Polymer Stability in Multiviscosity Engine Oils

Lubricating oil composition for diesel engines with improved fuel consumption and shear stability. The composition contains two comb polymers with different molecular weights. One comb polymer has a lower weight average molecular weight (Mw < 300,000) and the other has a higher Mw (Mw > 400,000). The ratio of these comb polymers in the oil is 0.25 or more. This balance of lower and higher weight comb polymers provides better fuel consumption and shear stability compared to using just one comb polymer. The oil also contains a base oil, other additives like detergents and dispersants, and may further contain pour point depressants, rust inhibitors, extreme pressure additives, and defoamers.

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Enhanced oil recovery (EOR) methods are generally employed in depleted reservoirs to increase the recovery factor beyond that of water flooding. Polymer flooding is one of the major EOR methods. EOR polymer solutions (especially the synthetic ones characterized by flexible chains) that flow through porous media are not only subjected to shearing forces but also extensional deformation, and therefore, they exhibit not only Newtonian and shear thinning behavior but also shear thickening behavior at a certain porous media shear rate/velocity. Shear rheometry has been widely used to characterize the rheological properties of EOR polymer systems. This paper aims to investigate the effect of the polymers concentrations, ranging from 25 ppm to 2500 ppm, on the viscous, linear, and non-linear viscoelastic properties of hydrolyzed polyacrylamide (HPAM) in shear field and porous media. The results observed indicate that viscous properties such as Newtonian viscosity increase monotonically with the increase in concentration in both fields. However, linear viscoelastic properties, such as shear... Read More

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Polymer dynamics are special, in that they are always insensitive to the chemical details of the monomers. However, recent experiments show that the nonlinear extensional rheology of concentrated polymeric liquids has a nonuniversal feature. In this work, the variation of segmental frictional coefficient under flows, which is thought to be the critical factor in explaining the observed nonuniversality, is investigated in the coarse-grained (CG) molecular dynamics (MD) simulations of polymer melts. The frictional coefficients in the simulations are quantified from the expressions we proposed very recently [Jiang, N.; van Ruymbeke, E., Macromolecules 2023, 56 (8), 29112929], which are based on the analytical relationships between the frictional coefficients and the observable rheological and structural properties. After the validation of the simulations with experimental data and our expressions, it is shown that those frictional coefficients can be universally related to the projection areas of the polymer coils in the plane normal to the direction of elongation. Moreover, this proje... Read More

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Lubricating oil composition with high viscosity index, comprising a base oil with a kinematic viscosity of 2.0-7.0 mm2/s at 100°C and a polymer with a specific molecular structure, wherein the polymer has a ratio of peak integral values at 10.0-11.0 ppm to 13.5-14.5 ppm of 0.05 or more as determined by 13C-NMR analysis.

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Abstract This work presents a viscosity model based on the Giesekus equation. The model is shown to be more flexible than the Cross and Carreau models in representing the shear-thinning behavior of viscoelastic fluids. It has been investigated that the influence of the model parameters on the viscosity showed that the mobility parameter plays a distinctive role in adjusting the inflection shape of the viscosity curve. The results show that the new model is able to accurately capture the shear-thinning behavior of polystyrene data, while the Cross and Carreau models tend to underestimate and overestimate the viscosity at the inflection point, respectively. It has been also shown that the Yasuda-type modification is also applicable to the proposed model. Moreover, the viscosity model has been applied to simultaneously fitting a polymeric liquid system and a particulate slurry system. The new viscosity model is a promising tool for modeling the shear-thinning behavior of viscoelastic fluids in a wide range of applications.

