Computations and Modeling of Oil Transport Between Piston Lands and Liner in Internal Combustion Engines PDF Download
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Author: Tianshi Fang
Publisher:
ISBN:
Category :
Languages : en
Pages : 136
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Book Description
The consumption of lubricating oil in internal combustion engines is a continuous interest for engine developers and remains to be one of the least understood areas. A better understanding on oil transport is critical to an optimization of engine designs, and advanced analytical tools are essential to the achievement of reduced frictions without compromising oil consumption. Oil transport from piston lands to a liner, hereafter called "bridging", has been observed in engine tests. The additional oil transferred to the liner becomes a potential source of oil consumption through ring-liner interaction. Thus, it is important to develop more quantitative models to better analyze bridging. The objective of this work is to obtain a more in-depth understanding on the oil transport between piston lands and liner and provide quantitative models of the oil transport mechanisms. Multiphase Computational Fluid Dynamics (CFD) was employed together with analyses of experimental observations. Three categories of bridging were identified: assisted bridging, self-sustained bridging, and reverse bridging. While assisted bridging involves an axial oil flow across an entire piston land, the other two phenomena are localized and become prominent at low engine speeds. The mechanisms of each phenomenon were analyzed in this work. Correlations and theoretical models were developed to associate the risk of bridging with geometrical designs of a piston and operating conditions of an engine. Particularly, the theoretical model of self-sustained bridging contributes to the optimization of geometrical designs of the third land of a piston ring pack. This work constitutes a major step towards a further quantification of oil transport. Some findings and models presented in this work can readily contribute to providing optimal solutions to certain piston regions. Furthermore, the results of this work serve broader purposes in providing boundary conditions to other interactions in a piston ring pack.
Author: Tianshi Fang
Publisher:
ISBN:
Category :
Languages : en
Pages : 136
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Book Description
The consumption of lubricating oil in internal combustion engines is a continuous interest for engine developers and remains to be one of the least understood areas. A better understanding on oil transport is critical to an optimization of engine designs, and advanced analytical tools are essential to the achievement of reduced frictions without compromising oil consumption. Oil transport from piston lands to a liner, hereafter called "bridging", has been observed in engine tests. The additional oil transferred to the liner becomes a potential source of oil consumption through ring-liner interaction. Thus, it is important to develop more quantitative models to better analyze bridging. The objective of this work is to obtain a more in-depth understanding on the oil transport between piston lands and liner and provide quantitative models of the oil transport mechanisms. Multiphase Computational Fluid Dynamics (CFD) was employed together with analyses of experimental observations. Three categories of bridging were identified: assisted bridging, self-sustained bridging, and reverse bridging. While assisted bridging involves an axial oil flow across an entire piston land, the other two phenomena are localized and become prominent at low engine speeds. The mechanisms of each phenomenon were analyzed in this work. Correlations and theoretical models were developed to associate the risk of bridging with geometrical designs of a piston and operating conditions of an engine. Particularly, the theoretical model of self-sustained bridging contributes to the optimization of geometrical designs of the third land of a piston ring pack. This work constitutes a major step towards a further quantification of oil transport. Some findings and models presented in this work can readily contribute to providing optimal solutions to certain piston regions. Furthermore, the results of this work serve broader purposes in providing boundary conditions to other interactions in a piston ring pack.
