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A Computational Study of the Lubricant Transport into Oil Control Ring Groove

Sloan Automotive Laboratory, Massachusetts Institute of Tech-Tianshi Fang, Zhen Meng, Sebastian Ahling, Tian Tian
  • Technical Paper
  • 2019-01-2362
Published 2019-12-19 by SAE International in United States
Lubricant transport into an oil control ring (OCR) groove through the clearance between the lower flank of the OCR and the groove was studied. A primary driving force of such lubricant transport is a dynamic pressure on the outer end of the clearance. The magnitude of the pressure depends on the flow pattern in the skirt chamfer region. Computational Fluid Dynamics (CFD) was employed to simulate the multiphase flow involving lubricant and gas in a skirt chamfer region. A correlation to predict the dynamic pressure was proposed and validated. The amount of lubricant transport into an OCR groove was found remarkable in a high-speed full-load condition.
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Study of the Effects of Oil Supply and Piston Skirt Profile on Lubrication Performance in Power Cylinder Systems

Massachusetts Institute of Technology-Zhen Meng, Sebastian Ahling, Tian Tian
  • Technical Paper
  • 2019-01-2364
Published 2019-12-19 by SAE International in United States
In internal combustion engines, the majority of the friction loss associated with the piston takes place on the thrust side in early expansion stroke. Research has shown that the Friction Mean Effective Pressure (FMEP) of the engine can be reduced if proper modifications to the piston skirt, which is traditionally barrel-shaped, are made. In this research, an existing model was applied for the first time to study the effects of different oil supply strategies for the piston assembly. The model is capable of tracking lubricating oil with the consideration of oil film separation from full film to partial film. It is then used to analyze how the optimized piston skirt profile investigated in a previous study reduces friction. It was found that the profile is able to maintain a larger amount of lubricant between the lower part of the piston skirt and the cylinder liner during compression stroke, thereby generating more hydrodynamic pressure, instead of asperity contact pressure, to balance the lateral force from piston pin.
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Oil Transport Phenomena during extreme load transients inside the power cylinder unit as investigated by HS-2DLIF (High-Speed 2D Laser-Induced Fluorescence)

Sloan Automotive Laboratory, Massachusetts Institute of Tech-Sebastian Ahling, Tian Tian
  • Technical Paper
  • 2019-01-2363
Published 2019-12-19 by SAE International in United States
This paper presents findings of optical investigations conducted via the HS-2DLIF (high-speed two-dimensional laser-induced fluorescence) technique under extreme transient conditions. These extreme conditions are a transition from WOT to closed throttle and vice versa. The goal is to gain a better understanding of oil transport magnitudes and timescales for transitions to and from extreme throttled conditions. These conditions are similar to the boundary conditions found during cylinder deactivation.The transients were conducted under motored conditions with injection and spark disabled in a speed range from 650 rpm to 3000 rpm. The load was transitioned from WOT to different low load conditions (closed, 150 mbar and 200 mbar), held at that low load for a variety of durations (10 sec - 600 sec), before going back to WOT. The experiments showed a strong dependence of oil transport on speed and load. The higher the speed, the faster the oil transport.When transitioning to WOT in cases with a lot of oil in the ring pack, a drastic blow-by increase could be measured. The cause of the phenomena could…
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Modeling of Oil Transport between Piston Skirt and Cylinder Liner in Internal Combustion Engines

SAE International Journal of Advances and Current Practices in Mobility

Massachusetts Institute of Technology-Zhen Meng, Sebastian Ahling, Tian Tian
  • Journal Article
  • 2019-01-0590
Published 2019-04-02 by SAE International in United States
The distribution of lubricating oil plays a critical role in determining the friction between piston skirt and cylinder liner, which is one of the major contributors to the total friction loss in internal combustion engines. In this work, based upon the experimental observation an existing model for the piston secondary motion and skirt lubrication was improved with a physics-based model describing the oil film separation from full film to partial film. Then the model was applied to a modern turbo-charged SI engine. The piston-skirt FMEP predicted by the model decreased with larger installation clearance, which was also observed from the measurements using IMEP method at the rated. It was found that the main period of the cycle exhibiting friction reduction is in the expansion stroke when the skirt only contacts the thrust side for all tested installation clearances. The main reason for lower skirt friction with larger clearance is greater amount of oil available during the expansion stroke.
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Reliable Processes of Simulating Liner Roughness and Its Lubrication Properties

Massachusetts Institute of Technology-Renze Wang, Chongjie Gu, Tian Tian
Published 2019-04-02 by SAE International in United States
Topology of liner finish is critical to the performance of internal combustion engines. Proper liner finish simulation processes lead to efficient engine design and research. Fourier methods have been well studied to numerically generate liner topology. However, three major issues wait to be addressed to make the generation processes feasible and reliable. First, in order to simulate real plateau honed liners, approaches should be developed to calculate accurate liner geometric parameters. These parameters are served as the input of the generation algorithm. Material ratio curve, the common geometry calculation method, should be modified so that accurate root mean square of plateau height distribution could be obtained. Second, the set of geometric parameters used in generating liner finish (ISO 13565-2) is different from the set of parameters used in manufacturing industry (ISO 13565-3). Quantitative relations between these two sets should be studied. Third, numerically generated liners should be run in deterministic lubrication, dry contact, and engine cycle models. Their outcome behavior should be compared with experimental data. In this article, efforts were made to fill all…
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Modeling the Evolution of Fuel and Lubricant Interactions on the Liner in Internal Combustion Engines

