Dissertations / Theses on the topic 'Turbocharger'

Turbocharger performance maps are vital components used in an engine-turbocharger matching process, a 1D engine performance development stage and a day-to-day operation of a turbocharged vehicle. The main aim of this thesis is the investigation of the turbocharger compressor performance when operating with an alternative to air substitute gas. This occurs, for instance, when turbocharging and low pressure exhaust gas recirculation (LP EGR) technologies are combined. To conduct the experimental study of the turbocharger performance with substitute gas a steady-state turbocharger test facility with a compressor closed-loop mode has been designed and built within this thesis by the author. Also, for the most accurate performance map determination an uncertainty analysis of a selected turbocharger performance map and an extensive study on surge have also been carried out. The sensor based uncertainty analysis has been a key aspect to help to understand the links between the accuracy of measured quantities and the overall uncertainty of the performance parameters. Such knowledge allowed for a selection of sensors targeting the most accurate data measurement. While investigating the uncertainty of the turbocharger performance maps heat transfer related efficiency uncertainty was also studied. Namely, a series of a semi-adiabatic tests were performed in the low turbocharger speed region which highlighted the issues related to a work and heat transfer separation and uncertainty of the extrapolated performance data. Also, a contribution to the turbocharger heat transfer modelling has been made by supporting the in-house lumped capacitance thermal node model with the 3D CHT (conjugate heat transfer) simulations [1, 2]. Finally, a study of a literature based compressor heat estimation method was performed as an alternative way of separating work and heat transfer (with low speed adiabatic mapping). The experimental surge study was conducted in phases and included the analysis and comparison of the low and high frequency pressure data gathered at various locations downstream and upstream from the compressor and temperature data collected at close distance from impeller eye. It has been concluded that the post-compressor located pressure measurement is preferable (than the pre-compressor pressure measurement) as the FFT (Fast Fourier Transform) magnitude of the peak frequency associated with surge is independent on the distance of the sensor from the compressor. The useage of the temperature sensor installed at the closest distance from the compressor entry allowed an observation of the near surge temperature rise (a result of the air recirculation). However, due to the inconsistent rate of the temperature rise across the various speed lines along with the poor response it offers no benefit from the surge avoidance point of view. The comparison of the available surge metrics revealed that the resultant surge lines were drawn at different operating points especially at the higher turbocharger speed lines where the surge development investigated by the rise of the low frequency FFT magnitude peaks was much more visible. The experimental tests performed in steady-state and pulsating flow conditions have indicated larger surge margin availability for the latter case [3]. Development of a turbocharger rig and gaining the confidence in turbocharger performance map generation allowed the author to carry out the investigation over compressor performance with a substitute gas. The study covered two cases of homogeneous and non-homogeneous gas introduction representing a well and a poorly mixed gases respectively. The substitute gas included various mixtures of CO2 and air and pure CO2. It has been highlighted that when comparing turbomachinery performance maps working with substitute gas non-dimensional speed and mass flow parameters shall be introduced. These parameters allow for the map corrections with respect to individual gas constant (R) and ratio of specific heats (γ). The experimentally obtained compressor performance maps with low CO2 concentration in CO2-air mixtures (3%, 5% and 10%) were successfully corrected with the use of non-dimensional speed and mass flow parameters. However, the compressor performance map obtained for the pure CO2 has revealed significant offsets in pressure ratio, efficiency, surge and choke flow locations. This is due to a significantly different γ. In the attempt of the further performance correction a method proposed by Roberts and Sjolander has been followed. As a result of such, a poor match between the measured and predicted values of compressor efficiency was achieved (n exponent = 0.8). A closer correlation was obtained if the n exponent was made a speed dependent variable. This observation has suggested that the measurement of compressor efficiency was affected by the heat transfer between the uninsulated turbomachinery components. Due to the time limitations this assertion has not been investigated experimentally. Realising this limitation, therefore, a series of adiabatic CFD simulations have been performed instead. These simulations have shown that for the case of pure CO2 a reasonable match between the simulated and predicted values of efficiency and pressure ratio was achieved. The experimental and numerical comparison of the compressor performance for homogeneously and non-homogeneously introduced substitute gas did not show any significant compressor performance changes. Finally, experimental study of selected configurations of the intake pipework and EGR mixing valve has shown that complex flow regimes can be developed within the LP EGR system affecting the compressor’s surge margin, efficiency and width of the map. This demonstrates that the aerodynamic disturbances of an EGR mixing valve may have the largest influence on the compressor map compared to all other factors.

A programme of research was undertaken to identify the mechanisms of formation of voids and defects in aluminium alloy C354 and C355 castings. The following aspects of the material processing were studied as independent and linked effects: casting technique and associated variables, hot isostatic pressing cycle parameters, and heat treatment cycle. Microstructure related driving forces for defect formation were quantified using differential scanning calorimetry and quantitative metallography and surface effects investigated using x-ray photoelectron spectroscopy. It was shown that by controlling key variables within casting, the component can become less sensitive to subsequent defect evolution from further thermal processing. Optimised parameters were defined and the mechanism of defect formation elucidated. A Non Destructive Testing (NDT) method for the detection of defects within C354 components was developed.

