Reduce Friction Losses Research Articles

Experimental and numerical studies of thermal power conversion and energy flow under high-compression ratios of a liquid methane engine (LME)

To improve the performance of a liquid methane engine (LME) under universal characteristics, the in-cylinder combustion process and thermal power conversion under different compression ratios were studied by experiment. The experimental results show that increasing the compression ratio results in a linear increase in EEE (effective expansion efficiency) and EER (effective expansion ratio). Moreover, the thermal efficiency varies significantly with the compression ratio only at low and medium loads. The effective thermal efficiency can reach up to 48.69%. For high-speed conditions, it is recommended to reduce friction losses and pump gas losses. Furthermore, a 1-D simulation model was developed to simulate the in-cylinder energy flow with a compression ratio of 12.6. The simulation results show that exhaust timing has a more pronounced effect on the in-cylinder energy flow (thermal balance) than intake timing. When the engine speed is 800 rpm, advancing the exhaust timing by 20°CA can increase the effective thermal efficiency by about 1%.

Theoretical and Numerical Investigation of Reduction of Viscous Friction in Circular and Non-Circular Journal Bearings Using Active Lubrication

Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by adjusting the rotor position. This work provides a theoretical justification for the mechanism of this effect for the cases of purely laminar lubricant flows in journal bearings. The operating modes connected with the transition to turbulent phenomena and the occurrence of Taylor vortices are beyond the scope of this paper. Conditions that ensure the minimization of friction losses in hydrodynamic and hybrid bearings with hydrostatic parts are determined based on the equations describing viscous friction in a fluid film. In non-adjustable plain hydrodynamic bearings, the minimum of friction is achieved with the centered shaft position that is actually unstable due to the resulting forces configuration. In actively lubricated hybrid bearings, a further reduction in viscous friction is possible by combining film thickness and pressure distributions. Recombining them, along with adjustment of the shaft position, allows the optimization of the distribution of shear stresses in the fluid film. As a result, the shear stresses caused by the rotation of the shaft can be partially compensated by the stresses caused by the pressure gradient, reducing the torque-resisting rotation. In addition, additional benefits can be obtained in the minimum friction state by the reduced lubricant flow and power losses to its pumping. A series of numerical calculations for elliptical, 3-, and 4-lobe bearings show that non-circular bores provide additional variability in film thickness distribution and a premise for optimizing the bearing tribological parameters. Four-lobe bearing demonstrated the best ability for reducing viscous friction among the considered designs. The results obtained can be used as a basis for further optimization of the geometry of fluid film bearings of both active and passive designs by reducing power losses due to viscous friction.

Multi-objective optimization on internal cooling strategies for gas turbine blade leading edges

In this work, multi-objective optimization on internal cooling strategies is performed for gas turbine blade leading edges, aiming to maximize the heat transfer rate and minimize the friction loss. Inspired by previous advanced internal cooling concepts (swirling cooling, impingement cooling and double impingement cooling), four geometrical parameters are determined as design variables, including the deformation length of impingement chamber, the horizontal position and incline/compound angles of nozzles. A series of validated numerical simulations based on Reynolds Averaged Navier-Stokes equations are performed to provide sufficient training source and generate accurate surrogate model. Two cooling strategies are optimized by genetic algorithm, and their heat transfer and flow characteristics are compared with the previous cooling methods. By the optimized structures, the area with high Nusselt number enlarges, and the heat transfer rate distributes more uniformly. Compared to swirl cooling, the optimized strategies can obtain a heat transfer enhancement of 7.5% to 15.5% with a friction loss reduction of 6.7% to 0.5%, when Reynolds number is 18500. Correspondingly, the comprehensive aerothermal efficiency is improved by at least 15.8%. Moreover, the effects of the four design variables are discussed, and the design guidance of internal cooling for blade leading edges is provided thereby.

Thermal evaluation of flow channels with perforated-baffles

The influences of perforated-baffles on the local Nusselt number (Nu) and thermo-hydraulic behaviors were comprehensively studied using thermochromic liquid crystal sheet. The perforated-baffles were designed in two forms: perforated-baffle (PB) and perforated-baffle with square wings (SW-PBs). Transverse solid baffles (TBs) were also tested for an assessment. All baffles had an identical height of 12 mm (e/H = 0.3). Experimental results showed that SW-PBs offered better Nu than PBs. It is also seen that PBs and SW-PBs caused lower pressure loss than TBs by around 20.49% and 13.98%, respectively. The reduction of friction loss was primarily due to the baffle perforation. In addition, the PBs yielded the thermal performance factors (TPF) up to 1.01 at the lowest Reynolds number of 6000.

