Friction-reducing Performance Research Articles

Effects of wall thermal state on the cooling and friction reduction characters for supersonic film using gaseous hydrocarbon fuel

• The region influenced by the wall thermal state is limited within 1 mm off the wall. • Increase of the wall cooling heat flux improves the hydrocarbon film cooling performance. • The cooling enhancement can be equivalent to an additional wall heat flux of −0.36 MW/m 2 . • Increase of the wall cooling heat flux is unfavorable for reducing skin friction. Film cooling using gaseous hydrocarbon fuel is an effective way to meet the thermal protection and friction reduction demands of hydrocarbon-fueled scramjet engines. The cooling and friction reduction characteristics of the hydrocarbon film can be influenced by the wall thermal state through the variation of endothermic and exothermic chemical reactions in the film. Numerical investigations based on the RANS method have been performed to evaluate the effects of the wall thermal state on the hydrocarbon slot film cooling performance. Four wall thermal states which represent different regenerative cooling levels are simulated. Results show that an increase of the wall cooling heat flux is beneficial to the film cooling performance while has unfavorable effects on the film friction reduction performance. Further analysis reveals that the net energy effects of the chemistry in the hydrocarbon film can be equivalent to an additional constant wall cooling heat flux of −0.36 MW/m 2 within a certain range. Besides, the proportion of this equivalent wall cooling heat flux in the total wall cooling heat flux decreases from 100% to 26% for different wall thermal states. Therefore, the cooling enhancement brought by the endothermic chemistry is comparable to the regenerative cooling. However, the wall shear stress is less sensitive to the wall thermal state. The maximum deviation of the total wall friction for different wall thermal states is less than 8% compared to the reference value.

Effect of Molecular Weight on Tribological Properties of Polyether Amine Derivatives under Different Contact Modes

The requirements for the fuel economy of modern industry continue to drive the progress of low-viscosity lubricants. The present work reports the application of polyether amine derivatives as friction modifiers to improve the tribological properties of low viscosity poly-alpha-olefin. Three polyether amine derivatives with different molecular weights were synthesized, the tribological properties of which were systematically investigated under three different contact modes. These functionalized polymers exhibited significant friction reduction and wear resistance properties in the point-on-flat and line-on-flat friction tests, but just showed anti-wear performance in the severe point-to-point contact mode. The results exhibited that molecular weights of the polymers had a direct effect on their tribological properties. The increase of molecular weight in a certain range was beneficial to the improvement of tribological properties, but further undue increase will rather reduce the friction reduction and wear resistance performances. It can be indicated that the number of oxygen atoms increased with the molecular weight of the polymer, which will be conductive to the adsorption of the polymer on the metal surface. However, when the molecular weight of the polymer exceeds a certain value, the steric hindrance of the molecules adsorbing to the metal surface increases, which in turn has a negative impact on the tribological properties.

One-step green synthesis of oil-dispersible carbonized polymer dots as eco-friendly lubricant additives with superior dispersibility, lubricity, and durability

Chemical functionalization provides effective protocols for inorganic nanomaterials as oil-dispersible lubricant additives. Nevertheless, harsh reaction conditions and arduous post-processing are frequently encountered when adopting this approach. Herein, four types of carbonized polymer dots (CPDs) with admirable dispersibility and long-term stability (more than 6 months without any sediments) in polyethylene glycol (PEG200) were synthesized by a one-step and green solvothermal route using saccharides as the single precursors. The tribological behaviors of CPDs as the lubricant additives of PEG200 were systematically evaluated and compared, confirming that the anti-wear and friction-reducing performances of PEG200 can be effectively enhanced after blended with CPDs. Clarified by the friction evaluations and worn surface detections, the superior lubricity and durability of CPDs-c are mainly attributed to the synergy between the interfacial adsorption of polymeric shells, the nano-lubrication effects of carbon cores, and the establishment of CPDs-inserted tribofilm with a uniform thickness of about 86 nm. This work explores a green and facile strategy for synthesizing the CPDs toward oil lubrication and reveals the lubrication mechanism of CPDs, which facilitates the practical application of CPDs in tribology.