As turbocharging requirements raise to face an increasingly stricter environmental regulation of internal combustion engines, concerns regarding their acoustic emission become more pressing. Since downsized engines require higher boost pressures and lower mass flow rates, the turbocharger compressor is forced to work at more unstable regimes, where flow patterns become more complex and noise levels rise. This thesis aims to thus to investigate these issues, proposing methodologies to characterize the acoustic emission of turbocharger compressors and implementing them in different experiments with a special focus on the link between acoustic emission and flow behaviour at unstable conditions. A literature review is carried out in order to assess the state of the art principally regarding experimental techniques related to this issue but also including the latest developments in terms of understanding the flow characteristics through numerical simulations. Different methodologies are consequently proposed and implemented into a custom test rig inside an anechoic chamber as to experimentally measure and analyze the acoustic output of the compressor. From this measurement campaign a characterization of the noise spectral content across the compressor map is obtained and described, identifying different acoustical phenomena such as blade passing tonal noise, low frequency content associated to deep surge, higher frequency broadband ascribed to tip clearance interaction, and broadband noise in the plane wave range known as whoosh in the literature, of special concern for automotive manufacturers. This particular phenomenon is detected even at more stable conditions at higher flow rate, and rising in level as flow rate is diminished to the point of being masked by lower frequency content. After a validation of the selected procedure in realistic engine conditions, experimental data is compared against a numerical model of the compressor developed in a parallel work to assess its validity and propose different post-processing techniques to extract additional insights about the behaviour of the flow at different conditions, hinting at the main generation mechanism for whoosh being located at the compressor diffuser. Since numerical simulations predict a reduced amount of reversed unstable flow at conditions where whoosh noise is still measured, an experimental campaign is performed where detailed measures of local temperature near the compressor wheel are used to determine the evolution of reversed flow, with supplemental readings through pressure probes in the inducer and diffuser being used to link this evolution with the fluctuation of spectral content. Temperature results are also correlated with measurements of the velocity field through particle imaging, demonstrating a clear link between the reversed flow field and temperature readings. Different experimental campaigns are then described where modifications of the inlet geometry immediately upstream the compressor are performed in order to assess how the air flow presentation can influence acoustic performance. Geometries featuring reservoirs, nozzles and guide vanes are shown to potentially reduce noise levels. A 90º elbow parametric study is performed, demonstrating how the inner radius of the elbow influences circumferential temperature differences and noise levels, leading to the hypothesis of geometry influence on whoosh noise being related to air presentation changes that promote lower or higher growth of reversed backflow, which in turns carries upstream the spectral content being generated in the compressor diffuser.
A medida que los requerimientos de turbocompresión aumentan para afrontar una regulación de los motores de combustión interna cada vez más estricta, la preocupación respecto a su emisión acústica se hace más acuciante. Debido a que motores de menor tamaño requieren mayores aumentos de presión y menores gastos másicos, el compresor del turbogrupo se ve forzado a trabajar en regímenes más inestables, los patrones de flujo se hacen más complejos y los niveles de ruido aumentan. Esta tesis tiene como objetivo investigar estas cuestiones, proponiendo metodologías para caracterizar la emisión acústica de compresores de turbogrupos, e implementándolas en diferentes experimentos enfocados especialmente en la relación entre emisión acústica y comportamiento del flujo en condiciones inestables. Por tanto, se lleva a cabo una revisión bibliográfica para evaluar el estado del arte, especialmente en lo concerniente a técnicas experimentales relacionadas con el problema, pero incluyendo también los últimos desarrollos en términos de comprensión de las características del flujo mediante simulaciones numéricas. Como resultado, diferentes metodologías se proponen e implementan en un banco de ensayo hecho a medida dentro de una cámara anecoica para medir y analizar la producción sonora del compresor. Mediante esta campaña de medida se obtiene y describe una caracterización acústica del contenido espectral del ruido a lo largo del mapa del compresor, identificando diferentes fenómenos sonoros tales como ruido tonal debido al paso de álabe, contenido de baja frecuencia asociado al bombeo profundo, contenido de banda ancha a alta frecuencia atribuido a la interacción del flujo en la holgura de punta de pala y ruido de banda ancha en el rango de onda plana, conocido como whoosh en la literatura y de especial interés para los fabricantes automovilísticos. Este fenómeno en concreto se detecta incluso a condiciones más estables de alto gasto másico, y aumenta de nivel a medida que el gasto disminuye hasta llegar a ser enmascarado por el aumento del contenido de baja frecuencia. Después de validar los procedimientos seleccionados en condiciones realistas de motor, se comparan los datos experimentales con un modelo numérico del compresor desarrollado en un trabajo paralelo a fin de evaluar su validez y proponer diferentes técnicas de postprocesado, con el objetivo de extraer información adicional acerca del comportamiento del flujo en diferentes condiciones, que sugieren que el mecanismo principal de generación de whoosh se encuentra localizado en el difusor del compresor. Se lleva a cabo una campaña experimental en la cual medidas detalladas de temperatura local cerca del rotor se usan para determinar la longitud del flujo inverso, con medidas suplementarias a través de sondas de presión usadas para relacionar esta evolución con la fluctuación de contenido espectral. Los resultados de temperatura se correlacionan también con medidas del campo de velocidad por imágenes de partículas, demostrando una clara relación entre el campo de flujo inverso y las medidas de temperatura. Se describen a continuación diferentes campañas experimentales en las cuales se llevaron a cabo modificaciones de la geometría de entrada inmediatamente aguas arriba del compresor con el fin de evaluar cómo la presentación del flujo puede influenciar el rendimiento acústico. Geometrías incluyendo remansos, toberas y álabes guía demuestran una reducción de los niveles de ruido. Se ha realizado un estudio paramétrico de un codo de 90º, mostrando que el radio del codo influye en la distribución circunferencial de temperatura y los niveles de ruido, llevando a la hipótesis de que la influencia de la geometría en el ruido de whoosh está relacionada con cambios en la presentación del aire que promueven menor o mayor reflujo, que a su vez convecta aguas arriba el contenido espectral generado en el difusor del
A mesura que els requeriments de turbocompressió augmenten a fi d'afrontar una regulació dels motors de combustió interna cada vegada més estricta, la preocupació respecte a la seva emissió acústica es fa més urgent. Com que motors de dimensions més reduïdes requereixen majors augments de pressió i menors cabals màssics, el compressor del turbogrup es veu forçat a treballar a règims més inestables, els patrons de flux es fan més complexos, i els nivells de soroll augmenten. Aquesta tesi té com a objectiu investigar aquestes qüestions, proposant metodologies per a caracteritzar l'emissió acústica de compressors de turbogrups, implementant-les en diferents experiments enfocats especialment a la relació entre emissió acústica i comportament del flux en condicions inestables. Per tant, es duu a terme una revisió bibliogràfica per avaluar l'estat de l'art, especialment pel que fa a tècniques experimentals relacionades amb el problema, però incloent també els últims desenvolupaments en termes de comprensió de les característiques del flux mitjançant simulacions numèriques. Com a resultat, diferents metodologies es proposen i implementen en un banc d'assaig fet a mida dins d'una cambra anecoica per mesurar i analitzar la producció sonora del compressor. Mitjançant aquesta campanya de mesura s'obté i descriu una caracterització acústica del contingut espectral del soroll al llarg del mapa del compressor, identificant diferents fenòmens sonors com ara soroll tonal a causa del pas d'àlep, contingut de baixa freqüència associat al bombeig profund, contingut de banda ampla a alta freqüència atribuït a la interacció del flux en la folgança de punta de pala i soroll de banda ampla en el rang d'ona plana, conegut com a whoosh en la literatura i d'especial interès per als fabricants automobilístics. Aquest fenomen en concret es detecta fins i tot a condicions més estables d'alt cabal màssic, i augmenta de nivell a mesura que el cabal disminueix fins arribar a ser emmascarat per l'augment del contingut de baixa freqüència. Després de validar els procediments seleccionats en condicions realistes de motor, es comparen les dades experimentals amb un model numèric del compressor desenvolupat en un treball paral·lel a fi d'avaluar la seva validesa i proposar diferents tècniques de post-processat, amb l'objectiu d'extraure informació addicional sobre el comportament del flux en diferents condicions, que suggereixen que el mecanisme principal de generació de whoosh es troba localitzat al difusor del compressor. Pel fet que nombroses simulacions prediuen una quantitat reduïda de'inestable flux invers en condicions on el whoosh apareix en les mesures, es duu a terme una campanya experimental en la qual mesures detallades de temperatura local prop del rotor s'utilitzen per a determinar la longitud del flux invers, amb mesures suplementàries mitjançant sondes de pressió emprades per a relacionar aquesta evolució amb la fluctuació de contingut espectral. Els resultats de temperatura es correlacionen també amb mesures del camp de velocitat per imatges de partícules, demostrant una clara relació entre el camp de flux invers i les mesures de temperatura. Es descriuen a continuació diferents campanyes experimentals en les quals es van realitzar modificacions de la geometria d'entrada immediatament aigües dalt del compressor a fi d'avaluar com la presentació del flux pot influenciar el rendiment acústic. Geometries incloent volums, toveres i àleps guia demostren una reducció dels nivells de soroll. S'ha realitzat un estudi paramètric d'un colze de 90º, mostrant que el ràdio del colze influïx en la distribució circumferencial de temperatura i els nivells de soroll, donant suport a la hipòtesi de que la influència de la geometria en el soroll de whoosh està relacionada amb canvis en la presentació de l'aire que promouen menor o major reflux, que aleshores convecta aigües da
García Tíscar, J. (2017). Experiments on turbocharger compressor acoustics [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/79552
TESIS

