Research

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9 pages, 1551 KiB

Open AccessArticle

The Influence of a Piston Ring Coating on the Wear and Friction Generated during Linear Oscillation

by Arthur Rozario, Christoph Baumann and Raj Shah

Lubricants 2019, 7(1), 8; https://doi.org/10.3390/lubricants7010008 - 14 Jan 2019

Cited by 9 | Viewed by 3989

The piston group is responsible for contributing to ~50% of the frictional losses of an engine, which ultimately leads to the waste of fuel. This coupled with the fact that gasoline is a finite resource linked to CO₂-emissions, there is an [...] Read more.

The piston group is responsible for contributing to ~50% of the frictional losses of an engine, which ultimately leads to the waste of fuel. This coupled with the fact that gasoline is a finite resource linked to CO₂-emissions, there is an increased demand of higher performance vehicles, which coincidently further loads the piston ring. As of yet, there are plenty of studies that already study the piston ring’s contact with the cylinder liner. However, this study focuses on a cost-effective Schwing, Reib, Verschleiss (SRV) instrumentation that allows to pre-screen lubricants, additives, materials and coatings for their friction, wear and load carrying capacity including scuffing resistance. As a result of the pre-screening conducted outside of engine by using the SRV instrument, it brings us to the following conclusion: the PVD CrN-TiN 1º Group coating on the piston ring produces the least wear, as well as the lowest coefficient of friction. Moreover, it is concluded that a coating that is based from CrN and TiN allows the piston ring to perform better in engine settings. A continued understanding of the piston-cylinder-contact assembly only helps engineers, scientists and any other stakeholder to improve on the piston ring and cylinder liner interaction. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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12 pages, 2554 KiB

Open AccessArticle

The Effect of Agglomeration Reduction on the Tribological Behavior of WS₂ and MoS₂ Nanoparticle Additives in the Boundary Lubrication Regime

by Yosef Jazaa, Tian Lan, Sonal Padalkar and Sriram Sundararajan

Lubricants 2018, 6(4), 106; https://doi.org/10.3390/lubricants6040106 - 10 Dec 2018

Cited by 14 | Viewed by 3769

Abstract

This study investigates the impact of different surfactants and dispersion techniques on the friction and wear behavior of WS₂ and MoS₂ nanoparticles additives in a Polyalphaolefin (PAO) base oil under boundary lubrication conditions. The nanoparticles were dispersed using Oleic acid (OA) [...] Read more.

This study investigates the impact of different surfactants and dispersion techniques on the friction and wear behavior of WS₂ and MoS₂ nanoparticles additives in a Polyalphaolefin (PAO) base oil under boundary lubrication conditions. The nanoparticles were dispersed using Oleic acid (OA) and Polyvinylpyrrolidone (PVP) to investigate their impact on particle agglomeration. The size distribution of the dispersed nanoparticles in PAO was measured by dynamic light scattering. The nanoparticles treated using PVP resulted in the most stable particle size. Friction studies showed that nanoparticle agglomeration reduction and the homogeneity of the suspension did not significantly impact the friction reduction behavior of the lubricant. Reciprocating wear experiments showed that, for our test conditions, both WS₂ and MoS₂ nano additives exhibited maximum wear depth reduction (45%) when using the PVP surface treatment compared to base oil. The wear results confirmed the significance of minimizing agglomeration and promoting high dispersion in promoting favorable wear resistance under boundary lubricant conditions. Analysis of the wear surfaces showed that a tribofilm formation was the primary wear reduction mechanism for WS₂ particles treated by PVP while, in the case of MoS₂ treated by PVP, the mechanism was load sharing via particles rolling and/or sliding at the interface. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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11 pages, 4687 KiB

Open AccessArticle

Impact of Fuel Contents on Tribological Performance of PAO Base Oil and ZDDP

by Yan Zhou, Weimin Li, Benjamin C. Stump, Raynella M. Connatser, Sladjan Lazarevic and Jun Qu

Lubricants 2018, 6(3), 79; https://doi.org/10.3390/lubricants6030079 - 07 Sep 2018

Cited by 8 | Viewed by 4570

Abstract

Fuel and water contents are inevitable in automotive engine oils. This study intends to investigate the impact of the addition of gasoline (3–20%) and water (1%) on the lubricating performance of synthetic base oil (PAO), with or without an anti-wear additive (ZDDP), for [...] Read more.