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The research presented proposes a new methodology for measuring degradation of polyamide 11 (PA11), as an alternative to the classic criterion established by the American Petroleum Institute in API17TR2. PA11 flexible pipes may be subjected to different degradation conditions, being hydrolysis one of the main aging mechanisms. Aged PA11 pressure barriers coming from flexible pipelines were sliced into inner and outer parts, having a pristine PA11 as a reference. Rheological measurements were performed on air and inert (N2) atmospheres. Mark-Houwink Equation was used to correlate zero-shear viscosity with molecular weight (Mw) and corrected inherent viscosity (CIV). PA11 showed a shear thinning behavior, with higher zero-shear values with the increase in CIV. Cross and power law models were adopted for apparent viscosity behavior prediction purposes with over R2> 90 %. The shifting of the crossover points of elastic (G) and loss modulus (G) showed a correlation with molecular weight and molecular weight distribution (MWD). Based on ColeCole, real () and imaginary () components ... Read More

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Abstract The rheological properties of lubricating greases are determined by the viscosity of the base oil, the interaction between base oil and thickener, and the interaction between thickener particles. The contribution of the oilthickener interactions to the viscosity is well known, but the contribution of the thickenerthickener interactions has not yet been studied by employing theoretical or computational frameworks. In this paper, we use coarse-grained molecular dynamics to simulate a fibrous microstructure, and we show that the experimentally observed viscoelastic/plastic behaviour can be well reproduced. A parametric study shows that the apparent viscosity increases with increasing fibre length, fibre stiffness and thickener concentration. This is as expected, showing that this modelling approach is useful to study effects on grease rheology that are not accessible experimentally, such as impact of fibre entanglement or agglomeration.

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The aging of lubricants is a primary factor contributing to rolling bearing failures. The rolling stability test simulated the aging behavior of grease under shear and high-temperature circumstances. An investigation was conducted on how mechanical-thermal aging impacts the chemical and physical structures of polyurea grease, as well as how changes in thickener microstructure affect rheological and tribological properties. The results show that under shear and high temperature, structural changes in urea lead to a transformation of the thickener morphologies from the growth of entangled ribbon fiber to a large-diameter rod structure, with a significant decrease in the degree of entanglement. When a certain proportion of fibrous and rod structures coexist, the grease has good oil separation capacity, the structural stabilities of grease become weak, and the deformation resistance decreases. During this phase, the polyurea grease has the best tribological performance.

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This study employed Molecular Dynamics (MD) simulations to examine the tribological impact of polyalkylmethacrylate (PAMA), a polar lubricant additive known for its role as a Viscosity Index (VI) improver, when combined with the non-polar lubricant polyalphaolefin (PAO) 6. Examining the solid-lubricant interface in a confined liquid between iron surfaces with a Couette flow, the research delves into molecular interactions, emphasizing mechanisms governing wall slip for both non-polar and polar molecules.Notably, for non-polar molecules, a singularity in slip length is observed with a molecular-scale gap height resulting in an infinite slip length.However, the addition of polar additives eliminates slip, leading to increased friction.Furthermore, in terms of bulk shear, the introduction of polar additives reduces shear thinning as temperature increases.This dual observation highlights the substantial impact of polar additives on both wall slip behavior and bulk shear properties in the lubricant system.

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Under the parameters of normal engine operation, lubricating oil typically experience periodic shifts in its viscosity. Because of this, engine oils often include polymeric additives that are referred to as viscosity modifiers. The oil is able to give acceptable fluid lubrication at extreme temps due to these additives, which are oil-soluble polymers. The aim of present work to use polymers in form of nano-composites such as Styrene, Octadecyl-methacrylate (ODMC) and Dodecyle-methcrylate (DDMC) for lube oil viscosity index and pour point enhancement during copolymerization reaction. The benzoyl peroxide was used as an initiator. Solubilizes were made using SN-150 mineral base oil from the Al-Dorha refineries in Baghdad, which had a viscosity index of 128, and a viscosity range of 0 to 100C. Styrene and methacrylate monomer combinations were copolymerized in an SN-150 mineral base oil solution in a nitrogen atmosphere at 60-80C. A 200 mm3 oil glass reactor fitted with a magnetic stirrer and a reflux condenser was used to conduct the reactions. Five percent by weight of the total mon... Read More