Author: Camille Baelden
Publisher:
ISBN:
Category :
Languages : en
Pages : 218
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Book Description
Fuel consumption reduction of more than 20% can be achieved through engine friction reduction. Piston and piston rings contribute approximately half of the total engine friction and are therefore central to friction reduction efforts. The most common method to reduce mechanical losses from piston rings has been to lower ring tension, the normal force providing sealing between the piston ring and the cylinder liner. However tension reduction can result in additional lubricant consumption. The objective of this thesis is to understand and model the physical mechanisms resulting in flow of oil to the combustion chamber in order to achieve optimal designs of piston rings. The optimal design is a compromise between friction reduction and adequate gas and lubricant sealing performance. To do so a multi-scale curved beam finite element model of piston ring is developed. It is built to couple ring deformation, dynamics and contact with the piston and the cylinder. Oil flow at the interfaces between the ring and the cylinder liner and between the ring and the piston groove can thus be simulated. The piston ring model is used to study the sealing performance of the Oil Control Ring (OCR), whose function is to limit the amount of oil supplied to the ring pack. The contributions of the three main mechanisms previously identified, to oil flow past the OCR are quantified: - Deformation of the cylinder under operating conditions can lead to a loss of contact between the ring and the liner. - Tilting of the piston around its pin can force the OCR to twist and scrape oil from the liner. - Oil accumulating below the OCR can flow to the groove and leak on the top of the OCR The OCR is found to be flexible enough to limit the impact of cylinder deformation on oil consumption. Both ring scraping and flow through the OCR groove can contribute to oil consumption in the range of engine running conditions simulated. Reduction of scraping is possible by increasing the ability of both OCR lands to maintain contact with the liner regardless of piston groove tilt. The flow of oil through the OCR groove can be reduced by designing appropriate draining of oil in the groove and an adequate oil reservoir below the OCR. The piston ring oil transport model developed in this thesis will be a valuable tool to optimize ring pack designs to achieve further ring pack friction reduction without increasing oil consumption.
Author: Dongfang Bai (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 147
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Book Description
Ever-increasing demand for reduction of the undesirable emissions from the internal combustion engines propels broader effort in auto industry to design more fuel efficient engines. One of the major focuses is the reduction of engine mechanical losses, to which the friction of the piston skirt is one important contributor. Yet there lacks a sufficient understanding of the skirt lubrication behavior to effectively optimize the piston skirt system in practice. The ultimate goal of this work is to develop a comprehensive model to advance the predictability of the skirt friction while integrating all the dynamic behavior of the piston secondary motion and the structural deformation of the piston skirt and cylinder liner. Major contributions of this work are analysis of and development of a model for the oil transport and exchange of the piston skirt region and its surroundings. The new oil transport model is composed with two elements. First, the oil scraped into the chamfer region by the oil control ring during a down-stroke is tracked and its accumulation and release to the skirt region are modeled. Second, oil separation and re-attachment are allowed in the skirt region, breaking conventional full-attachment assumption in lubrication studies. The new oil transport model together with hydrodynamic and boundary lubrication model were coupled with piston secondary motion and structural deformation of the piston skirt and cylinder liner. For numerical efficiency and physics clarity, we used different discretization for the lubrication from the structural deformation. The final model is robust and efficient. The discussion of the model results is focused mainly on the oil transport. There exist a general pattern in available oil for skirt lubrication, namely, skirt tends to be starved when it travels at the upper portion of a stroke. Comparison with visualization experiment for oil accumulation patterns show consistency between model prediction and observation. This work represents a major step forward to realistically predicting skirt friction and the influence of all the relevant design and operational parameters. However, oil supply to the region below the piston skirt can largely influence the outcome of the friction prediction and its mechanism is system dependent. Additionally, simple treatment of the oil transport in the current model is merely a first step to modeling the complex fluid problems involved. Improvements of this model based on application and further analysis will make it a more powerful engineering tool to optimize the skirt system to minimize its undesirable outputs.
Author: Yeunwoo Cho
Publisher:
ISBN:
Category :
Languages : en
Pages : 172
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A model was developed to study engine oil vaporization and oil vapor transport in the piston ring pack of internal combustion engines. With the assumption that the multi-grade oil can be modeled as a compound of several distinct paraffin hydrocarbons, a set of equations governing the oil vapor density variations were derived by applying the mass conservation law to the amount of oil vaporized from the piston and the amount of oil vapor transported within the piston ring pack. The model was applied to a heavy-duty diesel engine. First, the case with the maximum oil supply to all the piston regions was studied and the results showed that, under this condition, the oil consumption from vaporization alone was far greater than the typical oil consumption value measured in the engine. Then, to show the contribution of oil vaporization to oil consumption and the dependence of vaporization on oil supply to different regions, different lubrication conditions for the high temperature regions of the piston were studied. Finally, a liquid oil transport model was integrated with this oil vaporization model in order to investigate the change of oil composition on the crown land with each engine cycle and the contribution of liquid-phase oil and vapor-phase oil to the total oil consumption under a fixed liquid oil supply rate to the crown land.
