167 research outputs found
Tribology of piston compression ring conjunction under transient thermal mixed regime of lubrication
Fuel efficiency is the main IC engine attribute, with the compression ring-bore contact consuming nearly 5% of the fuel energy. Analyses are often idealised, such as isothermal condition and smooth surfaces, the former being particularly contrary to practice. An analytic solution to the average flow model is presented for this contact with a new analytical thermal model. The generated contact temperatures, particularly at the inlet result in thinner films than the idealised analyses. For the simulated city driving condition the power loss is mainly due to viscous shear under cold engine condition, whilst for a hot engine boundary friction dominates
Elastohydrodynamic Lubrication (EHL) of Piston Rings in the Internal Combustion Engine
AbstractThe paper analyzes the numerical model of elastohydrodynamic lubrication (EHL) of piston rings in the cylinder liner of the internal combustion engine (ICE). Authors take into account reactions of the lubricating layer, the pressure force of the piston rings on the cylinder wall, forces of the gas pressure in the cylinder, the friction force between the upper edge of the piston ring and the piston groove. A simulation model was developed in the Fortran program and authors have analyzed characteristics and forms of piston rings in the ICE
Tribological optimisation of the internal combustion engine piston to bore conjunction through surface modification
Internal combustion (IC) engines used in road transport applications employ pistons to convert
gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38-
51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore
conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to
1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a
direct impact on specific performance and / or fuel consumption.
In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently,
these engines have a shorter useful life and a high premium is placed on measures which
would increase the output power without further reducing engine life. Reduction of friction
offers such an opportunity, which may be achieved by improved tribological design in terms
of reduced contact area or enhanced lubrication or both. However, the developments in the
motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc
reliance, based upon a limited number of actual engine tests in order to determine if any
improvement can be achieved as the result of some predetermined action. A representative
scientific model generally does not exist and as such, investigated parameters are often driven
by the supply chain with the promise of improvement. In cylinder investigations are usually
limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the
lubricant employed. Of these investigated areas newly emerging surface coatings are arguably
seen as predominate.
This thesis highlights a scientific approach which has been developed to optimise piston-bore
performance. Pre-existing methods of screening and benchmarking alterations have been
retained such as engine testing. However, this has been placed in the context of validation of
scientifically driven development. A multi-physics numerical model is developed, which
combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic
tribological framework. Experimental tests were performed to validate
the findings of numerical models. These tests include film thickness measurement and incylinder
friction measurement, as well as the numerically-indicated beneficial surface
modifications. Experimental testing was performed on an in-house motored engine at
Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at
Loughborough University, as well as on other engines belonging to third party clients of
Capricorn. The diversity of tests was to ascertain the generic nature of any findings.
The multi-physics multi-scale combined numerical-experimental investigation is the main
contribution of this thesis to knowledge. One major finding of the thesis is the significant role
that bulk thermo-structural deformation makes on the contact conformity of piston skirt to
cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial
role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction
The influence of piston ring geometry and topography on friction
This article provides solution for isothermal mixed hydrodynamic conjunction of the compression ring to cylinder liner. This is obtained using the average flow model representation of Reynolds equation based on pressure- and shear-induced flow factors. In particular, the effects of compression ring axial profile along its face-width and surface topography of contiguous solids are investigated. It is shown that ring geometry may be optimized to improve lubrication, whilst care should be taken in order to avoid oil loss or degradation resulting from any loss of sealing. In predicting friction, it is shown that appropriate surface parameters should be used in-line with the state of wear of the ring. For a new ring against a plateau honed liner, boundary friction contribution during the initial running-in wear phase should be predicted according to the average asperity peak heights protruding above the plateau, whilst the plateau height also takes into account the valleys within the surface roughness or grooves created by any cross-hatch honing would be the appropriate measure of topography for worn rings. The main contributions of the article are in providing an analytic solution as well investigation of ring face-width geometry and effect of wear upon friction. However, it is acknowledged that generated heat, inlet boundary starvation and circumferential non-conformity of ring to the bore surface would affect the film thickness and exacerbate generated friction accordingly. These further considerations would require a numerical solution, rather than an analytical one presented here
Transient elastohydrodynamic lubrication of rough new or worn piston compression ring conjunction with an out-of-round cylinder bore
Transient elastohydrodynamic lubrication of rough new or worn piston compression ring conjunction with an out-of-round cylinder bor
Transient elastohydrodynamic analysis of piston skirt lubricated contact under combined axial, lateral and tilting motion
Most modern engines utilise pistons with an offset gudgeon pin. In internal combustion
engines, the offset is to the major thrust side of the piston. The piston thrust side is the
part of the piston perpendicular to the gudgeon pin that carries the majority of side
loading during the power stroke. Primary reason for having the gudgeon pin positioned
eccentrically is to prevent the piston from slamming into the cylinder bore after the
connecting rod journal passes the top dead centre. This phenomenon is referred to as
piston slap, and is more pronounced in compression ignition and high performance
engines due to higher combustion pressure than that of commercial spark ignition
engines. The coming together of the piston and the bore results in scuffing, at best, or,
catastrophic failure at worst. Clearance space between bore and piston is filled by a
lubricant film. The main role of the lubricant is to separate the piston and bore by
reacting to the applied load.
