Análise da influência da contaminação do lubrificante por biodiesel em um equipamento Pin-on-disk

Pós-graduação em Engenharia Mecânica - FEIS

Torneamento de liga de níquel Pyromet 31V (N07032) com ferramentas de metal duro

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

O estudo da usinagem em torneamento da superliga à base de níquel Pyromet 31v

The search for materials with higher properties and characteristics (wear resistance, oxidation, corrosion, etc.) has driven research of various materials. Among the materials that are being studied with such properties and characteristics are super alloys based on nickel which has an important role in the aeronautical, automotive, marine, production of gas turbines and now in space vehicles, rocket engineering , experimental aircraft, nuclear reactors, steam-powered plants, petrochemical and many other applications because besides having all the characteristics and properties mentioned above also have an excellent performance at high temperatures. The super alloy based on nickel studied in this work is the super alloy Pyromet 31v normally used in the manufacture of exhaust valves in common engines and diesel engines of high power by cater requirements such as mechanical strength and corrosion resistance at temperatures of approximately 815 ° C. The objective of this work is to produce results to demonstrate more specific information about the real influence of coatings on cutting tools and cutting fluids in turning and thus promote the optimization of the machining of these alloys. The super alloy Pyromet 31v was processed through turning, being performed with various machining parameters such as cutting speed, feed rate, depth in conditions of Minimum Amount of Fluid (MAF), abundant fluid, cutting tools with coating and without coating in early in his work life and with wear. After turning were obtained several samples of chips and the part generated during the machining process, was measured roughness of the material, subsequently made macrostructural analysis of the tools used order to detect possible wear and microstructural analysis of samples collected being that the latter was used for Optical Microscopy, Scanning Electron Microscopy (SEM) and ... (Complete abstract click electronic access below)

Sviluppo di algoritmi di RCP per la stima della coppia indicata erogata da un motore a combustione interna.

Combustion control is one of the key factors to obtain better performances and lower pollutant emissions for diesel, spark ignition and HCCI engines. An algorithm that allows estimating, as an example, the mean indicated torque for each cylinder, could be easily used in control strategies, in order to carry out cylinders trade-off, control the cycle to cycle variation, or detect misfires. A tool that allows evaluating the 50% of Mass Fraction Burned (MFB50), or the net Cumulative Heat Release (CHRNET), or the ROHR peak value (Rate of Heat Release), could be used to optimize spark advance or to detect knock in gasoline engines and to optimize injection pattern in diesel engines. Modern management systems are based on the control of the mean indicated torque produced by the engine: they need a real or virtual sensor in order to compare the measured value with the target one. Many studies have been performed in order to obtain an accurate and reliable over time torque estimation. The aim of this PhD activity was to develop two different algorithms: the first one is based on the instantaneous engine speed fluctuations measurement. The speed signal is picked up directly from the sensor facing the toothed wheel mounted on the engine for other control purposes. The engine speed fluctuation amplitudes depend on the combustion and on the amount of torque delivered by each cylinder. The second algorithm processes in-cylinder pressure signals in the angular domain. In this case a crankshaft encoder is not necessary, because the angular reference can be obtained using a standard sensor wheel. The results obtained with these two methodologies are compared in order to evaluate which one is suitable for on board applications, depending on the accuracy required.

Sviluppo di sistemi per l'analisi della combustione in tempo reale per motori endotermici alternativi

