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Viewing 1 to 23 of 23
1990-02-01
Technical Paper
900683
Thomas Morel, Rifat Keribar
The warmup characteristics of an engine have an important impact on a variety of design issues such as performance, emissions and durability. A computer simulation has been developed which permits a detailed transient simulation of the engine warmup period from initial ambient conditions to a fully warmed up state. The simulation combines a detailed crankangle-by-crankangle calculation of in-cylinder processes and of engine air flow, with finite element heat conduction calculations of heat transfer from the gases, through the structure to the coolant. The paper describes one particular application of the simulation to the warmup of a 2.5ℓ spark ignited engine from cold start to a fully warmed up state at several speeds ranging from 1600 to 5200 rpm and loads ranging from 25% to 100% at each speed. The response of structure temperatures, charge temperature at IVC and of the exhaust temperature has been calculated and is documented in terms of characteristic warmup times.
1986-03-01
Technical Paper
860316
Thomas Morel, Rifat Keribar, Paul N. Blumberg, Edward F. Fort
A comprehensive diesel engine system model, representing in detail engine heat transfer processes, has been applied to a study of insulated diesel engines. The study involved a broad design analysis matrix covering a range of engine configurations with and without inter-cooling and exhaust heat recovery devices, three operating conditions and seven heat rejection packages. The main findig of this study is that the retained heat conversion efficiency (RHCE), of the in-cylinder heat retained by insulation to piston work, is 35-40 percent; these levels of RHCE are larger than those predicted by previous models. This means that a significant part of the retained heat is converted directly to piston work rather than being merely available in the exhaust stream, from which it would be recoverable with a much lower efficiency.
1986-03-01
Technical Paper
860445
Thomas Morel, Rifat Keribar
A new model for radiation heat transfer in DI diesel engines has been developed. The model calculates the heat transfer rates as a function of the instantaneous values of the radiation zone size, radiation temperature, and of the absorption coefficient of the soot-laden gas. The soot concentration levels are calculated from kinetic expressions for soot formation and burnup. The spatial distribution of the radiant heat flux along the combustion chamber walls is calculated by a zonal model. The model has been applied to a conventional heavy duty highway DI diesel engine to generate predictions over a range of engine speeds and loads. These predictions indicated a wide variation in the ratio of radiation to the total heat transfer, ranging from less than ten percent to more than thirty percent, depending on the speed and load.
1988-02-01
Technical Paper
880131
Thomas Morel, Rifat Keribar, Paul N. Blumberg
The development of I.C. engines is a sophisticated process bringing together a multitude of specialists. It is important that all of these specialists work together as a team and communicate effectively. One tool of communication can be an integrated engineering software package that simulates many of the important facets of engine operation, and describes their essential interactions. Then, if changes are made in one part of the hardware or in operating conditions, their effects on other components of the system can be assessed. This paper describes initial efforts made in that direction through the development of a comprehensive engine simulation code, IRIS, which permits a coupled analysis of engine performance and component thermal and structural state.
1987-02-01
Technical Paper
870162
Rifat Keribar, Thomas Morel
An integrated transient engine simulation methodology has been developed to allow the calculation of a thermal shock as it propagates in time through the engine structure. It links, in a fully consistent way, a very comprehensive thermodynamic model of in-cylinder processes, including a detailed gas-phase heat transfer representation, with a turbocharger/air flow/plenum model and a finite element model of the structure. The methodology tracks the turbocharger boost increase and the cycle-by-cycle build-up of in-cylinder heat transfer during engine load and speed changes, producing a transient thermal response in the structure, until new steady-state is reached. The presented results highlight the calculated transient engine performance response and the thermal and stress response of various metal and ceramic components during sudden speed and load changes in heavy duty diesel engines.
1985-02-25
Technical Paper
850360
Thomas Morel, Rifat Keribar, Paul N. Blumberg
The heat flux from the gases to the walls of I.C. engines is highly transient, producing temperature transients in thin layers of the walls adjacent to the combustion chamber. The resulting surface temperature swings affect engine performance, and also increase the maximum temperature of the engine components. To analyze these effects, a one-dimensional, time-dependent heat conduction model was developed, with the capability to handle layered or laminated walls and temperature-dependent material properties. The model is driven by a thermodynamic cycle code coupled to a steady-state heat conduction model of the engine structure. A parametric study was carried out in which boundary conditions representing a heavy duty diesel engine were applied to materials with a wide range of thermal properties.