Friction Reduction by Dimple Type Textured Cylinder Liners-An Experimental Investigation.

Applying texture to a surface in a tribological interface will influence frictional performance, which has been investigated in several previous studies. However, since varying operating conditions heavily affect the frictional performance and optimum texture dimensions, more work in this field is required. There are few experimental studies concerning the influence of texture on friction especially under sliding lubricated conditions and even fewer at high sliding speeds. In this work, the effect of texture on frictional losses between the piston ring and cylinder liner is studied experimentally. The texture is of the dimple type, with a diameter and depth of 300 µm and 3 µm, respectively, applied to the cylinder liner surface. Experiments are performed with sliding speeds close to real piston sliding speeds. A clear reduction in frictional losses is observed with the textured cylinder liner. Moreover, qualitatively comparing the experimental results to a numerical model shows a good correlation.

Experimental Research on the Surface Quality of Milling Contour Bevel Gears

Contour bevel gears have the advantages of high coincidence, low noise and large bearing capacity, which are widely used in automobile manufacturing, shipbuilding and construction machinery. However, when the surface quality is poor, the effective contact area between the gear mating surfaces decreases, affecting the stability of the fit and thus the transmission accuracy, so it is of great significance to optimize the surface quality of the contour bevel gear. This paper firstly analyzes the formation process of machined surface roughness of contour bevel gears on the basis of generating machining method, and dry milling experiments of contour bevel gears are conducted to analyze the effects of cutting speed and feed rate on the machined surface roughness and surface topography of the workpiece. Then, the surface defects on the machined surface of the workpiece are studied by SEM, and the causes of the surface defects are analyzed by EDS. After that, XRD is used to compare the microscopic grains of the machined surface and the substrate material for diffraction peak analysis, and the effect of cutting parameters on the microhardness of the workpiece machined surface is investigated by work hardening experiment. The research results are of great significance for improving the machining accuracy of contour bevel gears, reducing friction losses and improving transmission efficiency.

Choosing of rational periodicity of engine crankcase oil changing taking into account energy-saving properties of oils

It is known that reducing friction losses and, consequently, wear is the most important function of engine crankcase oil. Many oil manufacturers add additives to the oil composition - thickening and friction modifiers. Achieving a rational periodicity of crankcase oil changing generally reduces the operating consumption of oil, the cost of which accounts for a significant share of the total cost structure of operating costs. The developed method for evaluating the energy-saving properties of the researched three grades of oil by viscosity-temperature characteristics allows for reducing the cost of conducting special research. The viscosity value's dependence on the temperature range from 20 to 100 ° is experimentally established. This work presents part of the research results to justify the choice of rational changing periodicity of diesel engines’ crankcase oil, considering the energy-saving properties of oils. During operation, it is also necessary to comply with the requirements for preserving the recommended grades of fuel and lubricants, observing their use and safety modes, and a reasonable oil level in the crankcase.

Hybrid CFD-ANN approach for evaluation of bio-inspired dolphins dorsal fin turbulators of heat exchanger in turbulent flow

The central aim of the present investigation is to evaluate the effects of bio-inspired Dolphin’s dorsal fin turbulators (DFTs) with a hybrid CFD-ANN approach in a counter flow double pipe heat exchanger. The DFT’s physical model is adapted from the infrared thermal image of a bottlenose dolphin dorsal fin. The effects of different influential parameters, such as the length scale (D) of DFTs including 4, 8, 12 mm and the number of turbulators (N) including 6, 10, and 14 are numerically examined at different Reynolds numbers. Also, using CFD data, the neural network is trained with great accuracy of R2 above 0.999. Important parameters such as Nu, f, Ɛ, NTU can be predicted in different conditions by the ANN method. This method greatly reduces the costs of CFD solutions, which is advantageous. The results indicate that the DFT's streamlined geometry could significantly reduce friction loss by streamlining the fluid flow. Also, colliding the fluid stream with the DFTs improves heat transfer by boundary layer destruction. The UA Ratio (UAR) of the Dolphin’s dorsal fin turbulator heat exchanger (DFTHE) to the simple heat exchanger (SHE) is between 1.02 and 1.74. Also, the ratio of Nu, Ɛ, NTU for the DFTHE to the SHE is equal to 2.48, 1.63, and 1.74, respectively.

