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Journal Article

Visualization of the Rotary Engine Oil Transport Mechanisms

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. In order to better understand oil transport, a laser induced fluorescence technique is used to visualize oil motion on the side of the rotor during engine operation. Oil transport from both metered oil and internal oil is observed. Starting from inside, oil accumulates in the rotor land during inward motion of the rotor created by its eccentric motion. Oil seals are then scraping the oil outward due to seal-housing clearance asymmetry between inward and outward motion. Cut-off seal does not provide an additional barrier to internal oil consumption. Internal oil then mixes with metered oil brought to the side of the rotor by gas leakage. Oil is finally pushed outward by centrifugal force, passes the side seals, and is thrown off in the combustion chamber.
Technical Paper

The Study of Friction between Piston Ring and Different Cylinder Liners using Floating Liner Engine - Part 1

The objective of this work was to develop an experimental system to support development and validation of a model for the lubrication of two-piece Twin-Land-Oil-Control-Rings (hereafter mentioned as TLOCR). To do so, a floating liner engine was modified by opening the head and crankcase. Additionally, only TLOCR was installed together with a piston that has 100 micron cold clearance to minimize the contribution of the skirt to total friction. Friction traces, FMEP trend, and repeatability have been examined to guarantee the reliability of the experiment results. Then, engine speed, liner temperature, ring tension, and land widths were changed in a wide range to ensure all three lubrication regimes were covered in the experiments.
Technical Paper

The Influences of Cylinder Liner Honing Patterns and Oil Control Ring Design Parameters on the Interaction between the Twinland Oil Control Ring and the Cylinder Liner in Internal Combustion Engines

This paper discusses the influences of several cylinder liner honing surface geometrical features on the interaction between the piston twin land oil control ring (TLOCR) and the cylinder liner by using the deterministic hydrodynamic model [1] and the twin land oil control ring model [2]. Additionally, the key design parameters of the TLOCR, including ring tension and land axial width are studied. The results show significant effects of three liner honing surface features beyond height distribution, including plateau wavelength, groove density and honing angle in hydrodynamic pressure generation. The study in oil control ring design parameters reveals that both ring tension and land axial width have important influences on friction and oil consumption, and their competing effects are discussed subsequently.
Technical Paper

The Contribution of Different Oil Consumption Sources to Total Oil Consumption in a Spark Ignition Engine

As a part of the effort to comply with increasingly stringent emission standards, engine manufacturers strive to minimize engine oil consumption. This requires the advancement of the understanding of the characteristics, sources, and driving mechanisms of oil consumption. This paper presents a combined theoretical and experimental approach to separate and quantify different oil consumption sources in a production spark ignition engine at different speed and load conditions. A sulfur tracer method was used to measure the dependence of oil consumption on engine operating speed and load. Liquid oil distribution on the piston was studied using a Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder parameters for oil transport and oil consumption, such as liner temperatures and land pressures, were measured.
Technical Paper

Study of the Effects of Oil Supply and Piston Skirt Profile on Lubrication Performance in Power Cylinder Systems

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.
Technical Paper

Oil Transport in the Piston Ring Pack (Part II): Zone Analysis and Macro Oil Transport Model

Engine oil consumption is one of the primary interests for the automotive industry in controlling emissions and reducing service cost. Due to a lack of understanding of the mechanisms and flow patterns of oil transport along the piston, reducing oil consumption from the ring pack of internal combustion engines has been extremely challenging for engine manufacturers and suppliers. In work prior to this study (see Part I [1]), individual oil transport processes such as oil flows on the piston lands in both axial and circumferential directions, oil flows through the ring grooves and gaps and oil flows between the piston and the liner have been identified and characterized. One of the major difficulties remaining for oil transport analysis was the lack of description of how the oil transport mechanisms previously investigated affect, through the multitude of flow paths, the oil balance in the various sub-regions and the net oil flow toward the combustion chamber.
Technical Paper