Heat transfer plays an important role in affecting an on-engine turbocharger performance. However, it is normally not taken into account for turbocharged engine simulations. Generally, an engine simulation based on one-dimensional gas dynamics uses turbocharger performance maps which are measured without quantifying and qualifying the heat transfer, regardless of the fact that they are measured on the hot-flow or cold-flow gas-stand. Since heat transfer situations vary for on-engine turbochargers, the maps have to be shifted and corrected in the 1-D engine simulation, which mass and efficiency multipliers usually do for both the turbine and the compressor. The multipliers change the maps and are often different for every load point. Particularly, the efficiency multiplier is different for every heat transfer situation on the turbocharger. The heat transfer leads to a deviation from turbocharger performance maps, and increased complexity of the turbocharged engine simulation. Turbochargers operate under different heat transfer situations while they are installed on the engines. The main objectives of this thesis are: heat transfer modeling of a turbocharger to quantify and qualify heat transfer mechanisms, improving turbocharged engine simulation by including heat transfer in the turbocharger, assessing the use of two different turbocharger performance maps concerning the heat transfer situation (cold-measured and hot-measured turbocharger performance maps) in the simulation of a measured turbocharged engine, prediction of turbocharger walls’ temperatures and their effects on the turbocharger performance on different heat transfer situations. Experimental investigation has been performed on a water-oil-cooled turbocharger, which was installed on a 2-liter GDI engine for different load points of the engine and different heat transfer situations on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. In addition, several thermocouples have been used on accessible surfaces of the turbocharger to calculate external heat transfers. Based on the heat transfer analysis of the turbocharger, the internal heat transfer from the bearing housing to the compressor significantly affects the compressor. However, the internal heat transfer from the turbine to the bearing housing and the external heat transfer of the turbine housing mainly influence the turbine. The external heat transfers of the compressor housing and the bearing housing, and the frictional power do not play an important role in the heat transfer analysis of the turbocharger. The effect of the extra cooling fan on the energy balance of the turbocharger is significant. However, the effect of the water is more significant on the external heat transfer of the bearing housing and the internal heat transfer from the bearing housing to the compressor. It seems the radiation shield between the turbine and the compressor has no significant effect on the energy balance of the turbocharger. The present study shows that the heat transfer in the turbocharger is very crucial to take into account in the engine simulations. This improves simulation predictability in terms of getting the compressor efficiency multiplier equal to one and turbine efficiency multiplier closer to one, and achieving turbine outlet temperature close to the measurement. Moreover, the compressor outlet temperature becomes equal to the measurement without correcting the map. The heat transfer situation during the measurement of the turbocharger performance influences the amount of simulated heat flow to the compressor. The heat transfer situation may be defined by the turbine inlet temperature, oil heat flux and water heat flux. However, the heat transfer situation on the turbine makes a difference on the required turbine efficiency multiplier, rather than the amount of turbine heat flow. It seems the turbine heat flow is a stronger function of available energy into the turbine. Of great interest is the fact that different heat situations on the turbocharger do not considerably influence the pressure ratio of the compressor. The turbine and compressor efficiencies are the most important parameters that are affected by that. The component temperatures of the turbocharger influence the working fluid temperatures. Additionally, the turbocharger wall temperatures are predictable from the experiment. This prediction enables increased precision in engine simulations for future works in transient operations.
QC 20120504

The purpose with this Masters Thesis was to design a measurement rig for measurement of the blowby flow that originates from the turbocharger in a passenger car engine. A leakage of com-bustion gases and fresh air from the turbine and the compressor into the bearing housing of the turbocharger is the source of the blowby flow. Principally the measurement rig consists of two parts: a flowmeter for measurement of the blowby flow and a separation unit for separation of the blowby gases from the engine oil that is used for the lubrication of the bearings in the turbo-charger. The rig will be connected between the return oil pipe from the turbocharger and the en-gines crankcase and should only be used in engine testcells. First, an extensive study of different methods for measurement of gas flow and separation of gas and oil was carried out. Methods that best fulfill the set specifications of requirements are chosen to be used in the rig. From the results of the study a conclusion can be made that the best solu-tion is to use a flowmeter specifically made for engine blowby metering with another measure-ment pipe for more accurate measurements. A tank is used for the separation of oil and gas and it functions at the same time as a collecting vessel for the oil. A rack of baffle sheets inside the tank is used as the separation technique. The tank is also equipped with a pump and associated limit switches for controlling the oil level inside the tank. An oil heater is also applied to the tank for heating of the oil while kept in the tank. Testing of the equipment was executed with an engine in testcells to verify the functionality of the equipment. A test cycle that extended over the engines whole load and speed range was used. Gained results show that the turbocharger blowby follows the same pattern as the total engine blowby. It increases with higher engine load rather than with higher engine speed. It is also pos-sible to confirm that the rig has an influence on the engines blowby system, but also that the size of it is not conclusive to the measurements. A conclusion that the turbocharger blowby should not be measured simultaneously with the engine blowby can be done from the test results.
Detta examensarbete omfattar konstruerandet av en mätningsrigg för mätning av det blowby-flöde som uppstår i en personbilsturbo. Blowby-flödet består av det läckage av förbränningsgaser och friskluft som sker genom turbin och kompressor in i lagerhuset på turboladdaren. Mätnings-riggen består huvudsakligen av två delar: en separationstank för separering av blowby-gaserna från den olja som används för smörjning av turbolagringen och en gasflödesmätare. Mätningsrig-gen kopplas in mellan turbons oljereturrör och motorn och den ska endast användas i motorprov-celler. Arbetet innehåller en omfattande förstudie där olika metoder för mätning av gasflöde och separe-ring av olja och gas presenteras och diskuteras. Den mätningsmetod som väljs uppfyller bäst de ställda kraven. Resultatet från förstudien visar att den bästa mätningsmetoden är att använda en gasmätare konstruerad för blowby-mätning i motorer, men med ett annat mätrör. Separeringen av olja och gas sker inuti en tank som samtidigt fungerar som en uppsamlingsbehållare för oljan med hjälp av avrinningsplåtar. Tanken är utrustad med en pump med tillhörande styrdon samt en oljevärmare för uppvärmning av oljan i tanken. Arbetet omfattade också provning av den framtagna utrustningen för att verifiera dess funktion. Provningen utfördes med en motor i motorprovcell med en testcykel som omfattade motorns hela last- och varvtalsregister. Provningens syfte var att undersöka om det går att mäta blowby genom turboladdaren med mätningsriggen samt att bestämma hur stor påverkan mätningsriggen har på motorn. Resultatet visar att turboblowbyn följer samma mönster som den totala motorblowbyn. Den ökar mer med högre last än med högre motorvarvtal. Det kan också bekräftas att mätningsriggen har en inverkan på motorns blowby-system, men att den är så begränsad att den inte har en avgö-rande inverkan på mätningarna. Resultatet visar också att blowby-flödet genom turbon inte kan mätas samtidigt med motorblowbyn om den specificerade mätningsmetoden används.

