Search

The stuffing box-piston rod system is widely used in the low-speed marine diesel engines to scrape oil and ensure sealing. Its friction power loss and wear rate are great, but the studies about the system are very limited. In this study, based on the special structure and working conditions of the stuffing box, the analytical model for the tribological properties of the stuffing box-piston rod system is developed considering the oil starvation and relative ring location effects. The minimum oil film thickness, friction, oil transportation, and asperity contact are calculated for the stuffing box. The analysis results show that compared with the fully flooded lubrication, the minimum oil film thicknesses of the rings reduce significantly in the middle of the strokes under the starved lubrication condition, but the friction losses of the rings are influenced by the comprehensive effects of the oil film thickness reduction and lubricating area reduction under the starved lubrication condition, which is related to the specific profiles of the rings. In addition, compared with the engine piston ring pack, the relative ring location effect is more obvious in the stuffing box ring pack because there are more rings and the ring intervals are larger. The relative ring location effect makes the minimum oil film thicknesses, friction forces, and asperity contacts of the rings have oscillations after bottom dead center and top dead center. [ABSTRACT FROM AUTHOR]

This article employs a mixed lubrication model to investigate the performance of the textured surface. The Jakobsson–Floberg–Olsson model is used to obtain the hydrodynamic support of the textured conjunction, while the calculation of the asperity contact load is based on the load-sharing concept. Based on the simulated Stribeck curves of the smooth surface and the textured surface, comparisons are conducted to study the effect of texturing under different lubrication regimes. It appears that the transition of lubrication regimes is influenced by the texturing parameters and the convergence degrees of conjunction. The presence of textures delays the appearance of the mixed lubrication regime and the boundary lubrication regime. [ABSTRACT FROM AUTHOR]

The starved lubrication is common in engine. However, there are only few studies on starved lubrication problem for textured surfaces. In particular, for the textured surface, a two-dimensional solution is required to study their performances clearly, by considering the pattern and distribution of textured cells. This article presents a new analysis method for the two-dimensional starved lubrication problems with the textured surfaces. In the starved model, the inlet boundary condition of oil film is required and needs to be updated over the process of calculation. In order to obtain the inlet boundary condition, the flow conservation equations at the inlet region are built to determine the position of the attaching point. Meanwhile, as the two-dimensional code is expensive in the computational cost, the multigrid method is employed to accelerate the convergence of pressure. The inlet boundary condition should be transferred between the coarse grids and the fine grids. In this way, solutions for the starved lubrication are offered for an efficient implementation. The starved lubrication model is successfully applied in the ring–liner system. The effects of the surface features on the inlet boundary, wear and friction loss are discussed. It is found that the surface texturing can improve the performance of the ring–liner system under the staved lubrication. [ABSTRACT FROM AUTHOR]

To reduce the friction of a piston ring while maintaining a large oil film load-carrying capacity, an approach comprising of the inverse method and the sequential quadratic programming algorithm was proposed. The approach considers the variation of mixed lubrication and variable lubricant viscosity with temperature along the engine stroke, is developed to optimize the profile of a piston ring. A piston ring profile is represented by a polynomial function. A case study of the second piston ring shows that the proposed method can be applied for the optimization of a piston ring profile. In addition, this paper illustrates the effects of the degree of a polynomial function. The results show that the minimization of friction and maximization of oil film load-carrying capacity can be balanced simultaneously when the degree of the polynomial is 2 and 5. [ABSTRACT FROM AUTHOR]

In this study, the performance of surface texturing on nonflat surfaces is numerically investigated. A one-dimensional mixed-lubrication model considering the oil supply is employed. The cases of the nonflat ring lubrication with full and partial texturing are conducted in steady-state and engine-like conditions. By considering the oil transport for lubricant distribution along the liner, the simulation for the whole ring pack is also conducted. As a main conclusion, the textured surface can obtain a special benefit on the tribological properties under not only the mixed lubrication, but also starved lubrication. In addition, it also suggests that the reduction of the ring-pack friction is possible if the nonflat top compression ring is textured. [ABSTRACT FROM AUTHOR]