Massachusetts Institute of Technology-Qin Zhang, Vinayak Teja Kalva, Tian Tian
Published 2018-04-03 by SAE International in United States
In internal combustion engines, a portion of liquid fuel spray may directly land on the liner and mix with oil (lubricant), forming a fuel-oil film (~10μm) that is much thicker than the original oil film (~0.1μm). When the piston retracts in the compression stroke, the fuel-oil mixture may have not been fully vaporized and can be scraped by the top ring into the 1st land crevice and eventually enter the combustion chamber in the format of droplets. Studies have shown that this mechanism is possibly a leading cause for low-speed pre-ignition (LSPI) as the droplets contain oil that has a much lower self-ignition temperature than pure fuel. In this interest, this work aims to study the oil-fuel interactions on the liner during an engine cycle, addressing molecular diffusion (in the liquid film) and vaporization (at the liquid-gas interface) to quantify the amount of fuel and oil that are subject to scraping by the top ring, thereby exploring their implications on LSPI and friction. An analytical model is developed by coupling multi-component heat and mass transfer…
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Curved Beam Based Model for Piston-Ring Designs in Internal Combustion Engines: Working Engine Conditions Study

Massachusetts Institute of Technology-Mohamed Aziz Bhouri, Tian Tian
Published 2018-04-03 by SAE International in United States
A new multi-scale curved beam based model was developed for piston-ring designs. This tool is able to characterize the behavior of a ring with any cross section design. This paper describes the conformability and ring static twist calculation. The conformability part model the static behavior of the ring in working engine conditions. The model employs the computation scheme that separates the meshing of the structure and local force generation. Additional to the conventional static ring-bore conformability analysis, the conformability model is designed to examine ring-bore and ring-groove interactions in a running engine under varying driving forces and localized lubrication conditions. We made Improvements on the way to handle the effects of the radial temperature gradient compared to the existing models. Examples are given on the effects of ring rotation on the interaction of the ring and a distorted bore as well as the change of local lubrication conditions. Ring static twist calculation was also included to provide necessary input for 2D models. The present model can become a viable ring design tool revealing not only…
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Curved Beam Based Model for Piston-Ring Designs in Internal Combustion Engines: Closed Shape Within a Flexible Band, Free-Shape and Force in Circular Bore Study

Massachusetts Institute of Technology-Mohamed Aziz Bhouri, Tian Tian
Published 2018-04-03 by SAE International in United States
A new multi-scale curved beam based model was developed for piston-ring designs. This paper describes the free-shape, force in circular bore and closed shape within a flexible band (ovality) related parts. Knowing any one of these distributions, this model determines the other two. This tool is useful in the sense that the characterization of the ring is carried out by measuring its closed shape within a flexible band which is more accurate than measuring its free shape or force distribution in circular bore. Thus, having a model that takes the closed shape within a flexible band as an input is more convenient and useful based on the experiments carried out to characterize the ring.
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A One-Line Correlation for Predicting Oil Vaporization from Liner for IC Engines

MTU Friedrichshafen GmbH-Philipp Koeser
Massachusetts Institute of Technology-Qin Zhang, Tian Tian
Published 2018-04-03 by SAE International in United States
The increasingly stringent regulations for fuel economy and emissions require better optimization and control of oil consumption. One of the primary mechanisms of oil consumption is vaporization from the liner; we consider this as the “minimum oil consumption (MOC).” This paper presents a physical-mathematical cycle model for predicting the MOC. The numerical simulations suggest that the MOC is markedly sensitive to oil volatility, liner temperature, engine load and speed but less sensitive to oil film thickness. A one-line correlation is proposed for quick MOC estimations. It is shown to have <15% error compared to the cycle MOC computation.In the “dry region” (between top ring and OCR at the TDC), oil is depleted due to high heat and continual exposure to the combustion chamber. MTU Friedrichshafen GmbH, who develops and produces large high-speed engines and propulsion systems, conducted experiments on an single-cylinder diesel engine, which is only used for test purposes and measured the oil content in the exhaust gas via radioactive markers. This measured oil consumption was a result of both oil transport and oil vaporization.…
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Development and Application of Ring-Pack Model Integrating Global and Local Processes. Part 1: Gas Pressure and Dynamic Behavior of Piston Ring Pack

SAE International Journal of Engines

Massachusettes Institute of Technology-Yang Liu
Massachusetts Institute of Technology-Tian Tian
  • Journal Article
  • 2017-01-1043
Published 2017-03-28 by SAE International in United States
A new ring pack model has been developed based on the curved beam finite element method. This paper describes the first part of this model: simulating gas pressure in different regions above piston skirt and ring dynamic behavior of two compression rings and a twin-land oil control ring. The model allows separate grid divisions to resolve ring structure dynamics, local force/pressure generation, and gas pressure distribution. Doing so enables the model to capture both global and local processes at their proper length scales. The effects of bore distortion, piston secondary motion, and groove distortion are considered. Gas flows, gas pressure distribution in the ring pack, and ring structural dynamics are coupled with ring-groove and ring-liner interactions, and an implicit scheme is employed to ensure numerical stability. The model is applied to a passenger car engine to demonstrate its ability to predict global and local effects on ring dynamics and oil transport.
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