The use of diesel engine turbochargers is increasing today, as it represents an option that o ers high e ciency and low fuel consumption. To design the control system in order to reduce the level of exhaust emissions there is a need for information about all states that are not measurable. To this end, observers or virtual sensors are more frequently applied, achieving estimates of the system states from inputs and measured output. To propose an observer, the precise mathematical model of the air path diesel engine system is used. This is a nonlinear model of a third order which is analyzed in terms of observability. From the point of view of systems theory, certain conditions and the existence of a transformation of the system state, called di eomorphism, need to be evaluated. Observers have been designed based on di erent approaches: Extended Luenberger Observers, High Gain Observers, Sliding Modes Observers and Extended Kalman-Bucy Filters. They have been validated by simulation for the system under consideration in this work.
Tesis

Thesis (MScEng)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: Stellenbosch University participated in a project to re-design the compressor section of a diesel locomotive turbocharger. Tests conducted on the prototype compressor showed possible rotating stall in the diffuser section before the designed higher pressure ratio could be achieved. When approaching the higher pressure ratio, the compressor inlet trunk started to rhythmically collapse (due to suction), the engine shook and bellows of black smoke were exhausted by the engine. It was decided to simulate the prototype compressor's operation by using the 1-D theory of Aungier (2000) and to perform a 3-D CFD analysis of the compressor using FINE/Turbo of NUMECA International. A veri cation process was followed to show the accuracy of the 1-D and 3-D modelling methods using two well-known centrifugal compressor test cases found in the literature, namely the O-Rotor by Eckardt (1975, 1976, 1980) and the "Radiver" open CFD test case by Ziegler et al. (2003c). Results from the models were compared to available experimental results and the accuracy was found to be su cient to investigate the prototype compressor's impeller and diffuser. Both prediction methods con rmed separation in the vaned di user across the entire operating ow range of the prototype compressor at the design impeller speed. The 3-D method identi ed supersonic ow at the vaned diffuser inlet at the operating point and also predicted a smaller operating range than originally anticipated. Both the 1-D and 3-D methods also predicted impeller blade stall over the entire operating ow range at the design impeller speed. A recommendation was made to redesign the impeller and diffuser of the prototype compressor.
AFRIKAANSE OPSOMMING: Die Universiteit van Stellenbosch het deel geneem aan 'n projek om die kompressor gedeelte van 'n diesel lokomotief se turbo-aanjaer te herontwerp. Toetse uitgevoer op die prototipe kompressor het moontlike roterende wegbreking in die diffuser seksie uitgewys voordat die ontwerpte hoër drukverhouding bereik kon word. Toe die hoër drukverhouding genader is, het die kompressor inlaatpyp begin ritmies inmekaar vou (as gevolg van die suig aksie), die enjin het geskud en wolke swart rook is deur die enjin uitgeblaas. Die besluit is geneem om die prototipe kompressor se werking te simuleer met behulp van die 1-D teorie van Aungier (2000) en om ook 'n 3-D berekenings vloeimeganika (BVM) analise op die kompressor uit te voer met behulp van FINE/Turbo van NUMECA Internasionaal. 'n Veri kasieproses is gevolg om die akkuraatheid van die 1-D en 3-D modelle te illustreer met behulp van twee welbekende sentrifugaal kompressor toetsgevalle beskikbaar in die literatuur, naamlik die O-Rotor deur Eckardt (1975, 1976, 1980) en die "Radiver" oop BVM toetsgeval deur Ziegler et al. (2003c). Resultate van die modelle is vergelyk met beskikbare eksperimentele resultate en die bevinding is gemaak dat die akkuraatheid genoegsaam is om die prototipe kompressor se rotor en diffuser te ondersoek. Beide voorspellingsmetodes het wegbreking bevestig in die gelemde diffuser oor die hele werksbestek van die prototipe kompressor teen die ontwerp rotorspoed. Die 3-D metode het supersoniese vloei by die gelemde diffuser se inlaat by die bedryfspunt geïdenti seer en het ook 'n kleiner werksbestek voorspel as wat vroeër verwag is. Beide die 1-D en 3-D metodes het ook wegbreking in die rotor oor die hele werksbestek teen die ontwerp rotorspoed voorspel. 'n Voorstel is gemaak om die rotor en diffuser van die prototipe kompressor te herontwerp.

Turbocharging is a way to stay competitive on the market where there are increasing demands on fuel consumption and engine performance. Turbocharging lets the engine work closer to its maximum power and thereby reduces the relative losses due to pumping and friction. The turbocharger is exposed to big temperaturedifferences and heat flows will occur both internally between the turbine and the compressor as well as between the turbocharger and its surroundings. Away to get a better understanding of the behaviour of the turbocharger is to understand the heat flows better. This thesis is therefore aimed at investigating theeffect of heat transfer on the turbocharger. In the thesis, different ways of accountfor the heat transfer within the turbocharger is investigated and a heat transfermodel is presented and validated. The model can be used as a tool to estimate theimportance of different heat flows within the turbocharger. A set of heat transfer coefficients are estimated and the heat transfer is modelled with good accuracyfor high engine loads and speeds.

The demand for CO2 emission reduction for modern road vehicles has seen engine downsizing become a key trend in internal combustion engine design: a smaller engine has reduced pumping, frictional and heat losses, and therefore better fuel economy. Turbocharger technology is one of the enabling technologies, offering lower specific fuel consumption and producing more power for a given engine capacity. The turbocharger matching process, which specifies an appropriate turbocharger design for a particular engine, is crucial in obtaining optimum engine performance. In order to achieve a high level of accuracy in the system-level prediction, high fidelity turbocharger models are required; but such models have not yet reached fruition. The present study has assessed the effect of preserving the exhaust pulse energy from an engine right through to the turbine on the steady and transient engine performance. A combination of appropriate turbine sizing and pulse-divided exhaust manifold was applied, and as a consequence, lower back pressure and improved engine scavenging reduced residual content by 28%, while the brake specific fuel consumption (BSFC) improves by approx. 1.2% on average over speed range. Furthermore, the implementation of electric turbo assist (ETA) system on the engine results in better fuel economy by 2.4%. The present work has also assessed the overall engine performance using a commercial 1-D gas dynamics simulation tool by modelling the waste-gated turbines in a novel manner. This approach has been validated experimentally. The study also examined the benefits of electric turbocharger systems for a highly-downsized engine, a modified version of the baseline engine. Some potential multi-boosting systems were applied, and the overall benefits in terms of engine performance were assessed. An integration of an electric turbocharger and a low-pressure turbine with electric turbo compounding gives the best advantages particularly in pumping loss, residual and transient performance while improving fuel economy in comparison with other systems.

This thesis presents an investigation of a shroud bleed slot system of a compressor stage from a turbocharger unit used in heavy duty diesel engines of approximately 300 kW. The first part of the work presented in this thesis deals with a detailed analysis of a compressor stage with and without a shroud bleed slot, and various slot geometries which include three different widths and three different positions of the slot. The second stage of this study is an investigation of an addition of a set of vanes in the annular cavity of the shroud bleed slot system. This investigation was performed using both CFD modelling and experimental measurements. The CFD model used a full stage steady state approach. Very good agreement was achieved between the experimental measurements of efficiency, pressure ratio and mass flow rate and those values predicted by the CFD model over the entire performance map, providing confidence in the CFD model as a tool to help understand the flow features of the bleed slot, its various geometries and an addition of annular cavity vanes. The first stage of the study emphasises the significance of the inclusion of a shroud bleed slot into the conventional turbocharger compressor stage and the appropriate choice of the slot geometry in order to achieve as the widest map possible. In comparison with the non-bleed slot compressor stage, the bleed slot significantly extended the map width at the higher speeds, by reducing the surge mass flow rate. However, no or very little improvement was found at lower speeds. The analysis of changes to design parameters revealed that it is vital to obtain an optimised geometry of the bleed slot system for a compressor stage to achieve a wider map without compromising other performance characteristics of the compressor. This study also discloses the importance of an optimised shape of the shroud bleed slot system to increase the compressor performance by avoiding the recirculation losses within the slot and cavity passages at both choke and surge flow conditions. In the second stage of the work presented in this thesis, three different types of the annular cavity vane (straight, positive curved and negative curved vanes) have been designed and investigated. The purpose of the annular cavity vane technique is to remove some of the positive swirl that can be carried through the bleed slot system, which would influence the pressure ratio. In addition to this, the series of cavity vanes provides better guidance to the slot recirculating flow before it mixes with the impeller main inlet flow. Better guidance of the flow improves the mixing at the inducer inlet in the circumferential direction. As a consequence, the stability of the compressor is improved at lower flow rates and a wider map can be achieved. The impact of these three cavity vane designs on the map width and performance of the compressor has been highlighted through a detailed analysis of the impeller and cavity vane bleed slot flow field. Interestingly, all three types of cavity vane showed an improvement in map width by moving the surge point to a lower mass flow rate with no significant efficiency penalty over the entire operating range. This improvement was most evident at the highest running speed. In particular, the negative curved vane showed a significant increase in map width which represents an extra 67% improvement in map width that was achieved between the baseline bleed slot and non-bleed slot configurations.