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Addition of particles to a viscoelastic suspension dramatically alters the properties of the mixture, particularly when it is sheared or otherwise processed. Shear-induced stretching of the polymers results in elastic stress that causes a substantial increase in measured viscosity with increasing shear, and an attractive interaction between particles, leading to their chaining. At even higher shear rates, the flow becomes unstable, even in the absence of particles. This instability makes it very difficult to determine the properties of a particle suspension. Here, we use a fully immersed parallel plate geometry to measure the high-shear-rate behavior of a suspension of particles in a viscoelastic fluid. We find an unexpected separation of the particles within the suspension resulting in the formation of a layer of particles in the center of the cell. Remarkably, monodisperse particles form a crystalline layer which dramatically alters the shear instability. By combining measurements of the velocity field and torque fluctuations, we show that this solid layer disrupts the flow instabi... Read More

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Abstract Shear viscosity and elasticity have been identified as two of the most influential factors controlling the volume of drilling fluid invasion into reservoir and the resultant formation damage. Past studies were inconclusive regarding individual effects of fluid shear viscosity vs elasticity, as it was challenging to disintegrate and measure their impacts independently. Therefore, we investigated the relative contributions of the fluid shear viscosity and the elasticity on the fluid invasion and the resultant productivity impairment. 24 water-based drilling fluids were prepared using various blends of three different molecular weight PHPA polymers. Detailed rheological characterizations of these fluids were carried out by conducting amplitude sweep and controlled shear rate tests. Viscoelastic properties of the fluids were quantified in terms of energy dissipation, which physically signifies the amount of energy required per unit volume to cause an irreversible deformation in the fluids internal structure. Static filtration tests and core flooding experiments were conducted t... Read More

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In this paper, the two-dimensional KelvinHelmholtz (KH) instability occurring in the shear flow of polymer fluids is modeled by the dissipative particle dynamics (DPD) method at the coarse-grained molecular level. A revised FENE model is proposed to properly describe the polymer chains. In this revised model, the elastic repulsion and tension are both considered between the adjacent beads, the bond length of which is set as one segments equilibrium length. The entanglements between polymer chains are described with a bead repulsive potential. The characteristics of such a KH instability in polymer fluid shear flow can be successfully captured in the simulations by the use of the modified FENE model. The numerical results show that the waves and vortexes grow more slowly in the shear flow of the polymer fluids than in the Newtonian fluid case, these vortexes become flat, and the polymer impedes the mixing of fluids and inhibits the generation of turbulence. The effects of the polymer concentration, chain length, and extensibility are also investigated regarding the evolution of KH i... Read More

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The rheology problems of non-Newtonian oil, accompanied by the physical phenomena of formation and destruction of coagulation structures and aggregates, significantly affecting the flow are considered and analyzed. Also are considered issues of hydrodynamic interaction of particles leading to the formation of disordered structures, which significantly change the rheological properties of non-Newtonian oil. It has been noted that the formation of coagulation structures depends on energy dissipation, viscosity, stress or shear rate, and the size of the particles forming the structure. With increasing asphalt-resin content in the oil, the probability of particle collision increases, increasing the rate of formation of various disordered structures up to a framework that nullifies the rate of oil flow. Applied problems of rheology, including dissolution kinetics of asphalt-resinous substances in aromatic hydrocarbons and improving rheological properties of the oil, rheology of structured non-Newtonian oils in gas lift method of production, as well as possible ways to create new technolog... Read More

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In order to help one to judge the friction properties of lubricating oils without tests, this paper intends to establish the correlation between the characteristic parameters of lubricating oils and the friction properties. The elastohydrodynamic and boundary friction properties of poly alpha olefin (PAO) synthetic oil, polyol ester oil and paraffin-based mineral oil were tested using a Mini-Traction Machine. Fourier transform infrared microscopy is used to identify material changes before and after friction tests. The kinematic and dynamic viscosities of the three lubricating oils were measured using a petroleum product viscosity tester and a rotating rheometer. The results show that the kinematic viscosity does not directly determine the COF (coefficient of friction) of the lubricating oil, but the higher the dynamic viscosity, the higher the COF of the lubricating oil. The higher the viscosity-pressure coefficient, the lower the viscosity index (the worse the viscosity-temperature performance), and the higher the COF of the lubricating oil, which is related to the adaptability of ... Read More