Tribological behaviors and mechanisms of surface-modified sepiolite powders as lubricating oil additives

Natural sepiolite powders were modified and refined using a mechanochemical wet modification process, and one-dimensional sepiolite powders were prepared and stably dispersed in the lubricating oil. An orthogonal experimental method of 4-factors and 3-levels is applied to investigate the effect of load, reciprocating frequency, sliding duration and content on tribological behaviors of sepiolite as additives in 500SN mineral base oil using a reciprocating sliding wear tester. The morphology, microstructure, chemical composition and state, and micromechanical properties of the worn surfaces were analyzed using scanning electron microscopy (SEM), focused ion beam (FIB) and transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and nanoindentation tester. The lubrication and friction-reduction mechanisms of the sepiolite additives are discussed in detail. The results indicate that the order of factors affecting the friction-reducing performance of sepiolite additives can be given as: sepiolite content, sliding duration, applied load and reciprocating frequency. On the other hand, the influence of the factors on the anti-wear property is: reciprocating frequency > sepiolite content > sliding duration > applied load. A tribolayer consisting of metal oxides, ceramic particles, graphite and organics is formed on the worn surface, which is conducive to the excellent tribological behavior of sepiolite due to its excellent lubricity, high hardness and low elastic modulus. The formation of the tribolayer is closely related to the unique physicochemical properties of the one-dimensional mineral clay and tribological conditions.

A novel multifunction fracturing fluid compounding of nano-emulsion and viscous slickwater for unconventional gas and oil

Visous slickwater formed by high viscous friction reducer (HVFR) has been a great success in replacing conventional slickwater in unconventional reservoir. In order to further extend the function of the slickwater to achieve the purpose of multi-effect of one recipe, a new fracturing fluid system composed of nano-emulsion and HVFR was introduced. It combines the functions of nano-emulsion and HVFR to form a new multi-functional fracturing fluid system: it can not only combine the advantages of conventional slickwater and guar gum fracturing fluid, but also avoid their disadvantages. At the same time, it has the effect of spontaneous imbibition oil displacement to enhance oil recovery, realizing the goal of combination of hydraulic fracturing and EOR. Whether the FR-900 drag reducing agent solution meets the fracturing fluid index is studied through the tests of rheological properties, drag reduction properties and sand carrying performance; CND is studied through the tests of wetting angle, demulsification rate, interfacial tension and spontaneous imbibition experiment. The synergistic effect of CND and FR-900 was analyzed by microscopic test at last. The result shown that: 1) CND can enhance the rheological properties and sand-carrying performance of FR-900 solution. After adding CND, the viscosity and viscoelasticity of FR-900 solution were improved, and the single particle sand-carrying performance and dynamic sand-carrying performance of FR-900 solution were also enhanced. The addition of CND has no effect on the friction reduction performance of FR-900. 2) the main component of CND is surfactant oil for imbibition oil displacement. The mixture of CND and FR-900 has the effect of wettability, reducing oil–water interfacial tension and fast demulsification. The experimental results of imbibition oil displacement show that 0.10 wt% CND can improve the oil recovery of FR-900 solution by 12.79%. The mixed solution of CND and FR-900 has the properties of easy breaking and low residue. 3) the field application results show that the new multifunctional fracturing fluid system has the advantages of low operation pressure, high sand-carrying performance and stimulation effects.

Explore the Tribological Effects of Two N-Containing Functional Groups on O/W Emulsion

Two water-soluble N-containing additives without sulfur and phosphorus, hexanamide with tetraethylenepentamine (EEHA) and benzotriazole amide with diethylenetriamine (BTAA), were synthesized and used as additives in the oil-in-water emulsion to investigate the effect of amino and benzotriazole ring on the tribological properties of the emulsion. The results showed that EEHA/BTAA exhibited wear resistance under all tested conditions. This may be attributed to the basic amino-functional groups in the additives which reduce the corrosive wear of the base emulsion. BTAA-emulsion showed the best friction-reducing and anti-wear performance under the 3 N loading condition, which may be attributed to its benzotriazole ring, which cannot be easily decomposed and could form self-assembled layers through π–π stacking. This π–π stacking may effectively compensate for the low chemical reactivity of the benzotriazole ring, and serve as a better protective film to exert tribological properties.