Fuel and water contents are inevitable in automotive engine oils. This study intends to investigate the impact of the addition of gasoline (3–20%) and water (1%) on the lubricating performance of synthetic base oil (PAO), with or without an anti-wear additive (ZDDP), for a steel-cast iron contact. Fuel-added PAO showed an increase in the load carrying capacity. Oil electrical conductivity and total acid number (TAN) measurements showed slightly increased conductivity and marginally increased acidity at a higher fuel concentration. In contrast, an increased wear rate, proportional to the fuel concentration, was observed in a prolonged test with constant-loading. Results suggested that the fuel addition is a double-edged sword: reducing the scuffing risk by providing stronger surface adsorption and increasing the sliding wear rate by bringing down the oil viscosity. The PAO-water blend formed an emulsion and resulted in a significantly increased load-carrying capacity, again likely due to the higher polarity and possibly acidity. For the ZDDP-containing PAO, the addition of 1% water and 3% fuel generated 24% and 52% higher wear. The phosphate polymerization level was reduced on the worn surfaces by the introduction of water but the thickness of ZDDP tribofilm was not significantly affected. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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9 pages, 1223 KiB

Open AccessArticle

PAO Contributions to Energy Efficiency in 0W-20 Passenger Car Engine Oils

by Ken Hope

Lubricants 2018, 6(3), 73; https://doi.org/10.3390/lubricants6030073 - 22 Aug 2018

Cited by 11 | Viewed by 7454

Abstract

Energy efficiency improvements continue to be a significant challenge to the transportation and lubricant industries. Many areas are being examined to increase energy efficiency in lubricants. This paper examines contributions from base oils in terms of friction reduction since friction reduction is related [...] Read more.

Energy efficiency improvements continue to be a significant challenge to the transportation and lubricant industries. Many areas are being examined to increase energy efficiency in lubricants. This paper examines contributions from base oils in terms of friction reduction since friction reduction is related to energy consumption. The impact of base oil on the frictional differences in a passenger car lubricant is studied using PAO and Group III base oils. Chemical and physical property differences are highlighted and the Stribeck and Traction curves have been measured using a Mini Traction Machine (MTM). Relating the differences in friction to the energy efficiency have been estimated based upon different lubrication regimes measured with the MTM. Reductions in energy losses due to cooling or exhaust have not been included so that any improvements are estimated on frictional differences alone. These frictional improvements are assumed to be related to the differences in chemical make-up of the base oils studied. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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7 pages, 1373 KiB

Open AccessArticle

Reducing Friction with a Liquid Film on the Body Surface

by Nikolay Klyuev, Konstantin Polyakov and Alyona Krutovertseva

Lubricants 2018, 6(1), 25; https://doi.org/10.3390/lubricants6010025 - 07 Mar 2018

Viewed by 3649

Abstract

A flow of a thin layer of liquid is simulated on a flat surface of a body located in a stream of air. Liquid film on the surface of the body reduces frictional resistance and can be used as a boundary layer control [...] Read more.