Author: Benoist Pierre Thirouard
Publisher:
ISBN:
Category :
Languages : en
Pages : 526
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(Cont.) Then, using the individual oil transport models, the contributions of the different oil transport mechanisms to oil flow in and between the piston regions and the effects of piston and ring designs were analyzed. Finally, a global oil transport scheme was presented by integrating all major paths and mechanisms of oil transport along the piston. It highlighted that the rate at which oil is lost to the combustion chamber is mostly determined by the competing oil transport processes occurring on the piston lands. While the effect of the inertia force results in a net oil flow toward the top of the piston, the dragging action of the blow-by gases removes oil from the piston lands and recycles it to the crankcase. This work was the first comprehensive investigation of the mechanisms of oil transport in the piston ring pack of internal combustion engines. It constitutes a major step in the development of analytical tools for oil consumption reduction.
Author: Sean William McGrogan
Publisher:
ISBN:
Category :
Languages : en
Pages : 136
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Carbonaceous deposits have long plagued the internal combustion engine, yet a fundamental comprehension of their underlying causes remains to be developed. In particular, piston land deposits can bring about an array of problems; for example, once a thickness threshold is crossed, the engine's reliability is threatened by an elevated possibility of seizure. As tightening emissions regulations continue to place more stringent constraints on power cylinder design, control of piston deposits, specifically in the top land and top ring groove, is becoming ever more difficult. Tests run on a heavy duty diesel engine revealed the piston land carbon deposit distribution to be circumferentially nonuniform, and a theoretical inquiry was invoked to investigate the cause. Since these deposits are typically lubricant derived, a three-dimensional, unsteady model of the oil film attached to a piston land was formulated. Focus was placed on the top land, in order to explore the effects of both reciprocating inertia and combustion-driven gas flows on the film's motion and thickness distribution. The numerical simulation created uses results from a realistic CFD simulation of the combustion process as input data. It was found that the gas velocities can have a profound effect. The gases create interesting wave structures on the free surface of the oil film, significantly altering the film thickness distribution. A new mechanism governing oil transport was discovered. Clever usage of this mechanism could substantially reduce the amount of oil, and hence the amount of deposit, on the top land. The simulation shows potential for application not only to the study of deposit formation, but also to that of oil consumption.
Author: Haijie Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 133
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Piston ring packs are used in internal combustion engines to seal both the high pressure gas in the combustion chamber and the lubricant oil in the crank case. The interaction between the piston ring pack and the cylinder bore contributes substantially to the total friction power loss for IC engines. The aim of this thesis work is to advance the understanding of the ring liner lubrication through numerical modeling. A twin-land oil control ring lubrication model and a top two-ring lubrication model are developed based on a deterministic approach. The models take into consideration the effect of both the liner finish micro geometry and the ring face macro profile. The liner finish effect is evaluated on a 3D deterministically measured liner finish patch, with fully-flooded oil supply condition to the oil control rings and starved oil supply condition to the top two rings. Correlations based on deterministic calculations and proper scaling are developed to connect the average hydrodynamic pressure and friction to the critical geometrical parameters and operating parameters so that cycle evaluation of the ring lubrication can be performed in an efficient manner. The models can be used for ring pack friction prediction, and ring pack/liner design optimization based on the trade-off of friction power loss and oil consumption. To provide further insights to the effect of liner finish, a wear model is then developed to simulate the liner surface geometry evolution during the break-in/wear process. The model is based on the idea of simulated repetitive grinding on the plateau part of the liner finish using a random grinder. The model successfully captures the statistic topological features of the worn liner roughness. Combining the piston ring pack model and the liner finish wear model, one can potentially predict the long term ring pack friction loss. Finally the thesis covers the experimental validation of the twin-land oil control ring model using floating liner engine friction measurements. The modeled ring friction is compared with the experimental measurement under different ring designs and liner finishes. The result shows that the model in general successfully predicts the friction force of the twin-land oil control ring/liner pair.