Numerical analysis of flow characteristics of the oil-water mixture in stratified-annular horizontal pipe

The loss of oil fluid flow in the piping system in the petroleum industry due to friction is the cause of low efficiency. To reduce friction loss, the viscosity of petroleum can be lowered by adding water as a mixture. Actually, the flow loss in a piping system is influenced by several factors including flow pattern, fluid type, flow velocity, flow pressure and pipe diameter. This study aims to determine the effect of flow patterns on changes in velocity in the two-phase flow of oil and water in a piping system. This numerical analysis research was carried out using Fluent 6.2 software with variations in the velocity of the oil-water mixture: 0.2, 0.4 and 0.6 m/s. The simulation results show that the greatest pressure loss occurs at a fluid velocity of 0.6 m/s where the flow is stratified mixed. While the smallest pressure loss at a mixture velocity of 0.2 m/s when the flow is stratified smooth. From the results of the study, it can be concluded that the increase in fluid flow velocity has a positive correlation with the increase in the value of flow losses in the pipe.

Friction of Coated and Uncoated Rough Surfaces in Additive-Free and Fully Formulated Engine Oils Under Boundary and Mixed Lubrication Conditions

Abstract Downsizing in spark-ignited engines becomes one of the most effective concepts to achieve fuel economy and emissions requirements and drives operating conditions of major moving engine components into more mixed and boundary lubrication regimes. Piston ring design faces considerable challenge to reduce friction losses, oil consumption, blow-by, and wear. Surface coatings have received great attention in applications of automotive engine components due to their unique friction properties. In this study, an elastic–plastic contact model of rough surfaces with hard coatings is used to provide proper design of the ring coating thickness concerning the plasticity-yielding resistance of stiff coating. A diamond-like carbon (DLC) coating with surface hardness higher than current production ring coatings has been evaluated in additive-free base oil and fully formulated engine oil under boundary and mixed lubrication conditions. The friction behavior of the coated material relative to uncoated materials is compared in boundary and mixed lubrication regimes. A traction-merging rolling speed in the mixed lubrication regime is observed, at which friction coefficient is independent of applied loads. By using a mixed lubrication model previously published, calculations indicate that the lower the traction-merging rolling speed, the earlier the contact approaches elastohydrodynamic lubrication (EHL), therefore reducing the risk of asperity-interacting fatigue in boundary and mixed lubrication regimes. Effects of tribofilm on friction behavior for DLC coating and uncoated steel in fully formulated oil are investigated by using measured Stribeck curves in conjunction with the model. The results from this study analytically support one of the possible mechanisms of tribofilm-dependent friction enhancement in mixed lubrication conditions proposed in the earlier publication.

Investigation of energy losses of the internal combustion engine taking into account the correlation of the hydrophobic and hydrophilic

Currently, numerous methods are introduced to reduce the loss of mechanical energy of the engine using various materials for anti-wear coatings. The paper presents the results of measurements of the motor torque for 18 multilayer AlN/CrN (20–30N2) and CrN/AlN (20–30N2) coatings. The coatings were applied in an Ar/N2 plasma environment with a variable N2 flow rate by reactive magnetron sputtering. The results were compiled for two oil temperatures, 80 and 100 °C, in the engine speed range from 800 to 4000 rpm. The test results show that highly hydrophilic coatings reduce the loss of mechanical energy of the engine in the lower engine speed range and in the oil environment with a high 4% soot content. Highly hydrophobic coatings enable the reduction of torque and resistance to movement of the engine for higher speed ranges, above 2000 rpm. This work is the first work that indicates the need to take into account hydrophilic and hydrophobic properties coatings in determining engine energy losses. The influence of these properties is much greater than the surface texture of the coatings, hardness, Young's modulus and other parameters of the coatings. It is a new look at the issue of reducing friction losses in the engine.

Nanoparticle Additives for Improving Lubricant Performance

The lubricant is an important industrial product widely used in vehicles and other machines. The main purpose of a lubricant is to reduce friction loss and save energy. However, with the development of the vehicle, the appearance of electrical vehicles, for example, and machines, lubricants need to satisfy more demands. Normally, this was fixed by adding additives. Nanoparticles are one of the best additives because they can efficiently reduce friction loss and provide a more useful function. But nanoparticles may form sedimentation in lubrication, which will increase friction loss and cause damage. Common methods like stirring, ball milling, and chemical methods are used in lab production to keep particles stable in lubricant. All those methods can form relatively stable samples of nano lubricants, but it is still hard for industrial manufacturers because of the technology blank and high cost. Nano lubricant is a potential market and can save more energy in the future.