I moderni motori a combustione interna diventano sempre più complessi L'introduzione della normativa antinquinamento EURO VI richiederà una significativa riduzione degli inquinanti allo scarico. La maggiore criticità è rappresentata dalla riduzione degli NOx per i motori Diesel da aggiungersi a quelle già in vigore con le precedenti normative. Tipicamente la messa a punto di una nuova motorizzazione prevede una serie di test specifici al banco prova. Il numero sempre maggiore di parametri di controllo della combustione, sorti come conseguenza della maggior complessità meccanica del motore stesso, causa un aumento esponenziale delle prove da eseguire per caratterizzare l'intero sistema. L'obiettivo di questo progetto di dottorato è quello di realizzare un sistema di analisi della combustione in tempo reale in cui siano implementati diversi algoritmi non ancora presenti nelle centraline moderne. Tutto questo facendo particolare attenzione alla scelta dell'hardware su cui implementare gli algoritmi di analisi. Creando una piattaforma di Rapid Control Prototyping (RCP) che sfrutti la maggior parte dei sensori presenti in vettura di serie; che sia in grado di abbreviare i tempi e i costi della sperimentazione sui motopropulsori, riducendo la necessità di effettuare analisi a posteriori, su dati precedentemente acquisiti, a fronte di una maggior quantità di calcoli effettuati in tempo reale. La soluzione proposta garantisce l'aggiornabilità, la possibilità di mantenere al massimo livello tecnologico la piattaforma di calcolo, allontanandone l'obsolescenza e i costi di sostituzione. Questa proprietà si traduce nella necessità di mantenere la compatibilità tra hardware e software di generazioni differenti, rendendo possibile la sostituzione di quei componenti che limitano le prestazioni senza riprogettare il software.

Reduction of Transient Particulate Matter Spikes with Decision Tree Based Control

Decision trees have been proposed as a basis for modifying table based injection to reduce transient particulate spikes during the turbocharger lag period. It has been shown that decision trees can detect particulate spikes in real time. In well calibrated electronically controlled diesel engines these spikes are narrow and are encompassed by a wider NOx spike. Decision trees have been shown to pinpoint the exact location of measured opacity spikes in real time thus enabling targeted PM reduction with near zero NOx penalty. A calibrated dimensional model has been used to demonstrate the possible reduction of particulate matter with targeted injection pressure pulses. Post injection strategy optimized for near stoichiometric combustion has been shown to provide additional benefits. Empirical models have been used to calculate emission tradeoffs over the entire FTP cycle. An empirical model based transient calibration has been used to demonstrate that such targeted transient modifiers are more beneficial at lower engine-out NOx levels.

Design and Use of an Alternative Fuel Testing Apparatus and Assessment of the Feasibility of Biodiesel

Petroleum supply and environmental pollution issues constantly increase interest in renewable low polluting alternative fuels. Published test results show decreased pollution with similar power output and fuel consumption from Internal Combustion Engines (ICE) burning alternative fuels. More specifically, diesel engines burning biodiesel derived from plant oils and animal fats not only reduce harmful exhaust emissions but are renewable and environmentally friendly. To validate these claims and assess the feasibility of alternative fuels, independent engine dynamometer and emissions testing was performed. A testing apparatus capable of making relevant measurements was designed, built, and used to test and determine the feasibility of biodiesel. The apparatus marks the addition of a valuable testing tool to the University and provides a foundation for future experiments. This thesis will discuss the background of biodiesel, testing methods, design and function of the testing apparatus, experimental results, relevant calculations, and conclusions.

Parameter identification of a copper-zeolite SCR catalyst model using reactor data

The selective catalytic reduction system is a well established technology for NOx emissions control in diesel engines. A one dimensional, single channel selective catalytic reduction (SCR) model was previously developed using Oak Ridge National Laboratory (ORNL) generated reactor data for an iron-zeolite catalyst system. Calibration of this model to fit the experimental reactor data collected at ORNL for a copper-zeolite SCR catalyst is presented. Initially a test protocol was developed in order to investigate the different phenomena responsible for the SCR system response. A SCR model with two distinct types of storage sites was used. The calibration process was started with storage capacity calculations for the catalyst sample. Then the chemical kinetics occurring at each segment of the protocol was investigated. The reactions included in this model were adsorption, desorption, standard SCR, fast SCR, slow SCR, NH3 Oxidation, NO oxidation and N2O formation. The reaction rates were identified for each temperature using a time domain optimization approach. Assuming an Arrhenius form of the reaction rates, activation energies and pre-exponential parameters were fit to the reaction rates. The results indicate that the Arrhenius form is appropriate and the reaction scheme used allows the model to fit to the experimental data and also for use in real world engine studies.