A flow of a thin layer of liquid is simulated on a flat surface of a body located in a stream of air. Liquid film on the surface of the body reduces frictional resistance and can be used as a boundary layer control element. The paper presents a mathematical model of the film flow on a half-plane, located at an angle to the horizon. The fluid flow is determined by the force of gravity and friction from the external air current. A model of an incompressible viscous fluid is used in the boundary-layer approximation. The terms of the motion equation are averaged over the film thickness according to the Leibniz rule. In the cross section of the film, a quadratic law is adopted for the distribution of the longitudinal velocity, taking into account friction on the film surface. An analytical solution of the problem is obtained in the form of series in powers of the small parameter for determining the film thickness and the average longitudinal velocity along the length of the plate. It is shown that the friction decreases with flow around a half-plane with a film of liquid on the surface. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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Review

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26 pages, 5202 KiB

Open AccessReview

Effect of Humidity on Friction and Wear—A Critical Review

by Zhe Chen, Xin He, Chen Xiao and Seong H. Kim

Lubricants 2018, 6(3), 74; https://doi.org/10.3390/lubricants6030074 - 22 Aug 2018

Cited by 103 | Viewed by 10698

Abstract

The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity [...] Read more.

The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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14 pages, 2093 KiB

Open AccessReview

Opportunities and Challenges with Polyalkylene Glycol for Engine Oil Application

by Arup Gangopadhyay and John Cuthbert

Lubricants 2018, 6(3), 72; https://doi.org/10.3390/lubricants6030072 - 21 Aug 2018

Cited by 7 | Viewed by 4712

Abstract

Base oil plays an important role in engine oil formulation in delivering overall performance attributes in addition to additives. Non-traditional base oil like polyalkylene glycol (PAG) did not get much attention in the past for formulating automotive engine oil. This investigation explored PAGs [...] Read more.

Base oil plays an important role in engine oil formulation in delivering overall performance attributes in addition to additives. Non-traditional base oil like polyalkylene glycol (PAG) did not get much attention in the past for formulating automotive engine oil. This investigation explored PAGs for enhancing engine oil performance primarily for fuel economy benefit over traditional mineral oil-based formulations. This paper highlights key findings from an extensive investigation, parts of which were published in detail elsewhere, and identifying opportunities and challenges. Several PAG chemistries were investigated depending on their feedstock material. Friction performance was evaluated by several methods starting with laboratory bench tests to engine components to chassis roll dynamometer tests. Durability was also evaluated from laboratory bench tests to engine components to ASTM sequence tests. The investigation revealed that significant friction reduction or fuel economy gain can be achieved with PAG oil but wear protection capability, piston deposit, and varnish require much improvement requiring identification/development of additive components. A few alternative routes for performance improvement are suggested. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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15 pages, 1927 KiB

Open AccessReview

Common Properties of Lubricants that Affect Vehicle Fuel Efficiency: A North American Historical Perspective

by Mark T. Devlin

Lubricants 2018, 6(3), 68; https://doi.org/10.3390/lubricants6030068 - 03 Aug 2018

Cited by 23 | Viewed by 6620

Abstract

The development of advanced lubricants to improve vehicle fuel efficiency can appear to be as simple as lowering the viscosity and frictional properties of a fluid. However, applied research studies have shown that it is quite difficult to quantify the fuel efficiency properties [...] Read more.

The development of advanced lubricants to improve vehicle fuel efficiency can appear to be as simple as lowering the viscosity and frictional properties of a fluid. However, applied research studies have shown that it is quite difficult to quantify the fuel efficiency properties of advanced lubricants in vehicles. A review of the historical research predominantly performed in North America in this area reveals that there are many factors to consider in order to demonstrate the effectiveness of advanced lubricants. First, the methodology used to measure vehicle fuel efficiency will impact the results since there are many factors not related to the lubricant which will influence vehicle fuel efficiency. Second, developing advanced fuel-efficient lubricants under well controlled conditions overlooks the issue that lubricant properties such as viscosity and friction affect the operating conditions encountered by the lubricant in the vehicle. Finally, the physical properties of lubricants that historically control fuel economy do not have the same effect on fuel efficiency in all vehicles. The proper vehicle or system level test needs to be selected to properly assess the benefits of new advanced lubricants. Full article

(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)

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