A theoretical analysis is presented for the mixed lubrication of the piston skirt-liner system. The model is developed to consider the shear thinning effect of multigrade lubricant. The friction characteristics of the piston skirt-liner system for both monograde and multigrade lubricants are investigated. It is found that a decrease in the lubricant viscosity is effective in reducing the friction loss. However, the boundary friction at the expansion stroke will increase with low lubricant viscosity. Results in this study show a significant lubricant shear thinning effect on the piston skirt-liner system. [ABSTRACT FROM PUBLISHER]

With the development of high-performance and high-speed engines, the effects that the connecting-rod-related design parameters have on the performance of the piston–liner system have become more important. Based on a new model of the piston dynamics presented by the present authors, the effects of the connecting-rod-related parameters on the side force, the oil-film thickness, the frictional force, and the piston dynamics are investigated. The results show that the changes in the extra transverse force and the piston’s secondary motion are the main reasons for the different performances of the system. When the mass and the rotational inertia of the connecting rod are decreased, the extra transverse force is significantly reduced. When the location of the center of mass of the connecting rod is changed, the extra transverse force obviously changes in amplitude and trend. When the length of the connecting rod is increased, the amplitude of the extra transverse force increases during the upper half-stroke near the top dead center and decreases during the bottom half-stroke near the bottom dead center. Because of these changes in the connecting rod, the change in the extra transverse force leads to different behaviors of the side force, the minimum oil-film thickness, and the piston’s secondary motion. However, changing the connection position of the connecting rod to the piston gives rise to very different behaviors of the piston’s secondary motion, and the change in the piston’s secondary motion generates significant differences in the minimum oil-film thickness. This study shows that the connecting-rod-related parameters are significant to the performance of the piston–liner system. [ABSTRACT FROM AUTHOR]

Robust and accurate measurement techniques are essential to studying the piston-assembly friction of Internal Combustion (IC) engines. Based on the instantaneous Indicated Mean Effective Pressure (IMEP) method, this paper develops an improved measurement technique to evaluate the piston-assembly friction in engines. Wireless telemetry technology is employed in the measurement of connecting rod axial force, which greatly minimizes the engine modifications and enhances the measurement stability compared to the conventional wired way. The measurement system, which is composed of computer, data acquisition system, sampling trigger apparatus and sensors, is exploited with special attention given to the sampling synchronization of signal channels including cylinder pressure, connecting rod force and crank angle position. Engineering implementations are carried out on a four-stroke gasoline engine under motored condition. The measurement results are compared with numerical results from a newly developed numerical coupling model system, and it shows that the two agree well. In addition, the piston-assembly friction under different engine speeds and inlet lubricant temperatures are also measured, and analyses indicate that these results are in good correlation with the well-known Stribeck curve. This improved measurement technique provides an accurate and reliable option for the friction evaluation of piston-assembly components in engine designs. [ABSTRACT FROM AUTHOR]

In this paper, considering the coupling effects of the crosshead slipper-guide system and the piston skirt-liner system, a new tribodynamic model is established for the low-speed two-stroke marine diesel engine. Firstly, a dynamic model including the crosshead slipper, the piston, the piston rod, and the crosshead pin is proposed. Then, considering the disciplinary coupling between the dynamic model and the lubrication models, the stiff and nonlinear tribodynamic model is solved with the modified extended backward differentiation formulae (MEBDF). Finally the tribodynamic performances of the crosshead slipper and the piston skirt are analyzed. The simulation results show that the crosshead slipper bears the thrust force and its friction power loss is obviously larger than that of the piston skirt. [ABSTRACT FROM AUTHOR]