Investigating the above problem requires a holistic approach, whereby a dynamic three
degree-of-freedom piston model is coupled with a lubrication model to represent the
actual system. The dynamic model determines the motion of the piston in combined
axial, lateral and rotation about the gudgeon pin. The reactive forces due to lubricant
films on the major and minor thrust sides of the piston play significant roles in piston
dynamics and are evaluated by either quasi-static or transient solution of the lubricant
contact conjunctions.
The novel quasi-static analysis is carried out in the sense of its detailed approach,
including many key practical features. not incorporated in other analyses, hitherto
reported in literature. These features include first and foremost the development of a
specific contact mechanics model for evaluation of conforming contacts for piston skirt
against liner or bore. The quasi-static analysis includes many practical feature not
encountered in other literature on the subject, such as detailed surface irregularities and
modification features, and with thermal distortion. The analysis has been extended to
thermohydrodynamics, as well as micro-hydrodynamics, all with high computational
mesh densities, and robust methods of solution in space and time domains, including
effective influence Newton-Raphson method and linear acceleration integration scheme.
The transient tribo-elasto-multi-body dynamics problem includes physics of motion study
from film thickness prediction and secondary motion evaluation of the order of
micrometers and minutes of arc to large rigid body dynamics, including simultaneous
solution of the contact problem at both major and minor thrust sides. Such a
comprehensive solution has not hitherto been reported in literature.
The thesis discusses many aspects of piston dynamics problem, through the broad
spectrum of vehicle manufacture, with many pertinent practical engineering issues. In
particular, it provides solutions for high performance Formula 1 racing engines. This is
the first ever comprehensive analysis of piston tribodynamics for this range of engines at
very high combustion pressures.
This study has shown the paramount influence of profile of piston in promoting
lubrication between the contiguous bodies, as evident from the pattern of lubricant flow
through the contact. Deformation of the bodies increases the volume of lubricant in the
contact. During the reversal in direction of piston motion, when the entraining velocity
momentarily cases and reversal takes place, the load is held by an elastic squeez
Measurement and prediction of in-cylinder friction in internal combustion engines
Currently, nearly 75% of worldwide transport is powered by internal combustion engines, with the worldwide transport sector accounting for 14% of the world’s greenhouse gas emissions. With the current trend of downsizing and reducing vehicle cost, expensive solutions such as hybrids are often not viable. One solution is to reduce engine parasitic losses, thereby indirectly improving fuel efficiency, hence emissions. In terms of frictional losses, the piston-cylinder system accounts for 50% of all such losses, which altogether contribute to 20% of all engine losses. The thesis describes an efficient analytical-numerical model in terms of computation times and CPU requirements. The model is a one dimensional analytical solution of Reynolds equation using Elrods cavitation algorithm. The model also includes determination of viscous friction as well as boundary/asperity friction based on the work of Greenwood and Tripp. Lubrication rheology is adjusted for generated hydrodynamic pressures and measured conjunctional temperature based on the cylinder liner. Model predictions are supported by a range of experimental work, from basic science measurements using an instrumented precision slider bearing rig for direct measurement of friction to the development and use of a floating liner on a motored and fired high speed, high performance internal combustion engine at the real situation practical level. The thesis highlights the development of the experimental rigs/engines as well application of state of the art instrumentation and data processing. The combined numerical and experimental analysis show that a significant proportion of friction takes place at the top-dead-center reversal in the transition from the compression to the power stroke. Under motored conditions with low in-cylinder pressures this appears to follow Poiseuille friction, whereas under fired conditions with higher in-cylinder pressures causing increased compression ring sealing a mixed and/or boundary regime of lubrication is observed and predicted. Other than at the TDC reversal in both motored and fired conditions the frictional characteristics follow in direct proportion to the piston sliding velocity, therefore showing the dominance of viscous friction. One outcome of the thesis is a validated analytical model which due to its computational efficiency can now be used in industry to provide timely predictions for the compression ring contact zone. Most significantly, the thesis has established an experimental procedure, infrastructure and data processing methods which enable the determination of the regime of lubrication and the underlying mechanisms of friction generation from basic science sliding surfaces to in situ direct measurements from a fired engine at high loads and sliding speeds
Assessment and Optimization of Friction Losses and Mechanical Efficiency in Internal Combustion Engines
[ES] En la actualidad, el ambito del transporte mediante el uso de vehículo
ligero sufre un gran cambio hacia la descarbonización. Cada vez más, las
autoridades europeas restrigen las emisiones de gases de efectos invernaderos
hacia la atmósfera emitidos por estos vehículos. Soluciones alternativas a la
propulsión con energía fósil, como la implementación de vehículos eléctricos o
híbridos, no está lo suficientemente desarrollada para sustituir a los motores
de combustión interna alternativos (MCIA), debido a su todavía alto coste
de producción y baja infrastructura para abastecer la demanda de energ ́ıa
eléctrica.