Estudio técnico-económico de una planta de producción de biodiesel

Se explica las posibles razones que han obligado a varias de las plantas de biodiésel en España a cerrar a pesar de estar siendo auspiciadas por la Unión Europea y fomentadas, mediante normativas específicas y ayudas sustanciales en cada uno de los países miembros, a fin de reforzar la utilización de los biocarburantes, como energía alternativa a los combustibles fósiles, debido a las ventajas medioambientales y sociopolíticas que conllevan. Para ello se ha empezado realizando un estudio del sector y de su funcionamiento así como de la evolución reciente del mercado tanto en Europa como en España. Posteriormente se ha modelizado una planta de biodiesel tipo desde las primeras fases de su construcción hasta su puesta en funcionamiento, para, a continuación analizar su desarrollo haciendo especial hincapié en la evolución de las principales variables económicas anteriormente estudiadas que han llevado finalmente a tener que cerrarla por falta de rentabilidad. El proceso de producción del biodiésel desde aceites vegetales y grasas animales mantiene un fuerte crecimiento en los mercados de la Unión Europea al igual que en Estados Unidos y Canadá. La producción de biodiésel se ha incrementado rápidamente en los últimos años, ya que es una alternativa renovable a los carburantes, como el petróleo o el diésel. La producción por trasesterificación de aceites vegetales y grasas animales, dan al biodiésel una densidad, un punto de encendido, viscosidad, estabilidad a la oxidación similares al diésel. Estas propiedades permiten a la mezcla de biodiésel poder usarlo en motores convencionales sin necesidad de grandes modificaciones. El objetivo fundamental de este proyecto es, dentro de un entorno económico hostil, explicar el posible porqué de la situación de las plantas de biodiésel en España, haciendo un análisis de la viabilidad económico – financiera de una planta de producción de biodiésel. La instalación de la que parte el presente proyecto es la de una planta, situada en la provincia de Jaén, con una capacidad de producción de 100 000 t/año, con una previsión de funcionamiento continua y con una vida útil estimada de 15 años. Una vez finalizado el estudio económico, se ha valorado el impacto del mercado en el funcionamiento de la planta, tanto a nivel internacional debido a la competencia desleal, como nacional, debido a las ayudas en los cultivos. Se deduce que la rentabilidad de una planta de biodiésel es relativamente positiva pero viene dada por un gran número de variables internas y externas que hacen un negocio inestable y poco rentable. ABSTRACT It explains the possible reasons that have forced several biodiesel plants in Spain to close in spite of being sponsored by the European Union and promoted by specific regulations and substantial aid in each of the member countries to strengthen the use of biofuels as alternative energy to fossil fuels because of the environmental and sociopolitical involving VII For this we have begun a study of the sector and its operation as well as the recent market developments in Europe and in Spain. Later was modeled biodiesel plant type from the early stages of construction to commissioning, to then analyze its development with particular emphasis on the evolution of the main economic variables that have been previously studied eventually have to close by unprofitability. The processes and production of biodiesel (methyl ester) from vegetable oil and animal fat feedstocks remain a strong growth market in the European Union as well as the United States and Canada. Biodiesel production has increased rapidly in this last years as producers sought a renewable alternative to petroleum fuel. Produced by the trans-esterification of vegetable oils and animal fats, biodiesel has similar density, flash point, viscosity, oxidation stability to petroleum diesel. These similarities enable biodiesel blends to be used in conventional diesel engines without significant modifications. This proyect gives an overview of current developments with regard to biodiesel technology, the Spain biofuel market, and national biofuel policies, looking at closely the economic-financial feasibility of a biodiesel production plant. The installation, situated at Linares (Jaén), has a production capability of 100 000 t/year. The operation estimated is constant and with a product life of 15 years. Finished the part destined to the economic view of this project, it has been considered the adverse effects on the overall performance and the financial situation of the industry. It follows form the study that biodiesel plant´s profitability is relatively high, but it is given by a large numbers of variables, internals and externals, which have made an unviable and unsustainable business.