Oil Transport in the Piston Ring Pack (Part I): Identification and Characterization of the Main Oil Transport Routes and Mechanisms

Engine oil consumption is one of the primary interests for the automotive industry in controlling emissions and reducing service cost. Due to a lack of understanding of the mechanisms of oil transport along the piston, reducing oil consumption from the ring pack of internal combustion engines has been extremely challenging for engine manufacturers and suppliers. Consequently, a thorough experimental characterization of oil transport processes is critical to 1) reduce lead-time and cost of new piston ring pack development, 2) provide the physically based oil transport models needed to develop analytical tools for oil consumption prediction. In this work, a two-dimensional multiple-dye Laser-Induced Fluorescence (LIF) visualization system was successfully implemented in a diesel and a spark-ignition engine.
Technical Paper

Oil Transport Phenomena during extreme load transients inside the power cylinder unit as investigated by HS-2DLIF (High-Speed 2D Laser-Induced Fluorescence)

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.
Technical Paper

Oil Transport Inside the Power Cylinder During Transient Load Changes

This paper presents a study of lubricating oil transport and exchange in a four-stroke spark ignition engine while undergoing transient load changes. The study consisted of experiments with a single cylinder test engine utilizing 2D LIF (Two Dimensional Laser Induced Fluorescence) techniques to view real time oil transport and exchange, along with computer modeling to describe certain phenomenon observed during the experiments. The computer modeling results included ring dynamics and corresponding gas flows through different regions of the power cylinder. Under steady-state conditions and constant speed during the experiments, more oil was observed on the piston at low load than at high load. Therefore, a transition from low load to high load resulted in oil leaving the piston, and a transition from high load to low load resulted in oil being added to the piston.
Journal Article

Oil Transport Cycle Model for Rotary Engine Oil Seals

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. A model of the oil seals is developed to calculate internal oil consumption (oil leakage from the crankcase through the oil seals) as a function of engine geometry and operating conditions. The deformation of the oil seals trying to conform to housing distortion is calculated to balance spring force, O-ring and groove friction, and asperity contact and hydrodynamic pressure at the interface. A control volume approach is used to track the oil over a cycle on the seals, the rotor and the housing as the seals are moving following the eccentric rotation of the rotor. The dominant cause of internal oil consumption is the non-conformability of the oil seals to the housing distortion generating net outward scraping, particularly next to the intake and exhaust port where the housing distortion valleys are deep and narrow.
Technical Paper

Modeling the Evolution of Fuel and Lubricant Interactions on the Liner in Internal Combustion Engines

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.
Technical Paper

Modeling the Dynamics and Lubrication of Three Piece Oil Control Rings in Internal Combustion Engines

The oil control ring is the most critical component for oil consumption and friction from the piston system in internal combustion engines. Three-piece oil control rings are widely used in Spark Ignition (SI) engines. However, the dynamics and lubrication of three piece oil control rings have not been thoroughly studied from the theoretical point of view. In this work, a model was developed to predict side sealing, bore sealing, friction, and asperity contact between rails and groove as well as between rails and the liner in a Three Piece Oil Control Ring (TPOCR). The model couples the axial and twist dynamics of the two rails of TPOCR and the lubrication between two rails and the cylinder bore. Detailed rail/groove and rail/liner interactions were considered. The pressure distribution from oil squeezing and asperity contact between the flanks of the rails and the groove were both considered for rail/groove interaction.
Technical Paper

Modeling of the Rotary Engine Apex Seal Lubrication

The Wankel rotary engine is more compact than conventional piston engines, but its oil and fuel consumption must be reduced to satisfy emission standards and customer expectations. A key step toward this goal is to develop a better understanding of the apex seal lubrication to reduce oil injection while reducing friction and maintaining adequate wear. This paper presents an apex seal dynamics model capable of estimating relative wear and predicting friction, by modeling the gas and oil flows at the seal interfaces with the rotor housing and groove flanks. Model predictions show that a thin oil film can reduce wear and friction, but to a limited extent as the apex seal running face profile is sharp due to the engine kinematics.
Journal Article