En este contexto, la transición hacia una movilidad sostenible y renovable
sigue pasando por el aumento de la eficiencia y la reducción del consumo de
combustible en motores de combustión interna. Una alternativa a la mejora
de la eficiencia es la reducción de las pérdidas mecánicas por fricción, o en
otras palabras, optimización de la tribología. La tribología en un MCIA
lleva asociada aspectos mecánicos como la optimización de los acabados
superficiales de los distintos componentes que conforman el motor y la
optimización de propiedades física, químicas y reológicas del aceite que lo
compone. Esta última solución presenta un alto ratio beneficio/coste, ya que
su implementación no lleva asociada ninguna modificiación en el hardware y
su implementación es directa.
Uno de los objetivos de la Tesis Doctoral, es desarrollar un modelo 1D
que contenga la información tribológica de un motor de combustión interna
que no se puede obtener experimentalmente, que contribuya al entendimiento
y optimización de las pérdidas mecánicas por fricción y que ahorre el coste
experimental asociado a entender la tribología desde el punto de vista
empírico. Estos parámetros van desde el espesor de película de aceite entre
los componentes de un par rozante hasta la contribucción a la fricción de
las componentes hidrodinámicas y de asperezas de cada elemento rozante.
Adem ́as, se ha desarrollado un modelo cuasi estacionario para cuantificar la
energ ́ıa disipada por fricción en un ciclo de conducción real y el consumo de
combustible asociado al mismo.
As ́ı pues, a través de este modelo, se implementan soluciones que pasan
desde aceites optimizados reológicamente hasta acabados superficiales de
baja rugosidad, entendiendo la fenomenología asociada a cada tecnología
y aportando parámetros claves para la optimización de dicha solución.
Finalmente, se estima el ahorro en términos de consumo de combustible que se
puede alcanzar con estas soluciones implementadas mediante el modelo cuasi
estacionario en condiciones de conducción real[EN] Currently, the field of light-duty vehicle transport is undergoing a major shift towards decarbonisation. Increasingly, European authorities are restricting emissions of greenhouse gases into the atmosphere from these vehicles. Alternative solutions to fossil fuel propulsion, such as the implementation of electric or hybrid vehicles, are not sufficiently developed to replace internal combustion engine alternatives (ICEs), due to their still high production cost and low infrastructure to meet the demand for electric power.
In this context, the transition towards sustainable and renewable mobility continues to be based on increasing efficiency and reducing fuel consumption in internal combustion engines. An alternative to improving efficiency is the reduction of mechanical frictional losses, or in other words, optimisation of tribology. Tribology in an MCIA is associated with mechanical aspects such as the optimisation of the surface finishes of the different components that make up the engine and the optimisation of the physical, chemical and rheological properties of the oil that makes up the engine. This last solution presents a high benefit/cost ratio, as its implementation does not involve any hardware modification and its implementation is straightforward.
One of the objectives of the Doctoral Thesis is to develop a 1D model that contains the tribological information of an internal combustion engine that cannot be obtained experimentally, which contributes to the understanding and optimisation of mechanical friction losses and saves the experimental cost associated with understanding tribology from an empirical point of view. These parameters range from the oil film thickness between two tribological components to the contribution to friction of the hydrodynamic and roughness components of each friction element. In addition, a quasi-stationary model has been developed to quantify the energy dissipated by friction in a real driving cycle and the associated fuel consumption.