1985-02-01
Technical Paper
850204
Thomas Morel, Rifat Keribar
A new model for corrective in-cylinder heat transfer has been developed which calculates heat transfer coefficients based on a description of the in-cylinder flow field. The combustion chamber volume is divided into three regions in which differential equations for angular momentum, turbulent kinetic energy and turbulent dissipation are solved. The resultant heat transfer coefficients are strongly spatially non-uniform, unlike those calculated from standard correlations, which assume spatial uniformity. When spatially averaged, the heat transfer coefficient is much more peaked near TDC of the compression stroke as compared to that predicted by standard correlations. This is due to the model's dependence on gas velocity and turbulence, both of which are amplified near TDC. The new model allows a more accurate calculation of the spatial distribution of the heat fluxes. This capability is essential for calculation of heat transfer and of component thermal loading and temperatures.
2005-04-11
Technical Paper
2005-01-1650
Jesus Rodriguez, Rifat Keribar, Greg Fialek
A model of roller chain and sprocket dynamics was developed, aimed at analyses of dynamic effects of chain drive systems in automotive valvetrains. Each chain link is modeled as a rigid body with planar motion, with three degrees of freedom and connected to adjacent links by means of a springs and dampers. The kinematics of roller-sprocket contacts are modeled in full detail. Sprocket motions in the chain's plane, resulting from torsional and bending motions of attached camshafts are also taken into account. One or two-sided guides can be treated as well as stationary, sliding or pivoting tensioners operated mechanically or hydraulically. The model also takes into account the contact kinematics between chain link rollers and guides or tensioners, allowing for guides/tensioners of arbitrary shape, or simpler (flat and circular) geometries. The model is first applied to study the chain drive and valvetrain of a 1-cylinder motorcycle engine.
2005-04-11
Technical Paper
2005-01-1649
Jesus Rodriguez, Rifat Keribar, Greg Fialek
A new model of spur gear contact and gear dynamics was developed for use in studies of dynamic response of mechanical systems involving geartrains. The model is general; in this paper it is applied to geartrain dynamics in valvetrain gear drives. The model dynamically uses a gear contact formulation based on exact involute geometries of gear teeth and can therefore account for varying, non-linear mesh stiffness. It can also account for gear torsional stiffness as well as shaft stiffness at gear centers. The paper further proposes an alternative to dynamic calculation of instantaneous gear tooth contact conditions. The proposed method uses a varying effective mesh stiffness pre-computed through static calculation of contact conditions between teeth of a gear pair, for one mesh, or tooth engagement-disengagement, period. The technique is shown to significantly reduce computational time, while closely matching the predictions of the full model.
2015-04-14
Journal Article
2015-01-0677
Marcin Marek Okarmus, Rifat Keribar, Rob Zdrodowski, Arup Gangopadhyay
Abstract Valvetrain friction can represent a substantial portion of overall engine friction, especially at low operating speed. This paper describes the methodology for predictive modeling of frictional losses in the direct-acting mechanical bucket tappet-type valvetrain. The proposed modeling technique combines advanced mathematical models based on established theories of Hertzian contact, hydrodynamic and elastohydrodynamic lubrication (EHL), asperity contact of rough surfaces, flash temperature, and lubricant rheology with detailed measurements of lubricant properties and surface finish, driven by a detailed analysis of valvetrain system kinematics and dynamics. The contributions of individual friction components to the overall valvetrain frictional loss were identified and quantified. Calculated valvetrain friction was validated against motored valvetrain friction torque measurements on two engines.
2013-04-08
Journal Article
2013-01-1118
Marcin Marek Okarmus, Rifat Keribar, Diana-Lucinia Dascalescu, Rob Zdrodowski
The helical spring is one of fundamental mechanical elements used in various industrial applications such as valves, suspension mechanisms, shock and vibration absorbers, hand levers, etc. In high speed applications, for instance in the internal combustion engine or in reciprocating compressor valves, helical springs are subjected to dynamic and impact loading, which can result in a phenomenon called “surge”. Hence, proper design and selection of helical springs should consider modeling the dynamic and impact response. In order to correctly characterize the physics of a helical spring and its response to dynamic excitations, a comprehensive model of spring elasticity for various spring coil and wire geometries, spring inertial effects as well as contacts between the windings leading to a non-linear spring force behavior is required. In practical applications, such models are utilized in parametric design and optimization studies.
2010-04-12
Technical Paper
2010-01-1058
Jesus Rodriguez, Rifat Keribar, Jielong Wang
Belt-drive systems are a commonly used for power transmission in automotive applications, notably in engine and vehicle auxiliary subsystem drives. In order to characterize the physics of a belt drive system and its response to speed and load excitations, a comprehensive model of belt elasticity and of belt-pulley contact and friction is required. In practical applications such models are utilized in parametric design and optimization studies, and computational efficiency is therefore also a key requirement. In this paper a belt drive dynamics model is presented, in which the belt is modeled by means of geometrically exact cables that can undergo large rigid body motions but whose strains remain small. The Finite Element approach is used in order to efficiently discretize these elastic components. In addition, a state-of-the-art dynamic friction model (LuGre) is used in order to model the friction loads between the belt and pulleys.