Molecular structure insight into the tribological behavior of sulfonate ionic liquids as lubricants for titanium alloys

The wide industrial application of titanium alloys requires lubricating materials with superior performance. Although ionic liquids have been recognized as potential choices for excellent lubricants, research on their tribological properties as applied to titanium alloys is not mature and systematic. In this work, a series of halogen-free sulfonate IL lubricants with different anions and cations were designed, synthesized, and applied to the titanium alloy (Ti-6Al-4V) friction pairs. From the perspective of molecular structure, the influencing factors on their physicochemical properties (thermal stability, viscosity) and tribological performances (friction-reducing and anti-wear performances) were explored, including the influences derived from their active element, chain length, molecular rigidity and branched chain structure. The lubricating mechanism contributed by the IL molecules and the Ti surfaces during sliding were analyzed by means of SEM, XPS, ECR and QCM. The results showed that physical adsorption and tribo-chemical reactions were involved during the sliding process. And the lubricating performances of the synthesized ILs may largely depend on their ability to form physical/chemical adsorption films on the titanium interfaces. The rigid benzene ring structure and flexible alkyl chain are conducive to strengthening the stability and efficiency of the formed interfacial tribo-film.

Different tribological behavior of CrN and CrCuN coatings under glycerol lubrication

The study compares and deciphers the differences in tribological performance of CrN coatings after incorporation of Cu moiety, i.e. CrCuN coatings, prepared using DC magnetron sputtered physical vapor deposition (PVD), under glycerol lubrication conditions. The structures, compositions and mechanical properties of the coatings were investigated by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), atomic force microscopy (AFM), and nano-indentation. CrCuN coatings present superior mechanical characteristics than CrN coatings. Reduced COF and wear rate values were observed more for the CrCuN coating than the CrN coating. The reason why glycerol exhibits better friction-reducing and wear protection performance in CrCuN coatings than CrN coatings is explained using X-ray photoelectron spectroscopy (XPS). Glycerol molecules were found to be easily degraded on the surface of the CrCuN coating during the sliding process to form a tribofilm which can greatly reduce the friction and wear.

Experimental study of Carbon Nanotubes to enhance Tribological Characteristics of Lubricating Engine Oil SAE10W40

Wear and friction had always been key factors in the functioning of advanced machines. Machine components containing high-performance oil cannot withstand increasing temperatures and intense pressures; therefore, additives improve different lubricants’ parameters and performances. Lubricating oil is the only element that can minimize wear and friction while simultaneously protecting materials from wear. The relative movement between two surfaces is impossible without a lubricant. As a result, for a more complex machine, stern lubrication is necessary. Nanomaterials play a vital role and have tendency to improve tribological properties. Carbon nanotubes (CNTs) are most popular due to numerous applications in different fields on account of their excellent chemical, electrical, thermal, mechanical, and optical properties. This study aims to research the tribological activity of carbon nanotubes (CNTs) with a four-ball tribotester. Furthermore, SWCNTs and MWCNTs as an additives in SAE10W40 motor oil were also tested to evaluate its tribological characteristics. In compared to industrial engine oil without SWCNT and MWCNT, using MWCNTs as additives in the engine oil reduced the worn scar diameter by 67 percent, while utilising SWCNTs as an addition reduced the worn scar diameter by 38 percent. The average friction coefficient with MWCNTs is decreased by 56%, and with SWCNTs is decreased by 48%; this may be due to the effect of viscosity. The provided experimental result conveys that the lubricating oil with multiwall carbon nanotubes exhibit higher performance in anti-wear and decrease friction reduction compared with single-walled carbon nanotubes.

Nitrogen-doped porous carbon nanospheres derived from hyper-crosslinked polystyrene as lubricant additives for friction and wear reduction

A novel porous carbon nanospheres doped with nitrogen (N@MCNs) was prepared from hyper-crosslinked polystyrene nanospheres with melamine-assisted carbonization. The N element are found to be evenly distributed in the entire carbon nanospheres, the as-prepared N@MCNs are effective in reducing friction and wear as an additive, which was attributed to the robust protective films that occurred because of tribo-chemical reactions induced via N@MCNs. The formation of protective films comprising nitrides and metal oxides can improve anti-wear and friction reduction performance of 500SN. The friction coefficient of N@MCNs was reduced from 0.413 to 0.11, the wear volume was reduced by 83.5%. The experiment provides a reliable and effective approach to preparing co-doped carbon nanospheres from inexpensive polystyrene for friction and wear reduction.

