198 research outputs found

    The Impact of Micro-Surface Shaping of the Piston on the Piston/Cylinder Interface of an Axial Piston Machine

    Get PDF
    Axial piston machines of the swashplate type are commonly used in various hydraulic systems and with recent developments in displacement control, it is essential to maximize their efficiency further reducing operation costs as well as improving performance and reliability. This paper reports findings of a research study conducted for the piston-cylinder interface utilizing a novel fluid structure thermal interaction model considering solid body deformation due to thermal and pressure effects in order to accurately predict the transient fluid film within the gap. A large reduction in energy dissipation is possible due to reduced clearances allowable due to the surface shaping of the piston resulting in a reduction in leakage. From this study, it is shown that surface shaping of the piston in combination with a reduced clearance is not only beneficial by improving the efficiency of a machine, but also increases the reliability and the performance of the machine as the load support is enhanced

    A review of high-speed electro-hydrostatic actuator pumps in aerospace applications: challenges and solutions

    Get PDF
    The continued development of electro-hydrostatic actuators (EHAs) in aerospace applications has put forward an increasing demand upon EHA pumps for their high power density. Besides raising the delivery pressure, increasing the rotational speed is another effective way to achieve high power density of the pump, especially when the delivery pressure is limited by the strength of materials. However, high-speed operating conditions can lead to several challenges to the pump design. This paper reviews the current challenges including the cavitation, flow and pressure ripples, tilting motion of rotating group and heat problem, associated with a high-speed rotation. In addition, potential solutions to the challenges are summarized, and their advantages and limitations are analyzed in detail. Finally, future research trends in EHA pumps are suggested. It is hoped that this review can provide a full understanding of the speed limitations for EHA pumps and offer possible solutions to overcome them

    An Investigation of Micro-Surface Shaping on the Piston/Cylinder Interface of Axial Piston Machines

    Get PDF
    Presently, axial piston machines of the swash plate type are commonly used in industry due to their many benefits. However, with recent technological advancements in hydraulic hybrid powertrains and displacement-controlled actuation, the application of such machines has been broadened demanding a more cost-effective reliable and efficient, yet versatile machine. The fluid film geometry of the lubricating interfaces is a very complex and sensitive phenomena that must simultaneously fulfill a competing bearing and sealing function. Therefore, the design process of such machines is a difficult process while tightly constrained manufacturing tolerances are essential thereby increasing the initial production costs. Accordingly, virtual prototyping through analytical simulation in this field has emerged as an ideal tool not only to improve the performance of existing units, but to also design new and innovative axial piston machines that fulfill the demands of advanced technology. The aim of this dissertation is to investigate more efficient and reliable designs of the piston/cylinder interface of an axial piston machine over a broad range of operating conditions. Primarily, an extensive simulation study was conducted in which the design of a commercially available machine was modified to accommodate piston micro-surface shaping where the relative improvements were then quantified in comparison. This study utilizes a novel fully-coupled fluid structure interaction model considering both thermal and pressure deformations of the solid bodies to accurately predict the dynamic behavior of the lubricating interface. Having analyzed the phenomena of the lubricating gap and the effects of micro-surface shaping, an optimization technique was utilized to design this interface. The optimization scheme determines the best balance between improving the sealing function while maintaining or even improving the bearing function. A surface shaped piston was then measured and compared back to the simulation results realizing the capabilities of such a novel methodology. Ultimately, this cost-effective design process demonstrated that micro-surface shaping is beneficial as it allows for reduced clearances, achieving a reduction in volumetric losses, while increasing fluid film support, resulting in superior efficiency as well as enhanced reliability and overall performance

    Development of advanced high temperature in-cylinder components and tribological systems for low heat rejection diesel engines, phase 1

    Get PDF
    Analysis and concept design work completed in Phase 1 have identified a low heat rejection engine configuration with the potential to meet the Heavy Duty Transport Technology program specific fuel consumption goal of 152 g/kW-hr. The proposed engine configuration incorporates low heat rejection, in-cylinder components designed for operation at 24 MPa peak cylinder pressure. Water cooling is eliminated by selective oil cooling of the components. A high temperature lubricant will be required due to increased in-cylinder operating temperatures. A two-stage turbocharger air system with intercooling and aftercooling was selected to meet engine boost and BMEP requirements. A turbocompound turbine stage is incorporated for exhaust energy recovery. The concept engine cost was estimated to be 43 percent higher compared to a Caterpillar 3176 engine. The higher initial engine cost is predicted to be offset by reduced operating costs due the lower fuel consumption

    ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF TEMPERATURE-SWING INSULATION ON ENGINE PERFORMANCE

    Full text link
    In-cylinder thermal barrier materials have been thoroughly investigated for their potential improvements in thermal efficiency in reciprocating internal combustion engines. These materials show improvements both directly in indicated work and indirectly through reduced demand on the cooling system. Many experimental and analytical sources have shown reductions in heat losses to the combustion chamber walls, but converting the additional thermal energy to indicated work has proven more difficult. Gains in indicated work over the expansion stroke could be made, but these were negated by increased compression work and reduced volumetric efficiency due to charge heating. Typically, the only improvements in brake work would come from the pumping loop in turbocharged engines, or from additional exhaust energy extraction through turbine-compounding devices. The concept of inter-cycle wall-temperature-swing holds promise to reap the benefits of insulation during combustion and expansion, while not suffering the penalties incurred with hotter walls during intake and compression. The combination of low volumetric heat capacity and low thermal conductivity would allow the combustion chamber surface temperature to quickly respond to the gas temperature throughout combustion. Surface temperatures are capable of rising in response to the spike in heat flux, thereby minimizing the temperature difference between the gas and wall early in the expansion stroke when the greatest conversion of thermal energy to mechanical work is possible. The combination of low heat capacity and thermal conductivity is essential in allowing this temperature increase during combustion, and in enabling the surface to cool during expansion and exhaust to avoid harmfully affecting engine volumetric efficiency during the intake stroke and minimizing compression work performed on the next stroke. In this thesis, thermal and thermodynamic models are constructed in an attempt to predict the effects of material properties in the walls, and to characterize the effects of heat transfer at different portions of the cycle on indicated work, volumetric efficiency, exhaust energy and gas temperatures of a reciprocating internal combustion engine. The expected impact on combustion knock in spark-ignited engines was also considered, as this combustion mode was the basis for the experimental engine testing performed. Conventional insulating materials were evaluated to benchmark the current state-of-the-art, and to gain experience in the analysis of materials with temperature-swing capability. Unfortunately, the effects of permeable porosity within the conventional coating on heat losses, fuel absorption and compression ratio tended to mask the effects of temperature swing. The individual impact of each of these loss mechanisms on engine performance was analyzed, and the experience helped to further refine the necessary traits of a successful temperature-swing material Finally, from the learnings of this analysis phase, a novel material was created and applied to the piston surface, intake valve faces, and exhaust valve faces. Engine data was taken with these coated components and compared to an un-coated baseline. While some of the test pieces physically survived the testing, analysis of the data suggests that they were not fully sealed and suffered from the same permeability losses that affected the conventional insulation. Further development is necessary to arrive at a robust, effective solution for minimizing heat transfer through wall temperature swing in reciprocating internal combustion engines. The success of temperature-swing thermal barrier materials requires very low thermal conductivity, heat capacity, and appropriate insulation thickness, as well as resilient sealing of any porous volume within the coating to avoid additional heat and fuel energy losses throughout the cycle.Los materiales aislantes han sido investigados a fondo por sus posibles mejoras en la eficiencia térmica de los motores de combustión interna alternativos. Estas mejoras se ven reflejadas tanto directamente en el trabajo indicado como indirectamente a través de la reducción del sistema de refrigeración del propio motor. Diferentes estudios, tanto experimentales como analíticos, han mostrado la reducción en la transferencia de calor a través de las paredes de la cámara de combustión mediante la utilización de estos materiales. Sin embargo, demostrar la conversión de la energía térmica adicional en trabajo indicado ha resultado más difícil. En ciertos estudios se pudieron obtener mejoras en el trabajo indicado durante la carrera de expansión, pero éstas fueron reducidas debido a un menor rendimiento volumétrico debido al calentamiento de la carga durante el proceso de admisión y un mayor trabajo en la carrera de compresión. Típicamente, las únicas mejoras en el trabajo al freno provendrían de la reducción de pérdidas por bombeo en los motores turboalimentados, o de la extracción de la energía adicional de los gases de escape a través de turbinas. El concepto de los materiales con oscilación de la temperatura durante el ciclo motor intenta aprovechar los beneficios del aislamiento durante los procesos de combustión y expansión, mitigando las perdidas por el incremento de la temperatura de las paredes durante la admisión y la compresión. La combinación de baja capacidad calorífica y baja conductividad térmica permitiría que la temperatura de la superficie de la cámara de combustión respondiera rápidamente a la temperatura del gas durante el proceso de combustión. Las temperaturas de la superficie son capaces de aumentar en respuesta al pico de flujo de calor, minimizando así la diferencia de temperatura entre el gas y la pared en la carrera de expansión cuando es posible la mayor conversión de energía térmica en trabajo mecánico. La combinación de