gets high. The thinnest oil is 20% Shell mixture and 5% Shell is the thickest but viscosity was not affected by the rested time. COF has decreased as the speed increased. However, longer resting period did not give any effect as the speed higher but has increased COF. The WSD was increased by the higher concentration of Shell as well as the speed. Overall, different concentration of Shell oil and rested time has an effect on the lubricity performance.

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The paper concerns selected aspects of the application of coolinglubricating agents as well as methods and devices assigned to lubrication in hot die forging processes realized at elevated and high temperatures in the context of their effect on the quality of the forgings and the durability of the forging instrumentation. An analysis was made of the currently used lubricants and their properties and applications in selected industrial forging processes, and a review was conducted of the presently applied coolinglubricating systems and devices. The article also presents the authors own studies referring to the effect of the application of lubricating and cooling agents, the volume of the lubricant portion, the times and directions of its application, and other factors affecting tribological conditions. It also presents lubricating devices constructed based on the knowledge and experience of the authors. The elaborated systems, introduced into selected forging processes, make it possible to examine the effect of the volume and time-frequency of the applied lubricant dose on the wear... Read More

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In an oil-film lubricating system, fit clearance and the different types of lubricating oil can result in changes in the orbit of shaft center, thereby affecting the stability of the system. Subject of this paper is the camshaft lubricating system of airspace engine, to figure out the effects of fit clearance and the type of lubricating oil on the shaft center orbit of camshaft, in this study, a 3D model of the camshaft lubricating system was built for simulation purpose based on Reynolds equation, and the calculation results suggest that, as the fit clearance grows larger, the convergence position of shaft center gradually moves away from the starting position, and the stability of shaft center declines; in terms of the type of lubricating oil, the higher the viscosity of the lubricating oil, the closer of the position of shaft center to the starting point, and the higher the stability. Our research method can be applied to common oil-film lubricating systems and we hope it could provide a theoretical evidence for the selection of fit clearance and type of lubricating oil for such s... Read More

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Synthetic esters are used as lubricants for applications at high temperatures, but their development can be a trial and error process. In this context, molecular dynamics simulations could be used as a tool to investigate the properties of new lubricants, in particular viscosity. We employ nonequilibrium molecular dynamics (NEMD) simulations to predict bulk Newtonian viscosities of a set of mixtures of two esters, di(2-ethylhexyl) sebacate (DEHS) and di(2-ethylhexyl) adipate (DEHA) at 293 and 343 K as well as equilibrium molecular dynamics (EMD) and NEMD at 393 K and compare these to experimental measurements. The simulations predict mixture densities within 5% of the experimental values, and we are able to retrieve between 99% and 75% of the experimental viscosities for all ranges of temperature. Experimental viscosities show a linear trend which we are able to capture using NEMD at low temperature and EMD at high temperature. Our work shows that, using EMD and NEMD simulations, and the workflows we developed, we can obtain reliable estimates of the viscosities of mixtures of indust... Read More

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Abstract The use of lubricants is commonplace when drilling with water-based drilling fluids. They are less frequently applied when drilling with non-aqueous fluids, as the oil-based drilling fluid is thought to impart a high lubricity. With increased reach of the wells, lubricants are also applied in non-aqueous fluids (NAF) to reduce torque and drag at high angle, for extended reach and horizontal wells to improve drilling efficiency. However, the performance of these lubricants in NAF at extended periods of elevated temperature at downhole conditions is often inconsistent, thought to be hampered by ineffective metal binding and hydrolytic instability of the lubricant molecule. This requires frequent re-dosing and therefore higher cost to maintain performance. In order to identify a better-performing lubricant, it was necessary to better understand the fundamentals of lubrication in a drilling fluid. For example, what portion of the well contributes most to torque and drag? What is the frictional regime that dominates the lubricity between a drill pipe and its contact points? Looki... Read More

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The replacement of conventional lubricants with esters is an alternative to provide a low environmental impact and at the same time excellent lubricity features, the high solubility of additives, good viscosity index, low volatility, and high thermal stability. Friction modifiers and antiwear/extreme pressure additives are extensively used to save energy and increase operational life in machine components. In this study, the lubricity of a Group IV base oil containing ester and various benchmark friction modifiers and/or antiwear/extreme pressure additives is measured to evaluate the influence of the ester on the tribological performance of the mixture components. The tribological performance is discussed based on the tabulation of the traction coefficient using a Mini-Traction-Machine and on the measurement of the specific wear rate from the wear scar of the experimental studies using an optical profilometer. In general, results show synergies between the ester and the additive formulations, reducing the wear rate to 75% and decreasing the traction coefficient a 20 to 50%, depending... Read More