Minimum Friction Losses in Planetary Stages of Wind Turbine Gearboxes

Mechanical efficiency is not a critical design factor of wind turbine gearboxes since wind energy is abundant and costless. The design and sizing of the gears will be determined by the requirements of power density, gear ratio, fatigue safety, and allowable noise and vibration levels. However, reducing power losses results in lower lubricant heating, and therefore, a smaller cooling system is required with lower induced thermal stresses. Reducing friction losses will therefore be beneficial for the mechanical behavior of the gearbox. This paper provides a new method for the calculation of the optimal values of the outside radii and rack shift coefficients of planetary gear stages to minimize the friction power losses, maintaining unalterable geometrical and operating parameters that ensure the preestablished values of the aforementioned critical design factors.

A Double FBGs Temperature Self-Compensating Displacement Sensor and Its Application in Subway Monitoring.

In order to ensure the effective vibration–reduction and vibration–isolation of the steel spring floating plate rail and meet the safe operation requirements of the subway, a Fiber Bragg Grating (FBG) displacement sensor for the deformation monitoring of the subway floating plate is proposed. The sensor adopts double FBGs to realize temperature self-compensation. The elastic ring is used as the elastic conversion structure after the fiber grating is pre-stretched; the two ends are pasted and fixed in the groove in the diameter direction of the ring, which avoids the waveform distortion caused by the full pasting of the fiber grating. The combination of linear bearing and displacement probe rods can increase stability and reduce friction loss so that the sensor has the advantages of high sensitivity and accurate measurement results. The test results and error analysis show that in the range of 0~20 mm, the sensitivity of the sensor is 164.2 pm/mm, the accuracy reaches 0.09% F.S, and the repeatability error and hysteresis error are only 1.86% and 0.99%, respectively. The thermal displacement coupling experiment proves that the sensor has good temperature self-compensation performance. It provides a new technical scheme for the effective monitoring and condition assessment of the built-in steel spring floating plate rail.

EVALUATION OF THE RATIOS OF THE MAIN INDICATORS OF THE DRY SEALING OF THE CYLINDER-PISTON GROUP OF INTERNAL COMBUSTION ENGINES USING A SOLID LUBRICANT

This article presents the results of a study of an alternative method for reducing friction losses in the cylinder-piston group of internal combustion engines based on an experimental installation, taking into account changes in the real state of the working surfaces of the mating parts of the piston ring-cylinder pair depending on the operating time. The factors with a progressive effect on the operation of engine friction units as they wear out are studied, and the degree of their influence on wear is estimated. A model of the friction unit of a cylinder-piston group (piston-piston ring pair) of an internal combustion engine based on a solid antifriction material operating without the use of a lubricating fluid is developed and investigated. Comparative results of determining the wear indicators of sealing rings by various methods of wear control are presented. A method for predicting the resource and the real state of the engine is proposed.

Optimizing the fuel efficiency of an opposed piston engine for electric power generation

This paper investigates the optimal crankshaft motion for an opposed piston (OP) engine in a novel hybrid architecture to maximize fuel efficiency. The OP engine was selected for this work due to its inherent thermodynamic benefits and the balanced nature of the engine which can achieve downsizing through reducing the number of cylinders rather than the individual cylinder volume. The typical geartrain required on an OP engine was exchanged for two electric motors, reducing friction loss and decoupling the crankshafts. Using the motors to control the crankshaft motion profiles, this architecture introduces capabilities to dynamically vary compression ratio, combustion volume, and scavenging dynamics. To leverage these opportunities, an optimization scheme was developed utilizing nonlinear optimization of a 0-D model to compute the crankshaft motion profile that maximizes the work generated by the system. This optimization was then iteratively coupled with a high fidelity model which supplies the cylinder flow boundary conditions. This iterative approach reduces the model complexity used in the optimal control problem (OCP) while capturing the gas exchange dynamics critical to the 2-stroke cycle of the OP engine. By using the rate of change of motor torque as the input to the OCP, the torque fluctuation in a single cycle can be limited to ensure tracking feasibility. The results show crankshaft velocity slows during the compression stroke and conversely accelerates during the expansion stroke, reducing the peak motor torque required for control and thus reducing the motor losses. The extended residence time at top dead center, however, leads to an increase in heat transfer, illustrating the trade-off between the work extraction efficiency and the indicated engine efficiency.

