Friction Power Loss Research Articles

Evaluation of Energy Losses in Auxiliary Systems and Mechanisms Subject to Friction in a Stationary Diesel Engine

This research has developed a methodology to estimate energy losses associated with auxiliary systems and mechanisms subject to friction in a stationary diesel engine. The study methodology is based on mathematical models used to calculate engine friction forces and power losses. The analysis involves the cooling, the lubrication, the fuel injection system, and the engine's valve train, bearings, and piston mechanism. A stationary diesel engine with four load conditions and three rotational speed conditions has been taken as a reference for the study. The analysis of the results has showed that fuel injection is the auxiliary system with the highest energy consumption. In general, the cooling system, the lubrication, and the injection represent loss energy equivalent to 0.3%, 0.5%, and 0.9% of the chemical energy of the fuel. The interaction between the cylinder liner and the piston skirt is the main source of energy loss associated with friction processes. For valve train mechanisms, bearings and pistons it has been evidenced that these represent 1.25%, 1.91%, and 5.26% of the chemical energy of the fuel. In general, the methodology proposed in this research is a tool that allows diagnosing energy losses in auxiliary systems and engine mechanisms, which is useful for evaluating future strategies focused on energy improvement.

Tribological evaluation of piston ring/cylinder liner assembly in automotive engines using GNP as a lubricant additive

Friction and wear are the main causes of energy dissipation in automotive engines. To minimize the frictional power losses, it is extremely important to improve the tribological characteristics of ring/liner assembly which accounts for almost 40–50% frictional power losses. The present study attempts to mitigate friction and wear of the ring/liner tribo-pair using GNP/SAE 15W40 nano-lubricant. To simulate the ring/liner interface, the tribological performance of nano-lubricants was assessed using a tribometer based on ASTMG181 standard under various operating conditions. The coefficient of friction (COF) and wear rate lowered using graphene nano-lubricants (GNL). The tribological results showed that friction coefficient, wear rate, and surface roughness of piston ring improved in the range 17.71%–42.33%, 25%–40.62%, and 61%, respectively, under GNL lubricating conditions during the boundary lubrication. Further, the characterization of wear tracks of piston ring and cylinder liner confirmed tribo-film formation on worn surfaces resulting in decreased COF and wear rate.

A new approach for modeling and analysis of the lubricated piston skirt-cylinder system with multi-physics coupling

The lubrication of the piston skirt-cylinder interface involves multiple physical fields, and these physical fields are coupled. A new method is proposed in this study for modeling and analysis of the lubricated piston skirt-liner interface with multi-physics coupling. This method is implemented in COMSOL Multiphysics software by coupling the heat transfer of the cylinder and piston, multibody dynamics of the crank-connecting rod-piston-cylinder system, the hydrodynamics lubrication of the skirt-cylinder interface, the thermal and elastic deformation of the piston-cylinder system, as well as the rheological properties of lubricating oil. The proposed method is first validated with a previous method and then adopted to a four-stroke gasoline engine to predict its dynamics and tribological characteristics. Then, a case study of different skirt thicknesses is conducted to reveal the influence the stiffness of the piston skirt exerts on the tribo-dynamics performance of the piston-cylinder system. The results indicate that although a thinner skirt will affect the stability of piston motion and increase the slapping noise and wear, it will benefit hydrodynamic lubrication between skirt and cylinder and reduce friction power loss.

A New Approach for Modeling Mixed Lubricated Piston-Cylinder Pairs of Variable Lengths in Swash-Plate Axial Piston Pumps.

The swash-plate axial piston pump is one of the most widely used pumps due to its simplicity and compactness in structure. In such a pump, the piston-cylinder system plays a crucial role, with its lubrication characteristics greatly affecting the overall pumping performance. A new numerical approach is proposed in this study for modeling mixed lubricated piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps in the framework of multibody dynamics. The approach couples the hydrodynamic mixed lubrication model of the piston-cylinder interface with the multibody dynamics model of the piston pump. The lubrication model is established with a transient average Reynolds equation considering asperity contacts and is solved with the finite element method to derive the hydrodynamic forces of the lubricated pair, while the multibody dynamics model is established with Lagrangian formalism by considering hydrodynamic forces as external forces. Results for piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps are presented, and the impacts of cylinder length and the tilt angle of the swash plate on the tribological performances of the interface are discussed. The results indicate that increasing the cylinder length can improve the stability and wear resistance of the piston, but it can exacerbate the frictional power loss. Moreover, although enlarging the tilt angle of the swash plate can effectively increase pump displacement, it can easily lead to serious friction, wear, and leakage problems. Consequently, the tilt angle of the swash plate should be carefully selected in practical applications.