Modeling of Oil Transport between Piston Skirt and Cylinder Liner in Internal Combustion Engines

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.
Technical Paper

Modeling and Optimizing Honing Texture for Reduced Friction in Internal Combustion Engines

Frictional losses in the piston ring-pack of an engine account for approximately half of the total frictional losses within the power cylinder of an engine. Three-dimensional honing groove texture was modeled, and its effect on piston ring-pack friction and engine brake thermal efficiency was investigated. Adverse effects on engine oil consumption and durability were also considered. Although many non-conventional cylinder liner finishes are now being developed to reduce friction and oil consumption, the effects of surface finish on ring-pack performance is not well understood. A rough surface flow simulation program was developed to calculate flow and stress factors that adjust the solution of the Reynolds equation for the effects of surface roughness as has been done in the literature. Rough surface contact between the ring and liner was modeled using a previously published methodology for asperity contact pressure estimation between rough surfaces.
Technical Paper

Modeling Piston Ring-Pack Lubrication With Consideration of Ring Structural Response

The lubrication of the piston ring-pack is directly related to the engine friction and oil consumption. Non-axisymmetric characteristics of the power cylinder system, most noticeably cylinder bore distortion, piston secondary motion, and ring gaps, can introduce circumferential variations to ring/liner lubrication and overall performance of the ring-pack in friction and oil consumption. In order to be able to optimize the piston ring-pack in a more fundamental way, it is necessary to develop physical understanding of the effects of these non-axisymmetric properties and effective numerical tools. In this study, a comprehensive model has been developed for the lubrication of a piston ring-pack. By employing a finite element analysis, this model is capable of evaluating the in-plane structural response of a ring to external forces. A newly developed one-dimensional hydrodynamic lubrication sub-model is implemented to calculate the lubrication force at each cross-section.
Technical Paper

Modeling Engine Oil Vaporization and Transport of the Oil Vapor in the Piston Ring Pack of Internal Combustion Engines

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 a number of distinct paraffin hydrocarbons, a set of equations governing the oil vapor density variations were derived by applying 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. The results showed that, under this condition, the oil consumption from piston vaporization alone was far greater than the typical oil consumption value measured in the engine.
Technical Paper

Investigation of Oil Transport Mechanisms in the Piston Ring Pack of a Single Cylinder Diesel Engine, Using Two Dimensional Laser Induced Fluorescence

A two-dimensional Laser Induced Fluorescence (LIF) system was developed to visualize the oil distribution and study the oil transport in the piston ring pack of a single-cylinder diesel engine through an optical window on the liner. The system gives high spatial and intensity resolutions so that detailed oil distribution on the piston as well as between the rings and the liner can be studied. This work primarily focused on investigating different oil transport mechanisms on piston crown land and second land under various engine operating conditions. Oil accumulation on the crown land was observed under certain operating conditions and top ring up-scraping was deemed to be the source for this oil accumulation. Two mechanisms for the oil flow on the second land were identified, namely, inertia driven oil flow in the axial direction and oil dragging by gas flow in the circumferential direction. Finally, the effects of ring rotation were investigated.
Technical Paper

Introducing a New Piston Skirt Profile to Reduce Engine Friction

The piston’s skirt shape is a key design parameter since it critically influences lateral displacement, tilting movement, oil transport and consequently engine performances. This study proposes an alternative skirt profile that aims to reduce frictional losses between the piston and cylinder liner. Qualitatively, the proposed profile, aims to reduce solid-to-solid contact friction by increasing the total hydrodynamic forces generated on the skirt to balance side forces, and to prevent both sides of the skirt to interact with the liner simultaneously. The new skirt’s profile has been first studied and optimized using a piston secondary motion model and then prototyped and tested on a floating liner test bench, showing a 12% average reduction in total piston FMEP.
Technical Paper

Effects of Piston-Ring Dynamics on Ring/Groove Wear and Oil Consumption in a Diesel Engine

The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.