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Reducing lubricant viscosity is one effective way to improve the energy efficiency of automobiles. Designing a lubricant with the desired properties requires elucidating the relation between viscosity and molecule structure. In this study, we measured the temperature dependence of dielectric relaxation for lubricants with different molecular structures. The dielectric relaxation measurements can evaluate the motility of single molecules influenced by the ambient viscosity. Additionally, we measured the temperature dependence of lubricant viscosity with a rotational viscometer. By comparing the results of both flow viscosity and dielectric relaxation measurements, we find a correlation between flow activation energy and single-molecule mobility when viscosity is dependent on molecular weight, while there is no correlation between them when polarity dominantly affects viscosity.

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In this chapter, we give the basic equations, numerical calculation method and program of one-dimensional and two-dimensional thermal hydrodynamic lubrication of non-Newtonian fluids. In these programs, viscosity of lubricant varying with temperature, and pressure is considered. However, for simplicity, we only consider the variation of viscosity of lubricant in the flow direction, but not in the film thickness direction. Furthermore, density of lubricant is also considered independent of pressure and temperature. Some examples are presented.

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In the previous chapters, we do not consider the variation of temperature. In some cases of hydrodynamic lubrication, such as elastrohydrodynamic lubrication (EHL), temperature rise may be obvious so that it is necessary to consider temperature variation, that is, thermal hydrodynamic lubrication (THL). In this chapter, the energy equation is introduced first. Due to the existence of temperature, the viscosity and density of lubricant will change both in the film thickness direction and in the flow direction. Therefore, the calculation process is very complicated. We give the basic equations and calculation methods of THL of non-Newtonian fluids. Then, we solve one-dimensional and two-dimensional THL problems of non-Newtonian fluids with the separated flow velocity method. Some examples are presented.

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In recent years, the demand for friction reduction in oil lubrication systems has become increasingly important due to the need to improve fuel economy and achieve carbon neutrality. Ester-based lubricants are known to show low friction and environmentally friendly, and they have high viscosity indexes. In the present paper, first, in situ reflectance spectroscopy was used to clarify the behavior of the oil-film thickness increase during sliding. The results showed that as the number of ester bonds increased from 1 to 4, the ester oil film thickened and the friction coefficient decreased from 0.10 to 0.06. In addition, oleic-acid-type lubricants were found to have superior ability to form a thicker oil film than the isostearic acid type.

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Temperature primarily influences thermal elastohydrodynamic lubrication (TEHL) through the temperature dependence of the viscosity of the liquid. The pressure and temperature dependences of viscosity increase rapidly as the glassy state is approached from the liquid state, a property known as fragility. The glass temperature increases with pressure and reaches to ordinary temperatures at TEHL pressures. Most TEHL analyses have ignored fragility by utilizing a viscosity correlation incapable of describing this behavior. Here, a low-viscosity, fragile oil is characterized for low-shear viscosity to 1.6 GPa and TEHL line contact simulations show, not only a substantial effect on friction, but also significant differences in minimum film thickness when fragility is not ignored, as is customary in classical TEHL. The influence on friction manifests even under moderate load and speed conditions, while that on film thickness seems to be restricted to high loads.

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In modern internal combustion engines, the lubricant viscosity affects greatly the friction power loss. To obtain maximum fuel economy of the engines, the lubricants with different viscosities are considered to evaluate the friction properties of the compression ring-cylinder liner conjunction in the engines in this study. To conduct the evaluation, an improved mixed lubrication model is developed with considerations of the cylinder liner deformation, the lubricant thermal effect & transportation, and the change of lubrication condition from full flooded to starve. On this basis, the influence of different viscosity lubricants on the minimum oil film thickness, friction, power loss, FMEP, and wear load are investigated. The numerical result indicates that the low viscosity lubricant is more beneficial to facilitate the change of lubrication condition from starve to fully flooded. Furthermore, the low viscosity lubricant will result in large wear load on the compression ring surface while reducing the friction power loss.

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Lubrication is a crucial factor in improving the tribological performance of various components and thus, the overall working performance of an internal combustion engine. This paper addresses the lubrication performance of different lubricants, which are commercially available and used in automobile engines. The experiments are conducted on a four-ball tester for evaluating the tribological performance of selected lubricants, namely SAE20W-50, SAE15W-40, and SAE10W-30. The tests are designed according to ASTM D4172, and the friction and wear performance of the lubricants are characterized for better lubrication performance. The lubricant SAE15W-40 has shown excellent lubrication performance with lower friction coefficient and wear scar diameter among all the tested lubricants.