Research on the influence of key structural parameters on piston secondary motion

Piston secondary motion not only influences the side knocking of piston and frictional loss, but also influence the in-cylinder oil consumption and gas blow-by. An inline four-cylinder common rail diesel engine was chosen as the research object. Dynamic simulation model of piston assembly was built based on the piston and cylinder liner temperature field test. The impacts of pinhole offset, liner clearance and piston skirt ovality on piston secondary motion were researched. Based on the surface response method, the influence of multiple factors on friction power loss and slapping energy is estimated. The results indicate that: in-cylinder stress condition of piston will change with its structural parameters, then the secondary motion of piston will be affected as a result. Pinhole offset, liner clearance, piston skirt ovality and the interaction of the latter two all have significant effects on the friction power loss, while the slapping energy is significantly affected by liner clearance. Therefore, the parameters can be designed based on the significance level to optimize the secondary motion characteristics of the piston.

Study on Lubrication Efficiency and Friction Power Loss of Engine Based on a Hybrid Hydrodynamic Model

Friction loss is one of the main factors affecting engine power. Reducing friction power losses to improve the power of engines is a significant concern for designers. Especially, under the background of energy-saving and emission reduction, it is indispensable to carry out an in-depth investigation on engine bearing lubrication characteristics. Unlike the previous studies of separate modelling, a new modelling method of coupling the dynamic and lubrication model is proposed in this paper. The bearing capacity, friction force, friction coefficient and eccentricity ratio were taken as the evaluation criterion, and the influence of design parameters such as angular speed, bearing radius and width on the lubrication efficiency and friction power loss (LE-FPL) were studied. The results indicate that increasing the angular speed, bearing radius or width can effectively reduce the eccentricity ratio and raise the minimum oil film thickness, which is beneficial to improve the lubrication efficiency. However, the above methods to improve engine lubrication efficiency will lead to more power loss of engine to a certain extent. Therefore, studies on reducing the friction power loss for the engine and on improving the lubrication efficiency for the engine should be considered coordinately in the dynamic design and optimisation of the engine.

Brush seal contact force theory and correlation with tests

Brush seals are leakage performance systems that are operating against turbine shafts and bucket tips. Flexible bristle structure can compensate the rotor interference during transients, which enables closer clearance control in turbine and turbo-engine applications. During turbomachinery transients, contacting bristles exert force on turbine shaft, which in turn result in wear, frictional heat generation, counter torque and power loss. Brush seal design with proper stiffness has crucial importance since high bristle tip force levels during rotor contact may result in rotor instability, bristle tip melting or thermo-mechanical fatigue due to large amount of local frictional heat input. Counter torque applied by the contacting brush seal with improperly excessive tip force may result in turbine stall and overall efficiency losses. High levels of bristle contact forces may induce elevated wear rates, which degrades the leakage performance of the brush seal during its life cycle. Brush seal contact force evaluation under operating conditions has critical importance and has to be conducted before turbine integration to avoid performance losses and possible turbine failure in some extreme cases. In this paper, ‘Bristle Contact Force Theory’ is developed and closed form bristle tip force (BTF) function is derived where rotor-bristle, inter-bristle and bristle-back plate interactions are included. BTF measurements under pressurized and unpressurized air environment are conducted for the selected test seals by using the custom ‘Rotary Test Rig’. BTF function of bristle contact force theory show high level of correlation with the test data. The effect of cant angle manufacturing tolerance on bristle tip force levels is also examined through bristle tip contact force theory, and compared with the test seal measurements. Methodology for number of bristle row calculation and comparison with the geometric inspection of test seals are also detailed within the content of this paper.

A Study on the Flow Resistance of Fluids Flowing in the Engine Oil-Cooler Chosen

Oil-coolers are necessary components in high performance diesel engines. The heat removed by the cooler is a component in the total heat rejection via the engine coolant. Oil-cooler absorbs the heat rejected during the piston cooling and engine rubbing friction power loss. During flows of both coolant and engine oil via the oil-cooler, some flow resistances occur. The aim of the study is to determine values of the flow resistance coefficient for oil going through the cooler at various temperatures. The test stand was developed to determine time needed to empty tanks from liquids flowing through oil-cooler. The flow model was elaborated to study the mentioned flow resistance coefficient with respect to changing liquid temperature. The 20 °C increase in liquid temperature resulted in a flow resistance coefficient decrease of 30% for coolant and of the much more for engine oil. It was found that better results would be achieved with flows forced by means of pumps instead of using gravitational forces on the test stand.