Experimental Characterization of a Foil Journal Bearing Structure with an Anti-Friction Polymer Coating

The development of highly efficient and environmentally friendly machines requires the use of new technologies that are created using innovative design solutions and new materials. This also applies to various types of propulsion units, such as gas microturbines or combustion engines. Although these machines have been known for many years, by using new components, it is still possible to improve their performance. This article presents an experimental study conducted on a gas foil bearing using a polymer coating as an anti-friction material. These types of bearings allow for a reduction in friction losses and are not lubricated with conventional lubricants. The dynamic characteristics of the foil bearing structure were determined, which are essential in terms of both rotor dynamics and the entire propulsion system. The research was carried out over a wide range of frequencies, with different loads acting in different directions. Hysteresis loops and vibration orbits were determined. The authors showed that displacements perpendicular to the load in some cases may be relatively large and should not be ignored. The results obtained during the tests can be used to validate numerical models of such bearings, optimize their design and select the structural and anti-friction materials.

Thermal Performance of Double-Sided, Partial Height Strip Fin Arrays in a High Aspect Ratio, Rectangular Channel

Abstract Friction loss and heat transfer enhancement measurements were obtained for double-sided, partial height, strip fin arrays in a high aspect ratio (AR = 8), rectangular channel. Fins were arranged in a staggered array configuration with channel height to fin thickness ratio H/W = 9.6, spanwise spacing distance to fin thickness ratio S/W = 8.0, and streamwise spacing distance to fin length ratio X/L = 1.0. Within the channel, shortened strip fins of equal length are positioned directly opposite to each other on two heat transfer surfaces with three gap size to channel height ratios considered G/H = 0.2, 0.3, and 0.4, respectively. The thermal performance of each fin configuration is determined from the measured pressure drop across the array and regionally averaged heat transfer coefficients at flow Reynolds numbers ranging Re = 20,000–80,000. Partial height strip fin results are compared to the baseline cases of full height strip fins and the smooth channel. Correlations of friction loss, heat transfer enhancement, and thermal performance are provided as functions of flow Reynolds numbers for all cases. Full height strip fins provide the greatest heat transfer enhancement of all cases but introducing a gap size can significantly reduce friction losses. The thermal performance is greatest when using full height strip fins for Reynolds numbers ranging Re = 20,000–30,000 and using partial height strip fins with the gap size of G/H = 0.3 for Re = 40,000–80,000.

MATHEMATICAL STUDY OF THE INFLUENCE OF KNIFE GEOMETRY WITH ARC-LIKE CROSS-SECTIONAL SHAPE ON THE PROCESS OF LONGITUDINAL FELT CUTTING

A promising study is the design and improvement of machines for longitudinal cutting of materials with minimal energy costs to perform the technological process of cutting due to the geometry of the cutting tool. The article considers the issues of reducing energy costs for the process of longitudinal cutting when using a knife blade with an arcuate cross-section. The analysis is carried out, the effective method of the analysis of influence of size of a backlash between generators of transporting rollers and size of distance from a vertical axis of rotation of transporting rollers to an edge of a knife blade with an arc-shaped cross section on the total size to determine the necessary settings in the machine of longitudinal cutting for felt, as well as to verify the reliability of analytical and experimental models of the process of longitudinal cutting with a knife with an arcuate cross-sectional shape. To determine the total amount of losses during longitudinal cutting of the material and the number of losses due to friction of the material on the face of a fixed knife with an arcuate crosssectional shape, as well as linear cutting force, a two-factor experiment was conducted for the study model. The obtained regression equations describe the total amount of losses during longitudinal cutting of the material and the number of losses due to friction of the material on the face of a stationary knife with an arcuate cross-section, suggest the adequacy of analytical and experimental models made earlier. Also make the necessary adjustments, namely, to adjust the degree of compression of the material and set the edge of the knife blade relative to the vertical axis of the transport rollers to reduce friction losses on the edge of the knife, which in turn reduces energy costs for longitudinal cutting. Comparing the total values of losses in the longitudinal cutting of the material of a knife with one-sided sharpening and a knife with an arcuate cross-section, allows you to talk about the feasibility of using a knife with an arcuate cross-section, which will reduce energy costs for the process.

Thermal Friction Characteristics of Engine Elements - Boundary Lubrication of Cam and Tappet

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 tribo-film low in shear stress, and the strength of interface materials are all under the influence of the exponential function of temperature, just like the Arrhenius’ equation. The results of the analysis found that the frictional shear stress changes depending on the intensity of involvement of surface temperature that affects oil viscosity, molecular adsorption / desorption and tribo-film formation in each running-in term.