Thus, through this model, solutions ranging from rheologically optimised oils to low roughness surface finishes are implemented, understanding the phenomenology associated with each technology and providing key parameters for the optimisation of the solution. Finally, the savings in terms of fuel consumption that can be achieved with these solutions implemented using the quasi-stationary model in real driving conditions are estimated.[CA] Actualment, l’àmbit del transport mitjan ̧cant l’us de vehicles lleugers
pateix un gran canvi cap a la descarbonització. Cada vegada m ́es, les
autoritats europees restringeixen les emissions de gasos d’efecte hivernacle
cap a l’atmosfera emesos per aquests vehicles. Les solucions alternatives a
la propulsió amb energia fòssil, com la implementació de vehicles elèctrics o
híbrids, no està prou desenvolupada per substituir els motors de combustió
interna alternatius (MCIA), a causa del seu encara alt cost de producció i
baixa infraestructura per abastir la demanda d’energia elèctrica.
En aquest context, la transició cap a una mobilitat sostenible i renovable
continua passant per l’augment de l’eficiència i la reducció del consum de
combustible en motors de combustió interna. Una alternativa per a la millora
de l’eficiència es la reducció de les pèrdues mecàniques per fricció, o en altres
paraules, la optimització del comportament tribològic del motor. La tribologia
en un MCIA porta associada aspectes mecànics com ara l’optimització dels
acabats superficials dels diferents components que conformen el motor i
l’optimització de propietats física, químiques i reològiques de l’oli que va a
emprar. Aquesta ́ultima solució presenta una alta ratio benefici/cost, ja que
la seva implementació no porta associada cap modificació de la màquina i la
seva implementació ́es directa.
Un dels objectius de la Tesi Doctoral es desenvolupar un model 1D que
permet obtindré la informació tribològica d’un motor de combustió interna
que no es pot obtenir experimentalment, que contribueixi a l’enteniment
i l’optimització de les pèrdues mecàniques per fricció i que estalvi ̈ı el
cost experimental associat a entendre la tribologia des del punt de vista
empíric. Aquests paràmetres van des de l’espessor de pel·lícula d’oli entre
els components d’un parell tribològic fins a la contribució a la fricció dels
components amb regim hidrodinàmic i de la rugositat de cada element. A
més, s’ha desenvolupat un model gairebé estacionari per quantificar l’energia
dissipada per fricció en un cicle de conducció real i el consum de combustible
associat.
Així, a traves d’aquest model, s’implementen solucions que passen
des d’olis optimitzats reològicament fins a acabats superficials de baixa
rugositat, entenent la fenomenologia associada a cada tecnologia i aportant
paràmetres clau per optimitzar aquesta solució. Finalment, s’estima l’estalvi
en termes de consum de combustible que es pot assolir amb aquestes
solucions implementades mitjan ̧cant el model quasi estacionari en condicions
de conducció real.Agradezco al programa de Formación de Profesorado
Universitario del Ministerio de Ciencia, Innovación y Universidades por
soportar financieramiente mis estudios doctorales (FPU18/02116) y la estancia
de investigación que contribuyó a aumentar los conocimientos desarrollados en
la presente tesis doctoral (EST21/00451).Jiménez Reyes, AJ. (2022). Assessment and Optimization of Friction Losses and Mechanical Efficiency in Internal Combustion Engines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18898
Thermo-mixed hydrodynamics of piston compression ring conjunction
A new method, comprising Navier-Stokes equations, Rayleigh-Plesset volume fraction equation, an analytical control-volume thermal mixed approach and asperity interactions is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring-cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors
A multi-physics, multi-scale investigation of the piston ring pack
It is essential for the automotive industry to improve efficiency and mitigate frictional losses in IC engines. About 20-25% of these frictional losses arise as a result of the piston ring pack-liner assembly. By reducing the friction, there is potential to improve fuel consumption and emissions. This paper conducts a multi-physics, multi-scale investigation for the piston ring to cylinder liner conjunction, analysing the fundamental tribology, asperity interactions and boundary conditions. A 2D hydrodynamic model has been created based on Reynolds equation for a piston ring – cylinder liner conjunction. The model uses a finite difference method, calculating friction and the minimum film thickness over a 4-stroke engine cycle
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