Analysis of lubrication and sealing performance on textured piston pair with multi-factor coupling

PurposeThis paper aims to study the lubrication and sealing performance on the textured piston pair under the cross action of the shape and structure parameters. This paper further carries out the optimization design of low energy consumption hydraulic impact piston pair.Design/methodology/approachBased on the characteristics of the ring gap seal piston pair, the flow field analysis model of the whole film gap is established for its periodic treatment. The friction power loss of the piston pair is defined as the evaluation index of the lubrication performance and the leakage power loss as the evaluation index of the sealing performance. The orthogonal test design and CFD software were used to analyze the lubrication and sealing performance of the textured piston pair.FindingsThe cross action of shape and structure factors has a great influence of the lubrication and sealing performance on the textured piston pair. Clearance and shape parameters have great influence on it, while seal length and depth diameter ratio have little influence. The sealing performance of conical textured piston pair is good, while the lubrication performance of square textured piston pair is good. The primary and secondary order of influence of shape and structure on energy consumption on piston pair is B (seal clearance) > C (texture shape) > D (area ratio) > A (seal length) > E (depth diameter ratio).Originality/valueBreaking the defect of local optimization design on traditional piston pair structure, then find the matching relationship of structural parameters on textured piston pair. Further improve the lubrication and sealing performance of the piston pair, and provide reference for the global optimization design of the low energy consumption hydraulic impact piston pair.

Study on Static Characteristics of Water-Lubricated Textured Spiral Groove Thrust Bearing Using Laminar Cavitating Flow Lubrication Model

Abstract Water-lubricated hydrodynamic spiral groove bearing is a potential support way for high-speed rotary machine, but the frictional power loss of the bearing will increase with the rotatory speed. Surface texture processing should be an effective technical means to decrease the friction power loss, and other static characteristics of the bearing will be affected by the such textural surface. However, the static characteristics of water-lubricated textured spiral groove thrust bearing have not been thoroughly considered. This article aims to establish the theoretical model for the water-lubricated textured spiral groove thrust bearing under laminar cavitating flow, and field distribution and static characteristics of the bearing are analyzed using the model. A verified test indicates that the theoretical simulation agrees with the experimental value. The result shows that, with consideration of texture effect, the friction torque of the bearing is reduced, there exists an optimal texture parameter for a given film thickness, under which the bearing has the maximum load-carrying capacity, no obvious change rule is found for the volume flowrate; with consideration of the cavitation effect, the load-carrying capacity of the bearing is increased, while the volume flow and the friction torque are slightly affected. The model developed in this study lays a solid foundation for the design of the water-lubricated textured spiral groove bearing.

Performance of textured spherical thrust hybrid bearing operating with shear thinning and piezoviscous lubricants

Improving the lubricating performance of tribo-pairs using engineering textured surfaces has been the main focus of tribology research in recent years. The use of a suitably designed micro-texture on the bearing surface may have a beneficial effect on the performance of fluid film bearings. In the present paper, a mathematical model of a hybrid spherical thrust bearing is developed considering the effect of shear thinning and piezoviscous behaviour of a lubricant. The modified Reynolds equation for a hybrid spherical thrust bearing configuration together with a restrictor flow equation for a capillary restrictor is solved using a finite-element method. In this work, the effect of various micro-textures shapes (spherical, circular, conical and square) and non-Newtonian lubricant behaviour having shear thinning and piezoviscous effects are analysed. The numerically simulated result shows a strong dependence on the combined effect of shear thinning and piezoviscous lubricant behaviour and a chosen geometric shape of a texture. The frictional power loss is seen to reduce nearly by 24.05%, and the stiffness gets enhanced by 11.08%.

Shift quality optimization control of power shift transmission based on particle swarm optimization–genetic algorithm

A clutch control strategy is proposed to improve the shift quality of power shift transmission and solve the power cycle phenomenon in the shifting process. The strategy effectively avoids the power cycle phenomenon by analyzing the change in the transmission torque and the relationship between the rotating speed of the driving and driven disks of a shifting clutch. The evaluation indexes of the shift quality of power shift transmission are sliding friction power loss, impact degree, and torque oscillation amplitude. Particle swarm optimization (PSO), combined with a genetic algorithm, is used to optimize the shift quality of power shift transmission, solving the problem in which basic PSO frequently converges to the local optimal solution. Simulations and experiments are performed on the optimization results. The simulation and test results show that the proposed control strategy can ensure that the rotating speed of the driving disk is always higher than that of the driven disk when the clutch is insliding and wearing states. Thus, this control strategy effectively avoids power cycle when shifting and improves shift quality.