Author: Yang Liu (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 217
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Book Description
Improving fuel economy of internal combustion engines is one of the major focuses in automotive industry. The piston ring friction contributes as much as 25% of total mechanical loss in internal combustion engines [1] and is an area of great interests to the automotive industry in their overall effort to improve engine efficiency. However, typical methods to reduce friction loss from piston ring pack, such as ring tension reduction, may cause additional oil consumption. A compromise between reduction of friction loss and control of gas leakage and oil consumption needs to be made, which requires a deep understanding of oil transport mechanism. This compromise gives rise to the interest in modeling work. Both experimental results and previous experience showed that oil film distribution on the piston varies significantly along the circumference and the oil leakage occurs locally. Therefore to predict oil transfer across different ring pack regions, one needs to integrate both global and local processes. This work is aimed at establishing an enduring framework for all the cycle-based processes at different length scales. As a first step, a multi-scale multi-physics piston ring pack model was developed by coupling the structural dynamics of the piston rings with gas flows and local interactions at ring-groove and ring-liner interfaces. A curved beam finite element method was adopted to calculate the ring structural response to interaction between the ring and the liner as well as the ring and the groove. Compared to a traditional straight beam finite element method, the curved beam separates the structural mesh and contact grid by utilizing the shape functions. In this work, a multi-length-scale ring pack model was, for the first time, successfully assembled. This model bears its fundamental values to truly reflect the integral results of all the relevant mechanisms. The significance of the current work is that it demonstrated such an integration of all the length scales is possible for a cycle model with a reasonable computation cost. With the current model, one can realistically investigate the effects of all kinds of piston and liner distortion, piston secondary motion, bridging, and lube-oil dilution on gas sealing, oil transport and lubrication. As a result, optimization of the ring designs and the part of block design contributing to bore distortion can be coordinated to reduce development costs.
Author: Wang Zhang (S.M.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 98
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Book Description
Reducing emission and improving efficiency of internal combustion engines are the major focuses in modern automotive industry. Lubrication oil leakage contributes to particle formation and piston ring friction occupies 1/3 to 1/2 of total mechanical losses in engines. In almost all of modern gasoline engines, three-piece oil control ring (TPOCR) is used considering its low-cost and satisfying oil control performance in low load work conditions. While TPOCR will see high oil consumption at high load, high speed working conditions. This raises our interest in modeling work to predict the TPOCR dynamics and oil transport and explain the oil control mechanism. This master thesis work is focusing on building a three-piece oil control ring model coupling the oil transport. First, a 2D dynamics model for three pieces is established as the main frame. Second, oil transport in different zones will be modelled in different ways considering the length scales. Specially for the oil movement behind the ring, a novel approach is introduced by using neural networks to learn and run the reduced order modeling of computational fluid dynamics (CFD), to speed up the calculation. The model is then applied on a 2D laser induced fluorescence (2DLIF) engine and produces consistent simulation results with experimental observation. Further parametric study on oil transport will be discussed to build a complete picture of oil transport around TPOCR.
Author: Qing Zhao (S.M.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 88
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Book Description
When decreasing of fossil fuel supplies and air pollution are two major society problems in the 21st century, rapid growth of internal combustion (IC) engines serves as a main producer of these two problems. In order to increase fuel efficiency, mechanical loss should be controlled in internal combustion engines. Interaction between piston ring pack and cylinder liner finish accounts for nearly 20 percent of the mechanical losses within an internal combustion engine, and is an important factor that affects the lubricant oil consumption. Among the total friction between piston ring pack and cylinder liner, boundary friction occurs when piston is at low speed and there is direct contact between rings and liners. This work focuses on prediction of contact between piston ring and liner finish based on 3D measured surface and different methods are compared. In previous twin-land oil control ring (TLOCR) deterministic model, Greenwood-Tripp correlation function was used to determine contact. The practical challenge for this single equation is that real plateau roughness makes it unreliable. As a result, micro geometry of liner surface needs to be obtained through white light interferometry device or confocal equipment to conduct contact model. Based on real geometry of liner finish and the assumption that ring surface is ideally smooth, contact can be predicted by three different models which were developed by using statistical Greenwood-Williamson model, Hertzian contact and revised deterministic dry contact model by Professor A.A. Lubrecht. The predicted contact between liner finish and piston ring is then combined with hydrodynamic pressure caused by lubricant which was examined using TLOCR deterministic model by Chen. et al to get total friction resulted on the surface of liner finish. Finally, contact model is used to examine friction of different liners in an actual engine running cycle.