baja capacidad calorífica y conductividad térmica es también esencial para permitir este aumento de temperatura durante la combustión y para permitir que la superficie se enfríe durante la expansión y el escape para no perjudicar así el rendimiento volumétrico del motor durante la carrera de admisión y minimizar el trabajo de compresión realizado en el siguiente ciclo. En esta tesis se han desarrollado modelos térmicos y termodinámicos para predecir los efectos de las propiedades de los materiales en las paredes y caracterizar los efectos de la transferencia de calor en diferentes partes del ciclo sobre el trabajo indicado, el rendimiento volumétrico, la energía en los gases de escape y las temperaturas del gas para un motor de combustión interna alternativo. También se ha evaluado el impacto del uso de estos materiales en el knock en motores de combustión de encendido provocado, ya que los estudios experimentales de esta tesis se realizaron en un motor de estas características. Durante la investigación se evaluaron materiales aislantes convencionales para comprender el estado actual de esta técnica y para adquirir también experiencia en el análisis de materiales aislantes con oscilación de temperatura. Desafortunadamente, los efectos de la permeabilidad a través de la porosidad del material en los recubrimientos convencionales, la absorción de combustible y la relación de compresión tendieron a ocultar los efectos de la oscilación de la temperatura y la reducción de la transferencia de calor a través de las paredes. Así pues, se analizó el impacto individual de cada uno de estos mecanismos y su influencia en el rendimiento del motor para así definir un nuevo material con las características necesarias que mejorasen el aislante con de oscilación de temperatura. Finalmente, a partir de los estudios de esta fase de análisis, se creó un nuevo material y se aplicó a la superficie del pistón y a la supeEls materials aïllants han estat investigats a fons per les seves possibles millores en l'eficiència tèrmica en el motors de combustió interna alternatius. Aquestes millores es veuen reflectides tant directament en el treball indicat com indirectament a través de la reducció del sistema de refrigeració del propi motor. Diferents estudis, tant experimentals com analítics, han mostrat la reducció en la transferència de calor a través de les parets de la cambra de combustió mitjançant la utilització d'aquests materials. No obstant això, demostrar la conversió de l'energia tèrmica addicional en treball indicat ha resultat més difícil. En certs estudis es van poder obtenir millores en el treball indicat durant la carrera d'expansió, però aquestes van ser reduïdes a causa d'un menor rendiment volumètric causat de l'escalfament de la càrrega durant el procés d'admissió i un major treball en la carrera de compressió. Típicament, les úniques millores en el treball al fre provindrien de la reducció de pèrdues per bombeig en els motors turbo alimentats, o de l'extracció addicional de l'energia dels gasos d'escapament a través de turbines. El concepte dels materials amb oscil·lació de la temperatura durant el cicle motor intenta aprofitar els beneficis de l'aïllament durant els processos de combustió i expansió, mitigant les perdudes per l'increment de la temperatura de les parets durant l'admissió i la compressió. La combinació de baixa capacitat calorífica i baixa conductivitat tèrmica permetria que la temperatura de la superfície de la cambra de combustió respongués ràpidament a la temperatura del gas durant el procés de combustió. Les temperatures de la superfície són capaços d'augmentar en resposta al flux de calor, minimitzant així la diferència de temperatura entre el gas i la paret en la carrera d'expansió quan és possible la major conversió d'energia tèrmica en treball mecànic. La combinació de baixa capacitat calorífica i conductivitat tèrmica és també essencial per permetre aquest augment de temperatura durant la combustió i el refredament de la superfície durant l'expansió i l'escapament per no perjudicar així el rendiment volumètric del motor durant la carrera d'admissió i minimitzar el treball de compressió realitzat en el següent cicle. En aquesta tesi s'han desenvolupat models tèrmics i termodinàmics per predir els efectes de les propietats dels materials en les parets i caracteritzar els efectes de la transferència de calor en diferents parts del cicle sobre el treball indicat, el rendiment volumètric, l'energia en els gasos d'escapament i les temperatures del gas per un motor de combustió interna alternatiu. També s'ha avaluat l'impacte d'aquests materials en el knock en motors de combustió d'encesa provocada, ja que les proves experimentals d'aquesta tesi es van realitzar en un motor d'aquestes característiques. Durant la investigació es van avaluar materials aïllants convencionals per comprendre l'estat actual d'aquesta tècnica i per adquirir també experiència en l'anàlisi de materials aïllants amb oscil·lació de temperatura. Desafortunadament, els efectes de la permeabilitat a través de la porositat del material en el recobriment convencional, l'absorció de combustible i la relació de compressió van tendir a ocultar els efectes de l'oscil·lació de la temperatura i la reducció de la transferència de calor a través de les parets. Així doncs, es va analitzar l'impacte individual de cada un d'aquests mecanismes i la seva influència en el rendiment del motor per així definir un nou material amb les característiques necessàries que milloressin el aïllant d'oscil·lació de temperatura. Finalment, a partir dels estudis d'aquesta fase d'anàlisi, es va crear un nou material i es va aplicar a la superfície del pistó i a la superfície interna de les vàlvules d'admissió i d'escapament. Les dades de motor es van prendre aAndruskiewicz, PP. (2017). ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF TEMPERATURE-SWING INSULATION ON ENGINE PERFORMANCE [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90467TESI