Ferrofluid Lubrication of Optimized Spiral-Grooved Conical Hybrid Journal Bearing Using Current-Carrying Wire Model

Abstract To systematically investigate the behavior of fluid film bearing, the determination of optimal parameters is of utmost importance. The core contributions of this article are as follows: (1) modeling of the conical bearing for spiral grooves with ferrofluid lubrication using current-carrying wire model for the fixed coordinate system, (2) deriving the expressions for the magnetic field model and frictional power loss other than Reynolds equation for ferrofluid lubrication, and (3) evaluation of optimal values of spiral-grooved bearing surface for different cross-sectional shapes and that of the current-carrying wire model for magnetic field generation in ferrofluid lubrication. The generalized minimum RESidual iterative solver and the Newton–Raphson method have facilitated the solution of complex nonlinear finite element (FE) formulated governing equations. Initially, the results have been obtained for determining the optimal values of spiral groove and ferrofluid model attributes. After that, using these optimal values, corresponding performance indicators are evaluated. It was found that there exists a optimum value of different geometric features for distinct cross-sectional shapes of spiral grooves.

Lubrication characteristics study of main bearings on crankshaft balance rate

Unbalanced inertia force and moment of crankshaft generated by cylinder pressure have a significant effect on the vibration characteristics of diesel engine, but the study on the lubrication characteristics of crankshaft by balance rate needs to be studied. Based on Greenwood-Tripp asperity contact theory and average Reynolds equation, an elastohydrodynamic (EHD) lubrication model of the main bearing for a V-12 diesel engine is developed, and the influence of different balance rates on lubrication characteristics is analyzed. On this basis, a factorial experiment of ten influencing factors including the balance rate is designed, and the factors that significantly affected the lubrication characteristics of the main bearing are screened out by factor effect diagram, statistical analysis and residual probability diagram. The results show that the crankshaft with different balance rate has a great influence on the lubrication performance. With the increase of balance rate, the minimum oil film thickness first increases and then decreases, and the maximum oil film pressure first decreases and then increases. The balance rate, bearing width, bearing clearance, bush repair and oil viscosity have significant effects on the performance of main bearing, among which the balance rate of crankshaft has the greatest effect on the minimum oil film thickness, the maximum rough contact pressure and the average friction power loss.

Investigation of the effect of contact pattern design on the mechanical and thermal behaviors of plastic‐steel helical gear drives

This article describes an investigation that has been conducted to assess the effects of the contact pattern design on the mechanical and thermal behaviors of plastic-steel helical gear drives. The maximum contact pressure, frictional power loss, transmission error function and operating temperature are determined for different designs of the pinion tooth surfaces. Several numerical examples based on loaded tooth contact analyses and steady-state heat transfer analyses are carried out considering different types of micro-geometry modifications of the involute tooth surfaces. The obtained results show that an appropriate design of the pinion tooth surfaces can help reducing the maximum contact pressure and the maximum operating temperature, increasing the durability of the transmission. The frictional power loss and the peak-to-peak transmission error can be diminished, improving the performance of the transmission and increasing its efficiency. Also, it has been shown that the design of the pinion tooth surfaces can provide some capability to the transmission to absorb angular misalignments.

Design and Optimization of a High-Speed Permanent Magnet Synchronous Machine for Gas Compressors

In this article, a high-speed permanent magnet synchronous machine (PMSM), which is rated at 15 kW and 120 krpm for a gas compressor, is designed and optimized. According to the design specifications, two design schemes of different rotor topologies are presented and compared by the finite element method (FEM) to determine the preliminary scheme of the original machine. The performance of the original machine is obtained by FEM. Meanwhile, the losses of the original machine are analyzed and calculated for optimization. Especially, the conductor diameter of the winding is selected to reduce the copper loss of the machine. Finally, in order to reduce wind friction loss and increase power density, the dimensions of the stator core and the thickness of the permanent magnet (PM) are optimized. Compared with the original model, the wind friction loss is reduced by 17.2%, and the power density is increased by 6.64% in the optimized machine.