PAH occurrence during combustion of biodiesel from various feedstocks

PAHs are pollutants of concern since they are known carcinogenic compounds. Their occurrence is mainly related to combustion or pyrolysis of organic matter such as fossil fuels. In the current scenario where biofuels are growingly important, it is also necessary to characterize PAH emissions due to their combustion. There are a number of works concerning PAH emissions from biodiesel combustion in Diesel engines, however, there are few regarding the difference between them depending on the feedstock and type of alcohol used in the transesterification. The authors have processed and characterized biodiesel from several feedstocks (Le. tallow, palm, rapeseed, soy-bean, coconut, peanut and linseed oils) to obtain FAME and FAEE and they have developed a method to measure the PAHs originated during their combustion in a bomb calorimeter. The tests have been carried out under different oxygen pressure conditions, and samples have been c1eaned from the bomb after each one of these tests. The samples have been prepared for GC-MS analysis, where PAH quantities among some other combustion products have been assessed. This work shows statistical relations obtained between the measured amounts of 18 PAHs of concern and the composition (oil and type of alcohol) used to obtain the biodiesel, and also the oxygen pressure during combustion.

Aplicación distribuida para la monitorización y diagnosis de automóviles

En este proyecto se va desarrollar una aplicación distribuida para la diagnosis y monitorización de automóviles. Se pretende poder realizar estas funciones en prácticamente cualquier automóvil del mercado (con fabricación a partir del año 1996 para el caso de automóviles gasolina y para el año 2000 en el caso de automóviles diésel) de manera remota, aprovechando la conectividad a Internet que actualmente brindan la mayoría de los smartphones. La viabilidad del proyecto reside en la existencia de estándares para la diagnosis de la electrónica del motor. Para poder llevar a cabo esta tarea, se empleará una interfaz de diagnóstico ELM327 bluetooth, que servirá de enlace entre el vehículo y el teléfono móvil del usuario y que a su vez se encargara de enviar los datos que reciba del vehículo a un terminal remoto. De esta manera, se tendrá la aplicación dividida en dos partes: por un lado la aplicación que se ejecuta en el terminal móvil del usuario que actuará como parte servidora, y por el otro la aplicación cliente que se ejecutará en un terminal remoto. También estará disponible una versión de la aplicación servidora para PC. El potencial del proyecto reside en la capacidad de visualización en tiempo real de los parámetros más importantes del motor del vehículo y en la detección de averías gracias a la funcionalidad de lectura de la memoria de averías residente en el vehículo. Así mismo, otras funcionalidades podrían ser implementadas en posteriores versiones de la aplicación, como podría ser el registro de dichos parámetros en una base de datos para su posterior procesado estadístico; de este modo se podría saber el consumo medio, la velocidad media, velocidad máxima alcanzada, tiempo de uso, kilometraje diario o mensual… y un sin fin de posibilidades. ABSTRACT. In this project a distributed application for car monitor and diagnostic is going to be developed. The idea is to be able to connect remotely to almost any car (with production starting in 1996 in the case of petrol engines and production starting in 2000 in case of diesel engines) using the Internet connection available in almost every smartphone. The project is viable because of the existence of standards for engine electronic unit connection. In order to do that, an ELM327 bluetooth interface is going to be used. This interface works as a link between the car and the smartphone, and it is the smartphone which sends the received data from the car to a remote terminal (computer). Thus, the application is divided into two parts: the server which is running on smartphone and the client which is running on a remote terminal. Also there is available a server application for PC. The potential of the project lies in the real-time display data capacity of the most important engine parameters and in the diagnostic capacity based on reading fault memory. In addition, other features could be implemented in later versions of the application, as the capacity of record data for future statistic analysis. By doing this, it is possible to know the average fuel consumption, average speed, maximum speed, time of use, daily or monthly mileage… and an endless number of possibilities.