Study on the Liquid-Liquid and Liquid-Solid Interfacial Behavior of Functionalized Graphene Oxide.

With the rise of carbon neutrality, the applications of carbon-based materials are gaining considerable attention. Graphene oxide (GO) is a two-dimensional sheet with epoxy and hydroxyl groups on the basal plane and carboxyl groups at the edge. In order to change the oil/water (o/w) interfacial activity, GO was controlled and modified by dodecylamine to get two kinds of functionalized GOs (fGOs), named as basal plane-functionalized GO (bGO) and edge-functionalized GO (eGO), respectively. The interfacial tension measurement showed that fGOs could reduce more interfacial tension at the poly-α-olefin/water interface than those at synthetic esters or aromatic compounds/water interfaces. Besides, eGO can reduce more poly-α-olefin-4/water interfacial tension compared to bGO. The interfacial dilatational rheology of eGO and fatty alcohol polyoxyethylene ether-4 (MOA4) showed that MOA4 gradually replaced eGO at the interface with the increase of MOA4, until the interface was completely occupied. eGO and MOA4 complex emulsion exhibited the best friction-reducing performance at 250 rpm. The coefficient of friction (COF) curves of the emulsions with eGO showed two platforms, with the COF reduced by 37.42% at the most. The rheological results of emulsions showed that the addition of eGO increased the elasticity of the emulsion. Emulsions showed shear-thinning and friction-thickening properties, which make it easier for the emulsion to form a lubricating film on the metal surface. Our research results suggested that the functionalization on the edge of GO will change the interfacial properties significantly, which have widespread applications in the encapsulation of active materials, surface protection, adsorption, and separation of pollutants.

Effect of Mainstream Oxygen Concentration on Supersonic Film Cooling and Friction Reduction Performance Using Hydrocarbon Fuel

Effect of Mainstream Oxygen Concentration on Supersonic Film Cooling and Friction Reduction Performance Using Hydrocarbon Fuel

Effective corrosion and wear protection of slippery liquid-infused porous surface on AZ31 Mg alloy

Magnesium alloys possess many exceptional advantages and attract much interest from researchers. However, the poor corrosion resistance significantly restricts their extensive applications in industry. Herein, a slippery liquid-infused porous surface (SLIPS), with good surface hydrophobicity, anti-corrosion, anti-wear, self-cleaning and self-healing performances, was developed on AZ31 Mg alloy. MgAl-layered double hydroxides (LDHs) with nanoporous structure were first in-situ synthesized on AZ31. Especially, an environmentally friendly corrosion inhibitor of sodium benzoate was intercalated into MgAl-LDHs to improve the corrosion resistance. After low-surface-energy modification and infusion of lubricant, the desired SLIPS with a homogeneous liquid layer was finally formed. The SLIPS showed good repellency to water to provide superior corrosion protection for the underlying AZ31, with the lowest corrosion current density of 1.93 × 10−9 A cm−2 and the largest impedance modulus of 1.18 × 107 Ω cm2. In comparison with the bare AZ31, the SLIPS exhibited enhanced friction-reducing and anti-wear performance because of the lubricating effect of the infused silicone oil and nanosheets of MgAl-LDHs. In addition, the SLIPS performed well in the self-cleaning and self-healing tests, showing potential to be widely used to enlarge the industrial applications of Mg alloys.

Research Progress of Nano Copper Lubricant Additives on Engineering Tribology

Nanoparticles have as characteristics super sliding, extreme pressure, self-healing, etc., which can improve the friction reduction and anti-wear performance of sliding components, when used as lubricating oil additives. Nano-copper particles have a good synergistic effect with other antifriction agents, anti-wear agents, antioxidants and grease additives because of their low shear strength and grain boundary slip effect, showing a better anti-friction and anti-wear effect. However, nanoparticles are prone to conglomerate, and this causes a bottleneck in the application of dispersant for nano-copper in a lubricating oil system. The regulation of nanosized effect and surface properties has great engineering significance in compensating for the precision in manufacturing accuracy. This paper comprehensively reviews the tribological research progress of nano-copper as a lubricant additive, which provides a reference to the application of nano-copper particles as lubricating oil additives on engineering tribology.