Improving frictional performance of ring-liner system under cylinder deactivation conditions by surface texturing

In this study, a method of surface texture is considered to improve the frictional performance of the ring-liner system (i.e. RLS) under the conditions of cylinder deactivation (i.e. CDA). To assess the effectiveness of the method, a lubrication model is developed with considerations of the liner deformation, the actual rheological properties of lubricant, and the lubricant transport. By solving the model numerically, the friction reduction effect of surface texture for the RLS under the CDA is investigated. The results show that the surface texture can improve the friction properties significantly. For a six-cylinder gasoline engine, 7.57% and 7.28% decreases in the total average friction loss and power loss are observed when the RLS under the CDA is surface textured.

The Effects of Ultra-Low Viscosity Engine Oil on Mechanical Efficiency and Fuel Economy

The development of a sustainable powertrain requires improved thermal efficiency. Reducing frictional power losses through the use of ultra-low viscosity oil is one of the most effective and economical ways. To assess the potential for efficiency enhancement in a new generation of future engines using low-viscosity oils, a technical analysis was conducted based on numerical simulation and theoretical analysis. This study proposes a numerical method coupling the whole multi-dynamics model and lubrication model under mixed lubrication regimes. Then, load distribution was calculated numerically and verified experimentally. Finally, this paper compares the bearing load and frictional energy loss of the main bearings when using The Society of Automotive Engineers (SAE) 15W40 and SAE 0W20 oil. The results indicate that the application of ultralow-viscosity lubricant can reduce the hydraulic friction loss up to 24%, but the asperity friction loss would increase due to the reduction in load capacity. As a result, the design of a new generation of high efficiency internal combustion engines requires careful calculation and design to balance the trade-off relations between hydraulic friction and asperity friction.

Effect of shape/size and distribution of microgeometries of textures on tribo-performance of crankpin bearing

The effect of the shape/size and distribution of microgeometries of textures on improving the tribo-performance of crankpin bearing is proposed. Based on a combined model of the slider-crank mechanism dynamic and hydrodynamic lubrication, the distribution density, area density, and shape of spherical textures, square-cylindrical textures, wedge-shaped textures, and a hybrid between spherical texture and square-cylindrical texture on the crankpin bearing's tribo-performance are investigated under different operating conditions of the engine. The tribological characteristic of the crankpin bearing is then evaluated via the indexes of the oil film pressure p, asperity contact force, friction force, and friction coefficient of the crankpin bearing. The research results show that the distribution density with n = 12 and m = 6, and area density with α = 30% of various microtextures have an obvious effect on ameliorating the crankpin bearings tribo-performance. Concurrently, at the mixed lubrication region, the shape of the square-cylindrical texture on improving the tribo-performance is better than the other shapes of the spherical texture, wedge-shaped texture, and spherical and square-cylindrical texture. Particularly, all the average values of the asperity contact force, friction force, and friction coefficient with a square-cylindrical texture are significantly reduced by 14.6%, 19.5%, and 34.5%, respectively, in comparison without microtextures. Therefore, the microtextures of the spherical texture applied on the bearing surface can contribute to enhance the durability and decrease the friction power loss of the engine.

Research on different structures of dimpled textures on improving the LE-FPL of engine

PurposeThis paper aims to research the effect of the different structures of dimpled textures on the rod bearing surfaces on improving the engine’s lubrication efficiency and friction power loss (LE-FPL).Design/methodology/approachBased on the hydrodynamic model of the rod bearing, the effect of different structures of dimpled surfaces including circular dimples (CD), square dimples (SD), wedge-shaped dimples (WSD), circular-square dimples (CSD) and square-wedge-shaped dimples (SWSD) on ameliorating the LE-FPL is analyzed under the different operating conditions of the engine. The oil film pressure (p), asperity contact force (Wac), friction force (Ff) and coefficient of friction (COF) of the rod bearing are chosen to evaluate the LE-FPL.FindingsThe SD’s performance on improving the LE-FPL is better than all other structures of the CD, WSD, CSD and SWSD. Particularly, the average values of Wac, Ff and COF with the SD is significantly reduced by 14.5%, 28.5% and 33.3% compared to the optimal dimensions of the rod bearing; and by 26.4%, 34.5% and 43.7% compared to the optimal CD (n = m = 6).Originality/valueThe generated friction between surfaces of rod bearings of the engine not only reduces the engine power but also affects the durability of the structures. Thus, the optimal design of the SD to further improve the LE-FPL is very necessary.