Recubrimientos autolubricantes cuasicristalinos tipo composite depositados mediante proyección térmica para aplicaciones espaciales y de alta temperatura

Los recubrimientos lubricantes sólidos son requeridos para reducir la fricción y prevenir el desgaste en componentes que operan a altas temperaturas o en vacío (vehículos espaciales, industria química, motores diésel, turbinas aeronáuticas y de generación de energía…). Los lubricantes líquidos pierden sus características cuando las condiciones de presión, temperatura o ambientales son severas (oxidación, inestabilidad térmica, volatilidad,…), por ejemplo los aceites minerales convencionales se descomponen a temperaturas próximas a 200 ºC. Por tanto, la única manera de poder conseguir una adecuada lubricación a temperaturas extremas es por medio de sólidos, que cada vez más, se aplican en forma de recubrimientos. Estos recubrimientos podrían ser empleados en componentes de vehículos espaciales reutilizables, donde se pueden alcanzar, en la reentrada en la atmósfera, temperaturas de 700 ºC (bisagras, rodamientos, articulaciones y zonas de sellado en las superficies de control, y rodamientos de las turbobombas y las cajas de engranajes). Dichos recubrimientos también deberían ser capaces de proporcionar una lubricación efectiva a bajas temperaturas para las operaciones en tierra, para las operaciones de arranque en frío, incluso en el espacio. El conjunto de requisitos que tendrían que satisfacer las capas tribológicas relacionadas con estas condiciones extremas es muy diverso, lo que hace que el concepto de capas tipo composite (aquéllas constituidas por varios componentes) sea, en principio, muy adecuado para estas aplicaciones. Recubrimientos composite proyectados térmicamente constituidos por una matriz dura y conteniendo lubricantes sólidos pueden ser una buena solución desde el punto de vista tribológico. El “Lewis Research Centre” de la NASA ha estado desarrollando recubrimientos autolubricantes tipo composite, constituidos por la combinación de materiales duros como el carburo de cromo, junto con lubricantes sólidos como plata o la eutéctica de fluoruros de calcio y bario, en una matriz de NiCr, para su uso en aplicaciones terrestres a alta temperatura. Estos recubrimientos han sido aplicados mediante proyección térmica, siendo denominados como series PS100, PS200, PS300 y PS400, reduciendo de forma significativa el coeficiente de fricción y mejorando la resistencia al desgaste en un amplio margen de temperaturas. Otra nueva familia de materiales con comportamiento tribológico prometedor son las aleaciones cuasicristalinas (QC). Presentan características muy atractivas: alta dureza, baja fricción, alto límite elástico de compresión... Son muy frágiles como materiales másicos, por lo que se intentan aplicar en forma de recubrimientos. Se pueden depositar mediante proyección térmica. Algunos de estos materiales cuasicristalinos, como AlCoFeCr, poseen coeficientes de dilatación próximos al de los materiales metálicos, alta estabilidad térmica, baja conductividad térmica y una elevada resistencia a la oxidación y a la corrosión en caliente. En esta tesis se han desarrollado recubrimientos tipo composite conteniendo cuasicristales como componente antidesgaste, NiCr como componente tenaz, y Ag y la eutéctica de BaF2-CaF2, como lubricantes sólidos. Estos recubrimientos han sido depositados con diferentes composiciones (denominadas TH100, TH103, TH200, TH400, TH600…) mediante distintos procesos de proyección térmica: plasma en aire (PS), plasma en baja presión (LPPS) y combustión a alta velocidad (HVOF). Los recubrimientos se han generado sobre el sustrato X-750, una superaleación base níquel, endurecible por precipitación, con muy buena resistencia mecánica y a la oxidación hasta temperaturas de 870 ºC y, además, es empleada en aplicaciones aeroespaciales e industriales. Los recubrimientos han sido caracterizados microestructuralmente en INTA (Instituto Nacional de Técnica Aeroespacial), mediante SEM-EDS (Scanning Electronic Microscopy-Energy Dispersive Spectroscopy) y XRD (X-Ray Diffraction), y tribológicamente mediante medidas de microdureza y ensayos en tribómetro POD (Pin On Disc) para determinar los coeficientes de fricción y de desgaste. Los recubrimientos han sido ensayados tribológicamente a alta temperatura en INTA y en vacío en AMTTARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), en Seibersdorf (Austria). Se ha estudiado la influencia de la carga normal aplicada, la velocidad lineal y el material del pin. De entre las diferentes series de recubrimientos cuasicristalinos tipo composite desarrolladas, dos de ellas, TH100 y TH103 han presentado una excelente calidad microestructural (baja porosidad, distribución uniforme de fases…) y se han mostrado como excelentes recubrimientos antidesgaste. Sin embargo, estas capas presentan un pobre comportamiento como autolubricantes a temperatura ambiente, aunque mejoran mucho a alta temperatura o en vacío. Los resultados del trabajo presentado en esta tesis han proporcionado nuevo conocimiento respecto al comportamiento tribológico de recubrimientos autolubricantes