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Polymer additives in lubrication oils are known to play a role as viscosity index improvers that change the temperature dependence of viscosity. On the other hand, it is assumed that polymers adsorbed on surfaces contribute to low friction, and clarification of their mechanical properties and temperature dependence is essential for lubrication design. In our previous research, we have successfully measured the gap dependence of mechanical properties (shear viscoelasticity) of base oils by applying the fiber wobbling method (FWM), a nano-rheological measurement method that we originally developed. In this study, we developed a temperature-control stage for FWM to measure the temperature dependence of shear viscoelasticity in nano-gaps of polymer-added lubricants.

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The relative viscosity, specific viscosity and reduced viscosity were enumerated to evaluate the intrinsic viscosity for three types of base lubricating oils 40, 60 and 150 stock that were mixed with olefin copolymer of type Polyvinyl chloride-100XA at four temperature degrees of 40, 60, 80 and 100 oC and using of three different kinds of polymeric additives formulations named as Lubrizol 21001, HiTEC 8722B and HiTEC 340. Mixtures of base lubricating oils with proportions of 2, 4, 6, 8 and 10 wt% from the Polyvinyl chloride-100XA were blended with 4 and 8 wt% of the three additives. The results were remarkable and showed that the intrinsic viscosity for the base lubricating oils increase by increasing both temperature degrees and the proportions of Polyvinyl chloride-100XA and the additives.

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Solid lubricant WS2 was encapsulated in the dimples on the cylinder surface by the hot-pressing method. The tribological and releasing performance of the as-prepared sample were investigated under high temperature conditions. The results indicate that, compared with the original cylinder, WS2 in the dimples exhibited better tribological properties at high temperature than at room temperature. The average friction coefficients of the as-prepared samples were about 0.13 and 0.15 at high temperature and room temperature, respectively, which were 27.8% and 16.7% lower than that of the original cylinder, respectively. Moreover, compared with the original cylinder, the anti-adhesion time of the as-prepared sample increased 2.3-fold. Additionally, the reduced viscosity of the lubricating oil caused by high temperature accelerated the erosion effect and release rate of the solid lubricant in the dimples. Thus, the polar additives in the lubricating oil and the chemical reactions between the cylinder substrates and solid lubricants that WS2 released from the dimples are the main factors in fr... Read More

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The Walther equation is often used for the viscosity temperature characteristics of lubricants. However, it was found that it cannot be applied to high pressure viscosity. In this study, the relationship between viscosity, temperature and pressure was analyzed. As a result, viscosity at each pressure was found to be negatively proportional to the square of temperature, and linear equations converges at absolute zero were derived. In parallel, a thought experiment was conducted on the viscosity of ideal liquid. It was found that the absolute zero viscosity (t=0) of ideal liquid is constant regardless of the pressure. This is consistent with the convergence point at absolute zero of the linear equation in the above analysis. Furthermore, a high pressure viscosity temperature linear equation incorporating the pressure was derived. This eqaution is a van der Waals type viscosity equation consisting of three intrinsic constants: absolute zero viscosity t=0 [mPas], viscosity constant 1/B [GPa/K2] and pressure constant C/B [GPa]. It was found that this is liquid viscosity equation. This ... Read More

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This reprint focuses on the hot issue of bearing lubrication and thermal analysis, and brings together many cutting-edge studies, such as bearing multi-body dynamics, bearing tribology, new lubrication and heat dissipation structures, bearing self-lubricating materials, thermal analysis of bearing assembly process, bearing service state prediction, etc. The purpose of this reprint is to explore recent developments in bearing thermal mechanisms and lubrication technology, as well as the impact of bearing operating parameters on their lubrication performance and thermal behavior.

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Purpose This paper aims to address the influence of lubrication methods on operational characteristics, power losses and temperature behavior of gears and bearings. It contributes to the improvement of resource and energy efficiency of geared transmissions. Design/methodology/approach Experimental investigations were performed at a gear and bearing power loss test rig. Thereby, dip lubrication, injection lubrication with injection volumes from 0.05 to 2.00 l/min and minimum quantity (MQ) lubrication with an injection volume as little as 28 ml/h were considered. Measurements were evaluated in terms of no-load and load-dependent power loss, bulk temperatures and mean gear coefficients of friction. Findings Results show strongly reduced no-load gear and bearing losses for lubrication methods with low lubricant quantities. Load-dependent losses are similar to conventional lubrication methods and tend to be lower at high speed. This is related to higher bulk temperatures, as the heat dissipation of lubrication methods with low oil quantities is limited. Limited thermal load limits were sh... Read More