This thesis is concerned with a theoretical investigation into the nonlinear dynamic behaviour of a turbocharger. Specifically the instabilities due to oil-whirl are examined. These are self-excited vibrations existing in the form of an in-phase whirl mode and a conical whirl mode. Waterfall plots were provided by Cummins Turbo-Technologies Ltd., Huddersfield, UK, based on test data using two different unbalance levels on a turbocharger. The test with the high unbalance indicated that there was shift in the sub-synchronous frequency to synchronous frequency between about 80,000 rpm to 130,000 rpm. The literature suggests that this self-excited vibration can be suppressed using forced excitation. Moreover, it is well known that the existence of limit cycles enables successful operation of a turbocharger. This limit cycle is a periodic motion attributed to the nonlinearity of the oil-film, other than the stable and the unstable equilibrium states predicted by the linear analysis. Hence, a nonlinear analysis is required to analyse the limit cycle and to determine the effect of synchronous excitation on it. In the literature a variety of parameters has been shown to influence the dynamic behaviour of a rotor-bearing system. To avoid over-complicated mathematical modeling, the influence of two such parameters: gyroscopic moment and shaft flexibility are first investigated in this thesis using linear stability theory to determine their significance. Effects of gyroscopic action are investigated using symmetric and asymmetric rigid rotors supported on short journal bearings with full-film using rigid and damped supports. In this thesis, the damper supported journal bearing is used to simulate the floating ring bearings that are commonly used in automotive turbochargers. The outer film of the floating ring bearing is treated as an external damper, since the ring is assumed not to rotate but only wobble giving the damping effect from the squeezing action. A gyroscopic coefficient, which is defined as the ratio of the polar to the transverse moment of inertia of the rotor, is introduced. The threshold value of this coefficient is determined to be 1 for the suppression of the conical whirl instability. The stability of the in-phase whirl mode is unaffected by this parameter. A flexible rotor mounted in floating ring bearings with full-film, is analysed to confirm that it behaves as a rigid body up to a speed of 100,000 rpm. Prior to the unbalance response study, a perfectly balanced rigid rotor supported by rigidly supported bearings is first analysed to determine the nonlinear behaviour of the in-phase whirl. To include the stiffness-like radial restoring force, an oscillating 2 π -film cavitation model for the hydrodynamic bearings is used. The effect of a static load on the rotor is analysed to determine the nonlinear behaviour for a wide range of steady-state eccentricity ratios. A parameter plane separating the region of instability from that of stability is presented using linear analysis to determine the stability threshold at which the oil-whirl is initiated. The onset of oil-whirl phenomenon is shown to be the Hopf bifurcation. Particular emphasis is placed on examining the limit cycles (periodic oscillations) around the stability threshold. Reducing the nonlinear equation of motion to Poincare normal form, the first Lyapunov coefficients are evaluated to show the change in the type of bifurcation from sub-critical bifurcation (disappearance of an unstable limit cycle) to super-critical bifurcation (appearance of a stable limit cycle) around the stability threshold. Such bifurcations are demonstrated through plots of orbits using numerical integration by the Runge-Kutta method. With some unbalance added to the rotor-system, waterfall plots are generated to simulate the response characteristics observed in the test data, by running-up the speed. After the Centre Manifold reduction, the equations of motions are averaged for analysis. Using a numerical and an analytical procedure, it is shown that the unbalance is more effective in the transient motion than in the steady-state condition. Unbalance introduces a reduction in the growth rate of whirl amplitude upto a certain optimum unbalance value, above which the effect is reversed. The mechanism behind this behaviour is shown to be the shift in phase caused by the unbalance at the start of whirling, when the dynamic forces are comparable with the unbalance force. This is due to the coupling effect of amplitude and phase in an unbalanced rotor system

The present work advances progress on the validation against measurements of linear and nonlinear rotordynamic models for predicting the dynamic shaft response of automotive turbochargers (TCs) supported on floating ring bearings. Waterfall spectra of measured shaft motions at the compressor and turbine ends of a test TC rotor evidences a complex response, showing synchronous (1X) and multiple subsynchronous frequencies along the entire operating speed range (maximum shaft speed ~ 65 krpm). Postprocessing of the raw test data by mathematical software allows filtering the synchronous and subsynchronous vibration components for later comparisons to predicted shaft motions. The static performance of the floating ring bearings is analyzed with in-house software (XLSFRBThermal®), which considers thermal expansion of the shaft and bearing components as well as static loading on the bearing due to lubricant feed pressure. In addition, the program calculates rotordynamic force coefficients for the inner and outer films of the floating ring bearing. The turbocharger Finite Element (FE) structural model for the linear and nonlinear analyses includes lumped masses for the compressor and turbine wheels and the thrust collar. The mass imbalance distribution on the TC rotor is estimated from the test data using a procedure derived from the two-plane balancing method with influence coefficients. The linear model yields predictions of rotor synchronous (1X) response to imbalance and damped eigenvalues. The analysis evidences that the rotor cylindrical-bending mode is unstable at all shaft speeds while the rotor conical model becomes more unstable as lubricant feed pressure decreases. The predicted synchronous (1X) motions agree well with the test data, showing a critical speed at approximately 20 krpm. The linear stability results indicate the existence of three critical speeds occurring at 4, 20 and 50 krpm. The second critical speed corresponds to the rotor cylindrical-bending mode, showing larger amplitudes of motion at the compressor nose than at the turbine end. The third critical speed associated to the rotor first bending modes is well damped. In the nonlinear transient analysis, the nonlinear equations of motion of the system (rotor-FRB) are integrated, and the bearing reaction forces are calculated at each time step in a numerical integration procedure. The model then yields predictions of total motion which is decomposed into synchronous (1X) and subsynchronous motions, amplitudes and frequencies. The nonlinear analysis predicts synchronous (1X) amplitudes that correlate well with the test data at high shaft speeds (> 30 krpm) but underpredicts the imbalance response at low shaft speeds (<30 krpm). The time transient simulations predict multiple frequency subsynchronous motions for shaft speeds ranging from 10 krpm to 55 krpm, with amplitudes and frequencies that are in good agreement with the measurements. Finally, the shaft motion measurements and predictions demonstrate that the turbocharger dynamic response does not depend greatly on the lubricant feed pressure and inlet temperature for the conditions tested.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (leaf 24).
The turbocharger gas turbine engine was designed with the intent of being built as a demonstration for the Massachusetts Institute of Technology Department of Mechanical Engineering courses 2.005 and 2.006 to supplement material covered. A gas turbine operates on an open version of the Brayton cycle and consists of a compressor, a combustion chamber and a turbine. An automobile turbocharger was chosen because it contains a compressor and turbine on a common shaft. Designs for the combustion chamber, oil system, fuel system, and ignition system were created based on research of similar projects. Many of the necessary parts were also specified.
by Keane T. Nishimoto.
S.B.