cuasicristalinos tipo composite depositados por proyección térmica. Sin embargo, dichos resultados, aunque son muy prometedores, no han puesto de manifiesto el adecuado comportamiento autolubricante que se pretendía y, además, como ocurre en cualquier trabajo de investigación, durante el desarrollo del mismo siempre aparecen nuevas dudas por resolver. Se proponen nuevas líneas de trabajo futuro que complementen los resultados obtenidos y que puedan encaminar hacia la obtención de un recubrimiento que mejore su comportamiento autolubricante. ABSTRACT Solid lubricant coatings are required to reduce friction and prevent wear in components that operate at high temperatures or under vacuum (space vehicles, chemical industry, diesel engines, power generation turbines and aeronautical turbines, for instance). In these cases neither greases nor liquid lubricants can be employed and the only practicable approach to lubrication in such conditions is by means of solids. These are increasingly applied in the form of coatings which should exhibit low shear strength, whilst maintaining their chemical stability at extremes temperatures and in the space environment. In the space field, these coatings would be employed in re-usable space plane applications, such as elevon hinges, where temperatures of 700 ºC are reached during re-entry into the Earth’s atmosphere. These coatings should also be capable of providing effective lubrication at lower temperatures since “cold start” operation may be necessary, even in the space environment. The diverse and sometimes conflictive requirements in high temperature and space-related tribological coatings make the concept of composite coatings highly suitable for these applications. Thermal-sprayed composites containing solid lubricants in a hard matrix perform well tribologically. NASA‘s Lewis Research Centre had developed self-lubricating composite coatings for terrestrial use, comprising hard materials like chromium carbide as well as solid lubricant additives such as silver and BaF2-CaF2 eutectic on a Ni-Cr matrix. These coatings series, named PS100, PS200, PS300 and PS400, are applied by thermal spray and significantly reduce friction coefficients, improving wear resistance over a wide temperature range. Quasicrystalline alloys (QC) constitute a new family of materials with promising tribological behaviour. Some QC materials exhibit a combination of adequate antifriction properties: low friction coefficient, high hardness and high yield strength under compression, and can be easily produced as coatings on top of metallic and non-metallic materials. Among these QC alloys, AlCoFeCr has high hardness (700 HV0.1), a thermal expansion coefficient close to that of metals, high thermal stability, low thermal conductivity and good oxidation and hot corrosion resistance. However most QC materials have the disadvantage of being very brittle. In order to take advantage of the excellent tribological properties of QCs, thick composite lubricant coatings were prepared containing them as the hard phase for wear resistance, Ag and BaF2-CaF2 eutectic as lubricating materials and NiCr as the tough component. These coatings were deposited in different composition mixtures (named TH100, TH103, TH200, TH400, TH600…) by different thermal spray processes: air plasma spray (PS), low pressure plasma spray (LPPS) and high velocity oxy-fuel (HVOF), on X-750 substrates. X-750 is an age-hardenable nickel-base superalloy with very good strength and a good resistance to oxidising combustion gas environments at temperatures up to about 870 ºC and it is widely used in aerospace and industrial applications. Coatings have been characterized microstructurally, at INTA (National Institute for Aerospace Technology), by means of SEM-EDS (Scanning Electronic Microscopy- Energy Dispersive Spectroscopy) and XRD (X-Ray Diffraction), and tribologically by microhardness measurements and pin-on-disc testing to determine friction coefficients as well as wear resistance. The coatings were tested tribologically at high temperature at INTA and under vacuum at AMTT-ARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), in Seibersdorf (Austria). Different loads, linear speeds and pin materials were studied. TH100 and TH103 QC alloy matrix composite coatings were deposited by HVOF with excellent microstructural quality (low porosity, uniform phase distribution) and showed to be excellent wear resistant coatings. However these QC alloy matrix composite coatings are poor as a self-lubricant at room temperature but much better at high temperature or in vacuum. The results from the work performed within the scope of this thesis have provided new knowledge concerning the tribological behavior of self-lubricating quasicrystalline composite coatings deposited by thermal spraying. Although these results are very promising, they have not shown an adequate self-lubricating behavior as was intended, and also, as in any research, the results have in addition raised new questions. Future work is suggested to complement the results of this thesis in order to improve the selflubricating behaviour of the coatings.