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Motor oils provide lubricating, thermal control, detergent, sealing, and anti-corrosion properties.These are all provided by motor oil.Many factors act on the lubricating oil while the engine is running, including high temperatures, fuel entering.The study of the processes of oil aging and mechanical impurity dispersion is critical for extending the engine's service life.lubrication temperature, the lubrication system, oxygen contained in the air, and foreign impurities.The oil's properties change as a result of the numerous physical and chemical processes that it goes through: the oil "ages" [1].It darkens during operation, changes in viscosity, flash point, acidity change, molecular

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Lubricants predominantly used to reduce friction and gain smooth functioning of a vehicle. Biodegradable lubricants are perceived to be alternative to mineral oil lubricants because of their properties and biodegradability. This review paper discusses the effect of biodegradable lubrication in term of emission performance, wear, friction and viscosity effect to the internal combustion engine using multiple types of biodegradable lubrications. Bench wear test was conducted using Yamaha, ET 950 to carry out the effect of the biolubricant in spark ignition (SI) engine. The bench test was conducted under several conditions: pressure, 3.0 MPa; sliding speed, 0.20 m/s; sliding stroke, 80 mm; room temperature, >25C. The second experiment were conducted with 100 percentage SAE 40, palm oil and palm oil (14%) + castor oil (86%) blend as its crankcase lubricant using four stroke compression ignition (CI) engine. A thermocouple was used to measure the parameters temperature every 5 minutes interval with the engine operating for an hour under no load, 2.5 kg, 5 kg, and 7 kg load condition. T... Read More

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Castor oil is an environment-friendly lubricant with good biodegradability and renewable behavior. However, castor oil as a green lubricant has a few shortcomings, such as a low viscosity index and low oxidative stability due to the presence of unsaturated bonds. The temperature affects the lubrication performance of castor oil. In the present study, the lubrication performance and viscosity behavior of castor oil lubricating the friction pair of a steel ball and a nickeltitanium (NiTi) alloy disk were systematically investigated under different temperatures. The results show that the lubrication performance of castor oil is influenced by temperature due to the fact that the viscosity of castor oil varies with the temperature. The coefficient of friction (CoF) of castor oil is as super-low as 0.076 at a temperature of 40C, but is relatively high at other temperatures. The factors affecting the lubrication performance were investigated, and a possible antifriction mechanism is proposed in this study.

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Lubrication is an important thing in ship machining operations because it becomes a protective layer to separate two surfaces that are in contact with each other with three phases of objects whose volume remains at a constant temperature and pressure. Lubrication serves to prevent friction between components so that it becomes smoother. If the engine is at a high temperature, the oil viscosity will tend to decrease. The more often the lubricant is used, the thing that happens is that the temperature of the lubricating oil varies. The purpose of this study is to describe the behavior of the lubrication temperature on the ship. The research uses quantitative methods by observing the temperature of the main engine along the way by looking at indicators and direct measurements on the main engine using a thermocouple. The results showed that the temperature behavior is very dependent on the age of the lubrication and the operation of the cooling system on the ship's machining system. This study concludes that the lubrication temperature behavior is very dynamic and the influencing factors... Read More

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As low-viscosity oil is used more widely to reduce friction losses in IC engines, concerns are growing about an increase in friction, wear and scuffing at the sliding surfaces on tribo-components. The authors conducted an analytical study on thermal friction characteristics of boundary lubrication based on the physical and chemical properties of interface materials and lubricants. The study was intended to investigate the effect of temperature on the function of oil additives as a friction modifier and/or anti-scuffing agent. Three low viscosity base oils, three extreme pressure and anti-wear agents and two organo-molybdenum friction modifiers were used to measure friction changes with a cam/follower test apparatus. The authors analyzed a relationship between friction and temperature in the running-in process of interfaces in consideration of the functional sensitivity of additives in low-viscosity oils. This analysis was focused on physicochemical properties on the basis that the oil viscosity, the adsorption of oil molecules, the chemical reaction of oil additives that forms a trib... Read More

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High-temperature lubrication is widely used in modern industrial fields such as aviation, aerospace, nuclear, metallurgy and metal processing. The service temperature of corresponding mechanical equipment is getting higher and higher, and the problems of high-temperature lubrication and wear failure are becoming more and more prominent.This article reviews the latest research progress of binary and ternary oxide coatings with high-temperature solid lubricant application potential, discusses the structure, chemical and electrical properties of these oxides and their tribology, and focuses on the main types of solid lubricating materials. The correlation of performance and its lubrication mechanism are analyzed.This review also discusses the industrial applications of these coatings and predicts that lubricating coatings might develop in the direction of self-lubricating and self-healing smart lubricating materials.