Designers of engines have always looked for ways to improve the power to weight ratio of mobile internal combustion engines. This was especially true in aircraft engine design and engines for various forms of racing. Today designers are looking for ways to make everything from cars to road tractors to farm tractors lighter and thereby more efficient. In addition, in many cases these vehicles only need the maximum power that an engine can produce for a small amount of time. What is needed is a small, lightweight engine with the ability to produce a large amount of power for a short duration. The work here describes one possible method for constructing just such a type of engine. By adding a combustion chamber in the exhaust flow between the engine exhaust valve and the turbine inlet on a turbocharged diesel engine, it should be possible to increase the turbine temperature. This will in turn allow the turbine to deliver more power to the compressor and create a higher inlet pressure and allow the engine to create more power. This paper describes both a computer simulation and an engine with this combustion chamber installed. There were however, problems with both the simulation as well as the test engine. While no quantitative data was obtained from the test engine, some valuable observations were made. The computer simulation yielded results and from these results and observations made while testing the engine with the combustion chamber installed it was determined that this design shows promise of creating an engine with higher specific power.
Master of Science

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.
Includes bibliographical references.
As portable electronic devices proliferate (laptops, GPS, radios etc.), the demand for compact energy sources to power them increases. Primary (non-rechargeable) batteries now provide energy densities upwards of 180 W-hr/kg, secondary (rechargeable) batteries offer about 1/2 that level. Hydrocarbon fuels have a chemical energy density of 13,000-14,000 W-hr/kg. A power source using hydrocarbon fuels with an electric power conversion efficiency of order 10% would be revolutionary. This promise has driven the development of the MIT micro gas turbine generator concept. The first engine design measures 23 x 23 x 0.3 mm and is fabricated from single crystal silicon using MEMS micro-fabrication techniques so as to offer the promise of low cost in large production. This thesis describes the development and testing of a MEMS turbocharger. This is a version of a simple cycle, single spool gas turbine engine with compressor and turbine flow paths separated for diagnostic purposes, intended for turbomachinery and rotordynamic development. The turbocharger design described herein was evolved from an earlier, unsuccessful design (Protz 2000) to satisfy rotordynamic and fabrication constraints. The turbochargers consist of a back-to-back centrifugal compressor and radial inflow turbine supported on gas bearings with a design rotating speed of 1.2 Mrpm. This design speed is many times the natural frequency of the radial bearing system. Primarily due to the exacting requirements of the micron scale bearings, these devices have proven very difficult to manufacture to design, with only six near specification units produced over the course of three years. Six proved to be a small number for this development program since these silicon devices are brittle
(cont.) and do not survive bearing crashes at speeds much above a few tens of thousands of rpm. The primary focus of this thesis has been the theoretical and empirical determination of strategies for the starting and acceleration of the turbocharger and engine and evolution of the design to that end. Experiments identified phenomena governing rotordynamics, which were compared to model predictions. During these tests, the turbocharger reached 40% design speed (480,000 rpm). Rotordynamics were the limiting factor. The turbomachinery performance was characterized during these experiments. At 40% design speed, the compressor developed a pressure ratio of 1.21 at a flow rate of 0.13 g/s, values in agreement with CFD predictions. At this operating point the turbine pressure ratio was 1.7 with a flow rate of 0.26 g/s resulting in an overall spool efficiency of 19%. To assess ignition strategies for the gas turbine, a lumped parameter model was developed to examine the transient behavior of the engine as dictated by the turbomachinery fluid mechanics, heat transfer, structural deformations from centrifugal and thermal loading and rotordynamics. The model shows that transients are dominated by three time constants - rotor inertial (10⁻¹ sec), rotor thermal (lsec), and static structure thermal (10sec). The model suggests that the engine requires modified bearing dimensions relative to the turbocharger and that it might be necessary to pre-heat the structure prior to ignition ...
by Nicholas Savoulides.
Ph.D.

Simulation tools are intensively used in the design stage of diesel engines due to their contributions to significant savings in cost and time for the engine development. Since most of DI diesel engines are turbocharged, it is of vital importance to hold a good understanding of turbine and compressor characteristic to predict the engine performance accurately. However, this data is often not available from turbocharger manufacturers, particularly for turbines. On available turbine maps the operating range of the turbine is constrained due to limitations of conventional turbocharger test benches. Operations with a wider range of turbocharger pressure ratios can be achieved by employing complex turbocharger test benches, which will also lead to higher costs including hardware and labour. An alternative solution is to develop numerical models for the turbocharger based on thermodynamics. In this thesis numerical models has been developed for predicting the performance of both the centrifugal compressors and turbines and they have been also validated using test cases, particularly for variable geometry turbines. Following detailed parametric studies, the turbocharger model has been validated against experimental data of a turbocharger with a variable geometry turbine. Results showed that the model was capable of predicting the characteristics maps of the turbocharger accurately, requiring a minimal amount of turbocharger geometric properties, experimental data and calibration parameters. Thus, by combing with the engine performance simulation software there is a highly potential for the numerical model developed in this work to become a useful tool for predicting engine performance and turbo matching calculations or diagnostic applications.

Data-driven predictive vehicle maintenance can in principle reduce the risk of costly breakdowns, damaged cargo, and increased emissions due to faulty components. However, implementing a cost efficient predictive maintenance policy is far from trivial. This thesis presents a machine learning-based method for predicting turbocharger component failure in heavy-duty trucks, called Survival-PLSTM. Survival-PLSTM uses a recurrent neural-network to model time-series data of a vehicle’s operational history, and outputs an approximated cumulative hazard function. The method addresses a number of challenges related to modeling vehicle component failures, including right- censored data, class imbalance and uninformative features. The maintenance policy generated by Survival-PLSTM is shown to be more cost efficient than a corrective maintenance policy under feasible conditions. When predicting failure within a given time period as a binary outcome, Survival- PLSTM compares favorably with the Random Survival Forest (RSF) model ≤ ≤ false positive cost — previously proposed for similar applications — in terms of sensitivity and specificity. The cost efficiency of a model-generated maintenance policy is shown to depend on the ratio between false-negative cost and false-positive cost, β := false negative cost . Survival-PLSTM generates a more cost efficient policy when β > 3.5, while RSF is superior when 1 β 3.5. Both models produce more cost efficient maintenance policies than a corrective maintenance policy.
Datadrivet prediktivt underhåll av fordon kan potentiellt minska riskerna för kostsamma fordonsstopp, skadad last, samt ökade utsläpp till följd av felande komponenter. Att generera prediktiva underhållsplaner med datadrivna metoder som också är kostnadseffektiva är dock inte enkelt. Detta examensarbete presenterar en metod för prediktion av turboladdarfel i lastbilar. Metoden kombinerar tillämpad maskininlärning med teori från det statistiska området överlevnadsanalys, och har fått namnet Survival- PLSTM. Survival-PLSTM använder ett Recurrent Neural Network (RNN) för att modellera tidsseriedata insamlad från lastbilar i drift. Givet en lastbils insamlade data producerar Survival-PLSTM en uppskattad diskret kumulativ fördelningsfunktion som uttrycker sannolikhet för turbofel över tid. Metoden tar hänsyn till flera utmaningar relaterade till modellering av komponentfel i lastbilar, såsom högercensurerad data, klassimbalans och icke-informativa variabler. Underhållsplanen som Survival-PLSTM genererar visas vara mer kostnadseffektiv än en avhjälpande underhållsplan (corrective maintenance), under rimliga förhållanden. Survival-PLSTM kan användas för att prediktera turboladdarfel som ett binärt utfall inom ett givet tidsfönster. På denna uppgift har Survival-PLSTM jämförbar sensitivitet och specificitet som Random Survival Forest (RSF), vilket är en datadriven metod som tidigare använts i liknande syfte. Kostnadseffektiviteten av en modellgenererad underhållsplan visas bero på kvoten mellan kostnaden för falsk-negativa respektive falsk- positiva prediktioner, β := falsk-negativ kostnad . Survival-PLSTM visas producera en kostnadseffektivare underhållsplan när β > 3.5, medan RSF visas vara bättre då 1 β 3.5. Båda modellerna producerar underhållsplaner som är mer kostnadseffektiva än en avhjälpande underhållsplan.