Suppressed MoO3/FeMoO4 formation in molybdenum dialkyl-dithiocarbamate-derived tribofilms on nitrogen-incorporated Al-Mg-Ti-B coatings

The tribo-chemical interplays between hard coatings and lubricant additives have attracted considerable attentions during recent years. It has been demonstrated that Al-Mg-Ti-B coatings exhibit a good tribo-chemical compatibility with typical lubricant additives zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyl-dithiocarbamate (MoDTC). Herein, a systematic study was conducted on the tribological behaviors of N-incorporated Al-Mg-Ti-B coatings under MoDTC lubrication. By addition of N in the coatings, TiO2 at the coating surfaces was found to be partially reduced into TiO2−x. Notably, the formation of MoO3 and/or FeMoO4 was shown to be substantially suppressed in MoDTC tribofilms on N-incorporated Al-Mg-Ti-B coatings, resulting in a MoS2-dominated MoDTC tribofilm formed on the coating surfaces. Such interesting tribo-chemical behavior has been tentatively explained in terms of excess charge transfer from TiO2−x and subsequent reduction of MoDTC decomposition intermediates MoSxOy and/or MoSz, thereby preventing the MoO3 and/or FeMoO4 formation in MoDTC tribofilms. This finding may provide a new approach for improving the friction reduction performance of MoDTC-lubricated tribo-contacts.

Effect of carbon nanotubes additive on tribocorrosion performance of micro-arc oxidized coatings on Ti6Al4V alloy

Ti6Al4V alloy subjected to the combined effects of wear and corrosion (tribocorrosion) in corrosive media shows severe deterioration. This study aimed to investigate the tribocorrosion behavior of oxide films produced by micro-arc oxidation (MAO) in a 3.5% NaCl solution. MAO ceramic coatings were obtained on Ti6Al4V alloy using the MAO process in alkaline electrolytes with different carbon nanotubes (CNTs) concentrations. The morphology and composition of MAO coatings were investigated using SEM, XRD, and Raman spectroscopy. Their friction reduction and wear resistance performance was evaluated under dry sliding conditions. Potentiodynamic polarization was used to assess the corrosion resistance of the MAO-coated Ti6Al4V specimens. Tribocorrosion behavior was evaluated by the evolution of open circuit potential (OCP) and coefficient of friction (COF) before, during, and after reciprocating sliding. The results showed that CNTs were incorporated in MAO coatings obtained in electrolytes containing CNTs and enhanced MAO coatings' corrosion and tribocorrosion resistance. The MAO coatings obtained in electrolytes containing 0.15 g/L CNTs possessed the best corrosion and tribocorrosion resistance.

Optimization and friction reduction study of a new type of viscoelastic slickwater system

Slickwater is widely used in unconventional reconstruction, but its sand-carrying capacity is weak, and the influencing factors of friction reduction are not clear. To cope with various complex working conditions, it is necessary to develop a new system with strong sand-carrying capacity and good friction reduction tolerance. In this paper, polymer with high friction reduction rate is selected firstly, and then a new type of viscoelastic slickwater system is formed by adding nano-emulsion. Then, the relationship between the friction reduction performance and temperature, shear flow, salinity of the slickwater system was studied. The influence on the microstructure of the slickwater with the change of friction reduction rate under various factors was analyzed by using electron microscope. The viscoelasticity and viscosity of the slickwater system were evaluated by using rheometer. Finally, based on the D&M formula, the friction calculation model suitable for viscoelastic slickwater system is established and verified with field application. The results showed that the friction reduction performance was improved slightly after the combination of the high friction reduction slickwater and nano-emulsion, and the resistance to salt, shear, and temperature was better; The intersection point of viscoelastic modulus curve moved from 0.47 Hz to 0.10 Hz, and the network structure of the tissue was more well developed, and the law of friction reduction can be could be fitted by the D&M formula; It is found that it has good consistency by fitting the field data through the friction reduction model. It provides theoretical support for the improvement of efficiency, mechanism research, and on-site friction prediction of slickwater system products in the future.