“Zero-wear” is considered as wear within the limits of surface topography of the component. The honed cylinder liner surface is composed of the plateaus and relatively deep valleys. In this paper, a two-scale homogenized mixed lubrication and wear model is established to study the “zero-wear” process of the cylinder liner. In order to consider the plateau roughness and the valleys separately on local and global scales, the honed surface is firstly decomposed into plateaus and valleys by the morphological filtering approach. Then, based on two-scale homogenization technique, a homogenized mixed model is developed to characterize the lubrication properties and the contact severity of the piston ring-liner system. On this basis, the cylinder liner “zero-wear” process is divided into two stages: at the first stage, running-in of the plateau component on the local scale; at the second stage, wear of the valley component on the global scale. On the local scale, the influence of the plateau component running-in on the homogenized flow factors and contact stiffness is studied. On the global scale, the influence of the valley component wear on the lubrication properties (load carrying capacity, contact force and friction coefficient) is studied. Experiments are conducted on a reciprocating tester. The experimentally measured friction coefficient and wear depth are shown to be in good agreement with the simulation results. The results showed that the two-scale homogenized mixed lubrication and wear model developed in this paper can well predict the cylinder liner “zero wear” process. [ABSTRACT FROM AUTHOR]

In order to consider the effect of the local surface properties, such as textures and roughness, a mass-conserving model is specifically developed based on the Elrod–Adams model. The classic flow factor methodology is incorporated in this model to deal with the roughness scale. Meanwhile, by reformulating the cavitation conditions according the Fischer–Burmeisster equations, the system of discretized equations for this model is changed to be unconstrained. The computational efficiency of the developed model is similar to that when cavitation is not considered. Finally, this model is evaluated in the predicting the performance of the textured ring/liner system under the start-up process. [ABSTRACT FROM AUTHOR]

In this paper, a semi-deterministic analytic thermal solution is presented for the rough textured ring/liner conjunction. The energy equation is employed to reveal more detailed information about the tribological performance of the textured surfaces in terms of the thermal effects and the viscosity change. The effects of surface texturing under the cold and warm engine conditions are studied over a wide range of engine speeds. It is shown that the thermal effects play a crucial role in hydrodynamic lubrication, particularly under the cold start condition. Including the thermal effects in the numerical simulation can ensure the accurate predictions. [ABSTRACT FROM AUTHOR]

Well-designed surface texturing could reduce the ring/liner friction. However, so far most researchers have focused on the aspect of texturing under fully flooded lubrication. In this study, the performances of textures under starved lubrication are investigated. Specially for the textured ring/liner system, the flow conservation equations at the inlet region are built. In this way, the effect of the oil trapped in the texture features can be modeled clearly. The simulation results show that the textured liner can obtain a steady benefit on the tribological properties. However, the positive influence of the textured ring may remain unsteady under starved lubrication conditions. [ABSTRACT FROM AUTHOR]

• Measurement of piston-assembly friction under fired conditions is implemented. • The wireless IMEP method is applied to obtain the piston-assembly friction. • A measurement system is modified to meet the demands of an online test. • The lubrication and dynamic models are built for piston rings and piston skirt. • The measured results are compared with the numerical simulations. Reliable and accurate measurement of piston-assembly friction is urgently required in the field of internal combustion engines. With few modifications to the engine, an improved wireless instantaneous indicated mean effective pressure (IMEP) technique for measuring piston-assembly friction under fired conditions is first presented in this paper. The piston-assembly friction is obtained indirectly by measuring the cylinder pressure, the connecting rod force, the crank position and the engine speed under various conditions. A measurement system, mainly including a wireless rechargeable telemetry module, a data acquisition system and three typical sensors, is modified for an online test. After the in-situ measurement and the simulations, it is found that the simulation results generally coincide with the measured data. Though the current measurement technique still suffers from challenges in signal synchronization, noise control and system reliability, it can be applied for the direct performance evaluation of piston assembly in the future. [ABSTRACT FROM AUTHOR]