Estudo do comportamento eletroquímico da liga UNS N07090 em diferentes concentrações de ácido sulfúrico.

Ligas de níquel têm atualmente uma vasta gama de aplicações, sendo a agressividade do meio e as elevadas temperaturas que estas ligas suportam, um diferencial excepcional. A liga UNS N07090, objeto deste trabalho, encontra aplicações muito diversas, entre elas turbocompressores, sistemas de exaustão e de pós-tratamento de motores a diesel. Nestas aplicações a liga está exposta a gases, que ao condensarem formam ácido sulfúrico (H2SO4). Torna-se, assim, importante, o conhecimento da resistência à corrosão da liga nesse meio. O presente trabalho tem como objetivo caracterizar o comportamento eletroquímico da liga através de curvas de polarização potenciodinâmica em diferentes concentrações de ácido sulfúrico. Observou-se que quanto maior a concentração de ácido, maior é a corrosão da liga. Este fato pode ser discutido pela adsorção do íon sulfato (SO42-), que prejudica tanto a formação quanto a cinética de crescimento da película passiva do níquel. Em contrapartida, a presença de Cr na liga UNS N07090 apresentou um benefício sobre a resistência à corrosão desta muito acima do esperado, influenciando de forma direta as curvas de polarização da liga e mantendo-a em condição de elevada resistência à corrosão em detrimento do pior desempenho observado em outros elementos pertecentes à liga, como Co, Al e Ti. Tempos de imersão de 24h em ácido sulfúrico elevam discretamente os parâmetros de corrosão da liga, mantendo-os, no entanto em patamares bastante baixos, permitindo finalmente concluir que a liga UNS N07090, quando exposta a concentrações que variam de 1M a 4M H2SO4, a 25°C, apresenta boa resistência à corrosão e que esta não se altera com o tempo de exposição. A análise dos resultados mostrou que o processo corrosivo é controlado por reações catódicas de sulfato e hidrogênio, as quais podem ter diferentes contribuições dependendo da concentração do ácido e do tempo de imersão da liga UNS N07090 no meio corrosivo.

Augmentation of research and analysis capabilities for timely support of automotive fuel economy activities. Final report.

National Highway Traffic Safety Administration, Washington, D.C.