Research Progress of Ionic Liquids as Lubricants.

Emerging ionic liquid lubricants were discovered only 20 years ago. The superior performance of ionic liquids over traditional lubricating fluids have been reviewed, including low-temperature fluidity, viscosity–temperature properties, thermal oxidation stability, ultralow volatility, incompressibility, electrical conductivity, friction coefficient under elastohydrodynamic lubrication conditions, friction reduction and antiwear performance under boundary lubrication conditions, environmental friendliness, etc. The applications where ionic liquids are superior to traditional lubricant fluids are presented, including hydrogen compressor lubricating fluids and liquid pistons, oxygen compressor lubricating fluids, hydraulic fluids, space lubricants, vehicle engine oils, industrial gear oils, metalworking fluids, industrial coolant, micro/nano electromechanical system applications, electrical conductive lubricants, etc. The ability of ionic liquids to replace ZDDP, a key additive of lubricating oil, is introduced. The future development prospects of ionic liquid lubricants are analyzed.

Effects of the inclination angles of DLC end face micro-texture on the tribological properties of dry gas seal rings

To improve the tribological performance of the seal rings in the dry gas seal, the elliptical micro-textures with different inclination angles (0°, 45°, 90°, 135°) were processed on the end face of SiC static rings by nanosecond laser. Diamond-like carbon (DLC) films were then deposited on the micro-textured end face. Under dry friction condition, the end-face friction and wear test was conducted to simulate the actual working state of the dry gas seal at start-up phase. The effects of micro-texture inclination angles and DLC phase change on the tribological properties of seal rings were investigated. The possible friction reduction mechanism was analyzed. The results show that compared with the smooth surface, the elliptical micro-texture can effectively improve the tribological properties of DLC films. At the same time, the inclination angle of the elliptical micro-texture has a remarkable influence on the tribological properties. When the micro-texture inclination angle is 90°, the static ring sample has the best friction reduction and wear resistance performance. Compared with the untextured sample, the average friction coefficient is reduced by 46.15%. The wear reduction characteristics of the textured end face are mainly contributed to the capturing effect of the texture on wear particles.

What’s the Best Friction Reducer? You Need To Figure It Out Yourself

Friction reducers are expected to play critical roles in fracturing, some better than others. Shale producers are belatedly realizing that there are many variables that can alter the performance of these chemicals used to reduce the power needed to hydraulically fracture a reservoir, and in higher doses, to thicken fluid, making it possible to deliver proppant more efficiently. There are wells that can justify paying more for a friction reducer formulated to stand up to difficult chemical challenges, and others that cannot. But there is no guide that describes how these key additives perform. Those who do evaluations will realize that a lot of details about friction reducers are proprietary and no industry standard provides guidance about the information needed to thoroughly assess their compatibility with reservoir conditions. “There hasn’t been a really good method to quantitatively evaluate friction reducers and what they do,” said Paul Carman, the completion fluid advisor for ConocoPhillips, who has not figured out what that method might be. Recently, Occidental Petroleum took a stab at answering the question with a paper discussing its evaluation of friction-reducer performance. It’s not a short answer. The paper delivered at the Unconventional Resources Technology Conference (URTeC) does not offer names of the products tested, how many were tested at any stage of the process, or details that might identify top performers (URTeC 5249). Those who dig deeper and ask fracturing experts will learn that the best friction reducer will depend on the job. And money, time, and research are required to gather the data needed for informed decision making. When Occidental began working on a system to evaluate friction reducers, they found little had been written on how to do it, said Nancy Zakhour, Occidental’s well design lead, a coauthor of the paper. There was a general paper from Shell on well chemical evaluation but little else. That shows how oil companies have come to rely on others to do performance testing. The shale business has not shown much interest in chemical performance until recently. Greater attention has turned to the many details that can incrementally improve shale well performance and to the research showing how friction reducers perform badly due to chemical reactions in some wells. These are not the only additives that may be affected by chemical reactions during and after fracturing. But friction reducers have grabbed the most attention because they do a couple important jobs.