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Viscous and elastic behaviors of the crude oil-polymer emulsions were studied experimentally through Creep-recovery investigation. Two different types of polymers of Alcoflood and Xanthan were investigated in this study to represent the synthetic and bio-polymers. A Rheostress RS100 in controlled stress CS-mode was utilized to carry out all the experimental results and assessments. The viscous and elastic investigations of the crude oil-polymer emulsions were examined for polymer concentrations of 0104 ppm, 075% by volume of crude oil, and two candidates of each polymer. This experimental study resulted that the polymer and crude oil concentrations exhibited significant impact on the compliance behavior. For polymer concentrations higher than 103 ppm, the crude oil-Xanthan emulsions exhibited higher recovery% than the oil-Alcoflood emulsions. The ability of the Xanthan gum to form elastic characteristic within the crude oil emulsion is higher than the Alcoflood polymer material.

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The shear rheology of particle suspensions in shear-thinning polymeric fluids is studied experimentally using parallel plate measurements and numerically using fully resolved, 3D finite volume simulations with the Giesekus fluid model. We show in our experiments that the steady shear viscosity and first normal stress difference coefficient of the suspension evolve from shear-thickening to substantially shear-thinning as the degree of shear-thinning of the suspending fluid increases. Moreover, in highly shear-thinning fluids, the suspension exhibits greater shear-thinning of the viscosity than the suspending fluid itself. Our dilute body-fitted simulations show that in the absence of hydrodynamic interactions, shear-thinning can arise from the particle-induced fluid stress (PIFS), which ceases to grow with increasing shear rate at low values of (solvent viscosity ratio) and finite values of (the Giesekus drag coefficient). In a Giesekus suspending fluid, the polymers surrounding the suspended particle are unable to stretch sufficiently at high Weissenberg numbers (Wi) and the redu... Read More

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This review is devoted to understanding the role of elasticity in the main flow modes of polymeric viscoelastic liquidsshearing and extension. The flow through short capillaries is the central topic for discussing the input of elasticity to the effects, which are especially interesting for shear. An analysis of the experimental data made it possible to show that the energy losses in such flows are determined by the Deborah and Weissenberg numbers. These criteria are responsible for abnormally high entrance effects, as well as for mechanical losses in short capillaries. In addition, the Weissenberg number determines the threshold of the flow instability due to the liquid-to-solid transition. In extension, this criterion shows whether deformation takes place as flow or as elastic strain. However, the stability of a free jet in extension depends not only on the viscoelastic properties of a polymeric substance but also on the driving forces: gravity, surface tension, etc. An analysis of the influence of different force combinations on the shape of the stretched jet is presented. The con... Read More

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Polymer flooding is one of the techniques used to enhance oil recovery from depleted hydrocarbon reservoirs. Although this technology is popular for this application, the shearing effect in the injection process causes poor performance, which is an obstacle to meeting the needs of the formation. An experimental evaluation of the rheological properties, viscoelasticity, hydrodynamic size, static adsorption, and seepage characteristics of the associated polymer solution before and after shearing was conducted to determine the influence of shearing on the polymer solution. The results show that the effect of shear on the polymer was irreversible, and the properties of the polymer solution damaged by shear were attenuated. After the critical associating concentration, the associated polymer can recover its solution properties through hydrophobic association, which can improve the shear resistance of the polymer solution and make its own rheological law and reduce the viscoelastic change. Although the hydrodynamic size, viscoelasticity, and adsorption capacity of the polymer solution afte... Read More

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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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