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Abstract The molecular structure of lubricating oil affects its lubrication properties, catalytic and hydrolytic stability, and anti-wear properties. Based on the idea of material genomics, researchers are trying to find the correlation between structural characteristics and functional performances of lubricating oil, but the correlation can only explore the influence weight of structural parameters on performance, it is also very important to research the influence mechanism. In this study, through quantum mechanics/molecular mechanics calculations, (i) the spatial configurations of four typical ester lubricants with different chain length structures were studied, (ii) effects of active functional groups and charge distribution on the properties of the ester lubricants were discussed, and (iii) electronic transition and molecular orbital contributions were compared. The calculated results are expected to provide considerable support for theoretical research on the anti-wear and anti-oxidation mechanisms of ester lubricants and assist the rapid design, development and application of ... Read More

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It is a well-known fact that the consumption of conventional cutting fluids in metalworking industries leads to severe health and environmental issues. Owing to the EPA (Environmental Protection Agency) increasing regulations regarding pollution and contamination, there is a dire need for a greener fluid with excellent cooling and lubrication characteristics to diminish the environmental impact of cutting fluids, as well as to improve machinability. Cryogens are greener and excellent coolants but poor lubricants, while ester oils are excellent lubricants and poor coolants. Therefore, a hybrid lubri-coolant cutting fluid with synergistic cooling and lubrication characteristics could be a desideratum to replace conventional cutting fluid. To investigate a newly proposed hybrid lubri-coolant, thermophysical properties (density, thermal conductivity, specific heat, and viscosity), heat transfer properties (surface temperature, heat flux, and heat transfer coefficient), and machinability properties (tool life, etc.) are key characteristics of the fluids that decide phase change and heat d... Read More

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A lubricating oil composition for automobile transmissions that achieves excellent shear stability, temperature viscosity properties, and low-temperature viscosity properties. The composition comprises a lubricant base oil and a liquid random copolymer of ethylene and α-olefin prepared by solution polymerization under a specific catalyst system. The copolymer has a molecular weight distribution that balances shear stability with temperature viscosity properties, enabling the composition to maintain its viscosity and lubricating performance over a wide temperature range.

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The molecular arrangement in the lubricating film will affect the friction coefficient. When using liquid crystal as a lubricant, various methods can be tried to adjust the arrangement of the liquid crystal molecules to actively control the lubrication effect. In this study, 5CB with a clearing point of 35C was used as a lubricant. By changing the temperature, the lubricating molecules in the contact area were switched between an ordered liquid crystal state and a disordered liquid state, and a friction coefficient that changed synchronously with the temperature was obtained. It provides new ideas for active control of lubrication in the fields of smart bearings and emergency braking.

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Background: The dynamic viscosity - temperature characteristics of lubricants are the main factors used to determine the oil film thickness and carrying capacity. There are few studies on the factors affecting the dynamic viscosity-temperature characteristics of lubricating oils and the dynamic viscosity-temperature model. Objective: This research aims to analyse the influences of lubricating oil type and initial kinematic viscosity on dynamic viscosity - temperature characteristics and present a new dynamic viscosity - temperature model. Methods: The characteristic curves of dynamic viscosity versus temperature of polyol ester oil, paraffinic mineral oil, and five types of PAO (poly a-olefin) oils with different initial viscosities were obtained by using a kinematic viscosity test device and a density test device. The influences of lubricating oil type and lubricating oil viscosity on dynamic viscosity - temperature characteristics were analysed. Based on our patent technology and repeated verification, a new dynamic viscosity - temperature model was presented. Results: Viscosity - ... Read More

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Viscosity is the most important lubricant parameter as lubricant requires suitable values to ensure its performance in industrial applications under a high pressure and temperature. In this study, the effects of viscosity on temperature for engine oil (SAE 20W40) and palm oil were studied in journal bearing application using the ANSYS FLUENT CFD (computational fluid dynamic) method. In addition, this study also compared the effects of constant viscosity and viscosities that dependent on temperature for engine oil (SAE 20W40) for an application of journal bearing at a different rotational speed of journal bearing start from 200 rpm, 400 rpm, 600 rpm, 800 rpm, and 1000 rpm. The results show that the pressure distribution in journal bearing is in agreement with the experiment by using the correct method in ANSYS FLUENT. Finally, under the hydrodynamic lubrication regime, the lubricant viscosity has a significant impact on the improvement of a journal bearings most essential aspects (maximum pressure and load carrying capacity). Hence decision to consider constant viscosity conditions o... Read More

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