1992-02-01
Technical Paper
920484
Zafer Dursunkaya, Rifat Keribar
This paper describes a general model for the analysis of secondary motions in conventional and articulated piston assemblies. The model solves for the axial, lateral and rotational departures in positions and motions from the nominal kinematics, resulting from clearances within the piston assembly and also between the piston assembly components and the cylinder. The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Motions of the piston, pin, rod and (for articulated pistons) skirt are separately calculated, by integrating equations of motion for individual components and dynamic degrees of freedom. Various configurations with respect to rigid attachment of the wristpin to other components can also be represented. In the equations of motions solved, all gas pressure, inertia, friction and oil or contact pressure forces are accounted for.
1992-02-01
Technical Paper
920483
Rifat Keribar, Zafer Dursunkaya
This paper describes a comprehensive model of piston skirt lubrication, developed for use in conjunction with piston secondary dynamic analysis, to accurately characterize the effects of the skirt-cylinder oil film on piston motions. The model represents both hydrodynamic and boundary lubrication modes and applies an asperity contact pressure when surfaces are in close proximity with each other. In addition to skirt dimensions and surface roughness properties, the circumferential extent of lubrication, an arbitrary skirt profile and bore distortion are specifiable inputs to the model. The model is also extended to represent the oil starvation at the cylinder end of the skirt by allowing the axial extent of lubrication on the skirt surface to vary circumferentially and with time to satisfy continuity of oil.
1993-03-01
Technical Paper
930792
Zafer Dursunkaya, Rifat Keribar, Dana E. Richardson
Inter-ring gas pressures and blowby in a diesel engine were investigated analytically and compared to experimental data measured at three engine speeds. Coupled simulations of ring dynamics, ring lubrication and inter-ring gas dynamics were carried out using the RINGPAK software, a code for the integrated analysis of ring pack performance and tribology. Inter-ring pressures and ring dynamics are known to have an important effect on the “blowback” mechanism of in-cylinder oil consumption, i.e. that of oil-laden gas flow from the ring lands into the cylinder. Predicted land pressures matched the experimental results very well qualitatively as well as quantitatively. The coupling between ring motions and inter-ring gas pressures and blowby, a key feature of the methodology, was seen to be crucial in obtaining agreement with detailed features of the land pressure data.
1993-03-01
Technical Paper
930793
Rifat Keribar, Zafer Dursunkaya, Venkatesh Ganapathy
An integrated simulation methodology for the analysis of piston tribology is presented. The methodology is comprised of coupled models of piston secondary dynamics, skirt oil film elastohydrodynamic lubrication and wristpin bearing hydrodynamics, developed earlier by the authors. Models have been further expanded to calculate distributions of cumulative wear load on the skirt and cylinder and to account for details of skirt crankcase end geometry. The skirt elasticity model has also been improved to account for the effects of piston crown and pin boss stiffness in conventional, one-piece pistons. The model predicts piston assembly secondary motions, piston (skirt) friction, skirt and wristpin oil film pressures, transient deformations, skirt-cylinder contact/impact pressures and skirt and cylinder wear loads.
1992-10-01
Technical Paper
922202
Syed Wahiduzzaman, Rifat Keribar, Zafer Dursunkaya, Frank A. Kelley
A model for oil consumption due to in-cylinder evaporation of oil in reciprocating engines, has been developed. The model is based on conservation of mass and energy on the surface of the oil film left on the cylinder by a piston ring pack, at the oil/gas interface, and also conservation of energy within the oil film and cylinder/coolant interface. The model is sensitive to in-cylinder conditions and is part of an integrated model of ring pack performance, which provides the geometry of the oil film left by the ring pack on the cylinder. Preliminary simulation results indicate that a relatively small but not insignificant fraction (2-5%) of the total oil consumption may be due to evaporation losses for a heavy duty diesel at the rated condition. The evaporation rate was shown to be sensitive to oil grade and upper cylinder temperature. Much of these losses occur during the non-firing half of the cycle.