    Volume 2 – Conference: Wednesday, March 9

    Get PDF
    10. Internationales Fluidtechnisches Kolloquium:Group 1 | 2: Novel System Structures Group 3 | 5: Pumps Group 4: Thermal Behaviour Group 6: Industrial Hydraulic

    Numerical modeling of piston secondary motion and skirt lubrication in internal combustion engines

    Get PDF
    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 239-241).Internal combustion engines dominate transportation of people and goods, contributing significantly to air pollution, and requiring large amounts of fossil fuels. With increasing public concern about the environment and the reliability of oil supplies, automotive companies are pushed to improve engine design in order to reduce engine emissions and fuel consumption. This project aims to develop a numerical model of piston dynamics and lubrication in internal combustion engines, enabling prediction of friction generation at the piston -cylinder bore interface, and oil transport in the power cylinder system. It is currently estimated that the piston - cylinder bore friction accounts for up to 25% of the power loss in a typical engine, while oil transported to the combustion chamber by the piston and ring-pack contributes significantly to engine emissions. A dry piston model was first developed to allow fast calculation of approximate piston dynamics. An elastohydrodynamic lubrication model was then developed to allow direct numerical simulation of the effect of piston tooling marks, and comparison with results obtained using an Average Reynolds equation with flow factors. The lubrication model was incorporated into the piston dynamics model, enabling more accurate evaluation of friction and oil transport. Comparison between the dry and lubricated model results demonstrate the effect of oil film thickness on piston lateral motion, tilt, friction generation and oil transport.by Fiona McClure.Ph.D

    Research and Technology 1995

    Get PDF
    This report selectively summarizes the NASA Lewis Research Center's research and technology accomplishments for fiscal year 1995. It comprises over 150 short articles submitted by the staff members of the technical directorates. The report is organized into six major sections: aeronautics, aerospace technology, space flight systems, engineering support, Lewis Research Academy, and technology transfer. A table of contents, an author index, and a list of NASA Headquarters program offices have been included to assist the reader in finding articles of special interest. This report is not intended to be a comprehensive summary of all research and technology work done over the past fiscal year. Most of the work is reported in Lewis-published technical reports, journal articles, and presentations prepared by Lewis staff members and contractors (for abstracts of these Lewis-authored reports, visit the Lewis Technical Report Server (LETRS) on the World Wide Web-http://letrs.lerc.nasa.gov/LeTRS/). In addition, university grants have enabled faculty members and graduate students to engage in sponsored research that is reported at technical meetings or in journal articles. For each article in this report, a Lewis contact person has been identified, and where possible, reference documents are listed so that additional information can be easily obtained. The diversity of topics attests to the breadth of research and technology being pursued and to the skill mix of the staff that makes it possible. For more information about Lewis' research, visit us on the World Wide web-http://www.lerc.nasa.gov

    Aeropropulsion 1987

    Get PDF
    Papers from the Aeropropulsion '87 Conference, held at the NASA Lewis Research Center (LeRC), are presented. Unclassified presentations by LeRC and NASA Headquarters senior management and many LeRC technical authors covered the philosophy and major directions of the LeRC aeropropulsion program, and presented a broad spectrum of recent research results in materials, structures, internal fluid mechanics, instrumentation and controls, and both subsonic and high-speed propulsion technology
    corecore