Turbochargers are becoming an essential device in internal combustion engines as they boost the intake air with more pressure in order to increase the power output. These devices are normally designed for a single steady design point but the pulsating flow delivered from the internal combustion engine is everything but steady. The efficiency drop experienced in the off-design points by the fixed geometry turbochargers have made some research groups to look into new variable geometry solutions for turbocharging. A nozzle ring is a device which normally achieves a higher performance under design conditions, but the efficiency rapidly drops at off-design conditions. In this paper, a variable angle nozzle ring is designed and implemented in the model of a radial turbine of a turbocharger in order to study its potential when working under real internal combustion engine cycles. To understand the profit margin the turbine performance is compared with two turbines with the same impeller geometry: one without nozzle ring and one with a nozzle ring with a fixed angle. The results show that the maximum efficiency angle function calculated for the variable angle nozzle ring achieves an improvement in the total efficiency of 5 % when comparing with a turbine with a fixed angle and 18 % when comparing with a vaneless turbine. The improved guidance achieved due to the variable blade angle leads to less turbine losses and therefore more mechanical energy can be extracted from the exhaust mass flow throughout all the combustion cycle but a further study should be made in order to match all the engine operations points. Notably, taking the pulsating boundary conditions into consideration, a remarkable improvement is achieved already for the fixed angle nozzle ring.

Methods of determining natural frequencies of the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs for various environmental conditions were investigated by application of Finite Element Analysis and beam theory. Modelling and simulation methods were developed ; the first method composed of 15 finite element simulations ; the second composed of 15 finite element simulations and a set of experimental frequency survey results; the third composed of 5 simulations , an incorporated mathematical model and a set of experimental frequency survey results. Each of these methods was designed to allow prediction of resonant frequency changes across a range of exhaust gas temperature and shaft rotational speed. For the new modelling and simulation methods, an analysis template and a plotting tool were developed using Microsoft Excel and MATLAB software. A graph showing a frequency-temperature-speed variations and a Campbell Diagram that incorporates material stiffening and softening effects across a range of rotational speeds was designed, and applied to the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs. New design methodologies for turbine wheels were formulated and validated, showing a good agreement with a range of data points from frequency survey, strain-gauge telemetry and laser tip-timing test results. The results from the new design method were compared with existing single compensation factor methodology, and showed a great improvement in accuracy of prediction of modal vibration. A new nomenclature for the mode shapes of a turbocharger’s blade was proposed, designed and demonstrated to allow direct identification of associated mode shape. It is concluded that Finite Element Analysis combined with the frequency survey is capable of predicting changes in turbine natural frequencies and, when incorporated into the existing turbine design methodology, resulted in a major improvement in the accuracy of the predictions of vibration frequency.

Turbocharging systems are of high importance in the enhancement of engine power and efficiency. Faults in such systems may cause increased emissions levels beyond those set by legislation, and may also compromise fuel efficiency. This thesis investigates the application of system identification and vibration signal analysis techniques for the performance monitoring of turbocharged diesel engines by exploring turbocharger behaviour. The first technique is based on the use of system identification to build models representing the input and output relationship of an engine process. In this case, torque demand is the input, and the turbocharger speed is the output in a medium duty, turbocharged diesel engine. The proposition set here is that the model that can be derived does not have to reflect the complexity of the physical system. Hence, if simple models can be derived, any deviation from the model of normal operation, if adhering to some principles, could indicate the existence of a fault in a system. Dynamic linear auto-regressive moving averages with exogenous input (ARMAX) models were estimated to represent the relationship between input and output. The models have been used to demonstrate the capability of the proposed technique to diagnose faults.

Master of Science
Department of Mechanical and Nuclear Engineering
Kirby S. Chapman
Continued regulatory pressure necessitates the use of precisely designed turbochargers to create the design trapped equivalence ratio within large-bore stationary engines used in the natural gas transmission industry. The upgraded turbochargers scavenge the exhaust gases from the cylinder, and create the air manifold pressure and back pressure on the engine necessary to achieve a specific trapped mass. This combination serves to achieve the emissions reduction required by regulatory agencies. Many engine owner/operators request that an upgraded turbocharger be tested and verified prior to re-installation on engine. Verification of the mechanical integrity and airflow performance prior to engine installation is necessary to prevent field hardware iterations. Confirming the as-built turbocharger design specification prior to transporting to the field can decrease downtime and installation costs. There are however, technical challenges to overcome for comparing test-cell data to field conditions. This thesis discusses the required corrections and testing methodology to verify turbocharger onsite performance from data collected in a precisely designed testing apparatus. As the litmus test of the testing system, test performance data is corrected to site conditions per the design air specification. Prior to field installation, the turbocharger is fitted with instrumentation to collect field operating data to authenticate the turbocharger testing system and correction methods. The correction method utilized herein is the ASME Performance Test Code 10 (PTC10) for Compressors and Exhausters version 1997.

This project was initiated to more fully understand the dynamic stability of an automotive turbocharger rotor-bearing system using both linear and nonlinear analyses. The capabilities of a commercial Finite Element Analysis (FEA) code (computer program) were implemented in the investigation process. Several different hydrodynamic journal bearings were employed in the study of the turbocharger linearized dynamic stability. The research demonstrates how the linear analysis of a turbocharger rotordynamics can be very beneficial for the design evaluation and maintenance purposes.
Master of Science

Rotor stability is essential to the life span of any piece of rotating machinery; it becomes increasingly critical in high-speed machinery such as turbochargers. Large turbochargers, such as those found in marine diesel propulsion engines where the rotor alone often exceeds forty pounds, require careful consideration regarding stability as well as load support during the bearing selection process. Logarithmic Decrement is the primary consideration for rotor stability. Commercial software is used to model and analyze a proven unstable turbocharger rotor. After confirming that the model exhibits unstable characteristics, the same turbocharger is then analyzed with various fluid-film bearing configurations. Finally, the tilting-pad bearing is determined to be the best bearing for this turbocharger application, stabilizing the rotor throughout the entire designed operating range.
Master of Science