2006-04-03
Technical Paper
2006-01-0887
Marcin Okarmus, P. S. Reddy, Rifat Keribar, Richard Ham
Changing and more stringent emissions norms and fuel economy requirements often call for modifications in the fuel injection system of a Diesel engine. There exists a strong interaction between the injection system hydraulics and the dynamics of mechanical components within the unit injector and the camshaft-driven mechanical system used to pressurize it. Hence, accurate predictive analysis of design issues or evaluation of design changes requires highly coupled and integrated hydro-mechanical simulations, combining analysis of fuel injection hydraulics and the dynamics of all mechanical parts, including the cam-drive system. This paper presents an application of such an integrated model to the study and alleviation of an observed increase in mechanical vibration and related noise levels associated with a proposed design change in unit injectors and valve-train of a 6-cylinder truck diesel engine.
2008-04-14
Technical Paper
2008-01-0292
Marcin Okarmus, Rifat Keribar, Marcello Oliva, Nicola Tonin
There exists a strong interaction between the engine cylinder, intake and exhaust gas flow dynamics and the dynamics of mechanical and hydraulic components constituting the valvetrain system, which controls the engine gas flow. Technologies such as turbo-charging and Diesel particulate filtration (DPF) can significantly increase port gas pressure forces acting on the exhaust valve. When such systems are introduced or undergo design modifications, the operation of valvetrain system can be greatly affected and even compromised, which in turn may lead to degradation of performance of the internal combustion engine. Often, the valvetrain system needs to be retuned. Further, predictive analysis of design issues or evaluation of design changes requires highly coupled simulations, combining models of gas pressure forces and the dynamics of all mechanical and hydro-mechanical parts constituting the valvetrain.
2000-03-06
Technical Paper
2000-01-0562
Rifat Keribar
A multi-purpose valvetrain analysis tool has been developed, which is aimed at addressing all design issues arising in various stages of valvetrain development. Its capabilities include polynomial cam design, valvetrain mechanism kinematics, quasi-dynamic analysis, spring design/selection, multi-body elastic analysis of a single valvetrain with cam-follower and bearing tribology, and multi-valvetrain dynamics with camshaft torsional vibrations. The basic architecture of this tool is object-oriented. Its underlying basis is a library of cam design methods, kinematics operators, and dynamics/hydraulics/tribology primitives (masses, dampers, springs, etc.). On top of this basic system lies a higher-level library of valvetrain compound objects, which are pre-programmed sub-assemblies of valvetrain components built from the primitives. These high level objects minimize modeling effort and may be mixed with primitives, allowing construction of models for virtually any valvetrain.
2000-03-06
Technical Paper
2000-01-0934
Christopher Ciesla, Rifat Keribar, Thomas Morel
Engine and vehicle development is a multi-step process: from component design, to system integration, to system control. There is a multitude of tools that are currently being used in the industry for these purposes. They include detailed simulations for component design on one hand, and simplified models for system and control applications on the other hand. This introduces one basic problem: these tools are almost totally disconnected, with attendant loss of accuracy and productivity. An integrated simulation tool has been developed, which is applicable to all of the design issues enumerated above. A key feature introduced for the first time by this new tool is that it is truly a single code, with identical handling of engine and powertrain elements. Further, it contains multiple levels of engine and powertrain models, so that the user can select the appropriate level for the project at hand (e.g. depending on the time scale of the problem).
2003-03-03
Technical Paper
2003-01-0372
Thomas Morel, Rifat Keribar, Andy Leonard
An integrated simulation tool has been developed, which is applicable to a wide range of design issues. A key feature introduced for the first time by this new tool is that it is truly a single code, with identical handling of engine, powertrain, vehicle, hydraulics, electrical, thermal and control elements. Further, it contains multiple levels of engine models, so that the user can select the appropriate level for the time scale of the problem (e.g. real-time operation). One possible example of such a combined simulation is the present study of engine block vibration in the mounts. The simulation involved a fully coupled model of performance, thermodynamics and combustion, with the dynamics of the cranktrain, engine block and the driveline. It demonstrated the effect of combustion irregularity on engine shaking in the mounts.
1999-03-01
Technical Paper
1999-01-0907
Thomas Morel, Rifat Keribar, John Silvestri, Syed Wahiduzzaman
An increasing emphasis is being placed in the vehicle development process on transient operation of engines and vehicles, and of engine/vehicle integration, because of their importance to fuel economy and emissions. Simulations play a large role in this process, complementing the more usual test-oriented hardware development process. This has fueled the development and continued evolution of advanced engine and powertrain simulation tools which can be utilized for this purpose. This paper describes a new tool developed for applications to transient engine and powertrain design and optimization. It contains a detailed engine simulation, specifically focused on transient engine processes, which includes detailed models of engine breathing (with turbocharging), combustion, emissions and thermal warm-up of components. Further, it contains a powertrain and vehicle dynamic simulation.
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