Существующие методы и программы расчёта динамики роторов позволяют определить критические частоты и формы, а также вынужденные колебания синхронной прецессии. В то же время эти программы не могут быть использованы для расчёта и прогнозирования таких сложных явлений, как потеря устойчивости и появления несинхронных суб- и супергармонических составляющих. Эти явления могут быть изучены с помощью численного интегрирования нелинейных уравнений движения ротора. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/31812

Тенденция развития современных роторных машин связана с ростом их производительности и рабочих частот вращения и уменьшением габаритных размеров агрегатов, что вместе с необходимостью обеспечения длительного ресурса работы накладывает существенные ограничения на использование подшипников качения. В связи с этим широкое распространение в качестве опор роторов высокоскоростных турбомашин находят подшипники жидкостного трения. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/8045

Flow in a turbocharger turbine is highly unsteady in nature as it responds to the exhaust manifold of an internal combustion (IC) engine. Despite this it is conventional to use quasi-steady turbine models in one-dimensional turbocharged engine simulations, even though they cannot reproduce the known hysteresis of turbine mass flow and performance characteristics recorded under pulsating flow conditions. Using filling-and-emptying models improves the situation by permitting mass accumulation in the turbine volute. Depending on the unsteadiness level, this approach may still be insufficient to capture true turbine operation since neither method can resolve unsteady effects due to pressure wave action in the flow. It is unclear when transition occurs between filling-and- emptying and wave action modes. To this end, a proprietary computational gas dynamics code in C++ is presented to simulate the unsteady, compressible flow inherent to IC engine exhaust manifolds. The Euler equations for one-dimensional inviscid flow are discretized to provide second-order, conservative, shock-capturing finite difference schemes able to resolve wave propagation in ducts with area variation, wall friction and heat transfer. A wave action turbine volute model is constructed using bespoke boundary conditions. Validation against experimental data shows satisfactory agreement for pulse frequencies up to 40 Hz, and improved instantaneous swallowing capacity prediction at all tested frequencies compared to quasi-steady calculations. Fourier series characterization of on-engine pulse waveforms reveals multiple harmonic components, causing significant regions of divergence between filling-and-emptying and wave action predicted hystereses. Comparison of concurrent wave action and filling-and-emptying simulations applying simpler sinusoidal waveforms allows development of the unsteadiness measures FSt and FSt(p). An approximate guideline to ensure a filling-and-emptying mode stipulates FSt [Symbol appears here. To view, please open pdf attachment]0.15 and FSt(p) [Symbol appears here. To view, please open pdf attachment]0.02. Evaluation of FSt and FSt(p) for an example on-engine case indicates certain wave action already by 1600 rev/min, borne out by subsequent inspection of the swallowing capacity traces.

The vibration of a turbocharger blade and dynamic characteristics of bladed packets connected by a lacing wire have been studied. The study was carried out using three analytical and experimental methods. They are: Modal Testing, Electronic Speckle Pattern Interferometry (ESPD and Finite Element Analysis (FEA)). Vibration modes of a turbocharger blade with aerodynamic profile, with and without a lacing wire, were identified using model blades with simplified geometry. The separation of coupled modes was achieved using ESPI tests. The modes of vibrations of bladed packets were identified. The effect of inter-blade coupling through a lacing wire is that a cluster of sub-modes are generated in bladed packets corresponding to each fundamental mode of the freestanding blade, the number of the sub-modes being equal to the number of blades in the packet. Apart from the fundamental sub-mode, the vibration of all other submodes are out of phase with different phase relations. The stiffness of the lacing wire and its location with respect to the blade make great contributions towards certain mode clusters in terms of mode shapes and natural frequencies. The nonlinearity of the stiffness of the deformed lacing wire caused by centrifugal force was established. The coupling of this non linearity with different vibration amplitudes, due to different phase relation, results in the dynamic mistuning in lacing wire stiffness. This mistuning is considered to be a major attribute in reducing the responses at resonance.

This thesis investigates the impact of volute design on the performance of a mixed flow turbine. Both computational and experimental methods were used to assess performance. All computational work as conducted in CFX under both steady state and unsteady pulsating conditions with the models including inlet, volute, rotor and outlet volumes. Both the mixing plane and sliding mesh approaches were implemented and the results compared. The k-w SST turbulence model was implemented throughout this thesis with the exceptions of chapters 8 and 9 where the SAS SST model was used in an attempt to accurately capture secondary flows. Further SBES simulations were included for flow validation. It was found that pulse shape had a significant impact on the instantaneous performance while the cycle averaged performance remained largely insensitive to the changes. Further thorough analysis showed, under a range of pulse frequencies, loads and amplitudes, significant variations in LE incidence over the pulse cycle. Furthermore, the spanwise distribution of the incidence also changed considerably over the pulse due to volute secondary flow development. As result of the initial analysis both volute tilt and aspect ratio (and a combination of the two) were assessed. A new tilted volute was introduced which resulted in a performance improvement of up to 2.356% in cycle averaged rotor efficiency and 2.171% improvement in cycle average stage efficiency. This improvement reduced when volute A/r was reduced. The impact of volute aspect ratio showed that the MFP varied by up to 4.3%. Furthermore, volute secondary flows were significantly impacted by aspect ratio with smaller aspect ratios resulting in strong vortices that persisted around the volute. Increasing the aspect ratio removed these vortices. However, the span-wise distribution of LE incidence was only slightly improved with increasing aspect ratio. The maximum efficiency improvement measured over the aspect ratio range was 1.47% for the turbine stage. Combining both tilt and aspect ratio showed a maximum performance variation between the worst performing design, radial AR=0.5 and the best performing design tilted AR=2 of 3.00% in the rotor region and 2.87% over the entire stage. Extensive experimental testing under steady state and pulsating flows was conducted at Imperial College, London to validate the computational work. It was observed that the tilted volute resulted in pulsating efficiency improvements at 48krpm and 56krpm. This trend was found to increase as pulse frequency increased. However, steady state testing only showed efficiency improvements at 30krpm for the tilted volute.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 183-187).
This thesis presents an investigation of the effects of Ported Shroud (PS) self-recirculating casing treatment used in turbocharger centrifugal compressors for increasing the operable range. Computed results, assessed with experimental measurements on ported and non-ported variants of a representative turbocharger compressor, are used to determine the impact of the PS on the flow field and hence performance. It is shown that the main flow path perceives the PS flow as a combination of flow actuations that include injection and removal of mass flow, and injection of axial momentum and tangential momentum. A computational model in which the presence of the PS is replaced by imposed boundary conditions that reflect the individual flow actuations has thus been formulated and implemented. The removal of a fraction of the inducer mass flow was determined to be the dominant flow actuation in setting the performance of PS compressors. Mass flow removal reduces the flow blockage associated with the impeller tip leakage flow and increases the diffusion in the main flow path. Adding swirl to the injected flow in the direction opposite of the wheel rotation results in an increase of the stagnation pressure ratio and a decrease of the efficiency. The loss generation in the flow path has been defined to rationalize efficiency changes associated with PS operation.
by George Alexander Christou.
Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
DISCLAIMER NOTICE: The pagination in this thesis reflects how it was delivered to the Institute Archives and Special Collections, Massachusetts Institute of Technology. Cataloged from PDF version of thesis.
Includes bibliographical references.
An experimental study on the effects of after treatments and a turbocharger on emissions of a single cylinder diesel engine. The study measured the concentration of CO, CO2, HC, NO, NO2, and NOx. Tests on the engine were performed at different engine loads and engine speeds. The engine power ranged from 0 to 9 HP, and the engine speed ranged from 1500 to 3500 rpm. Emissions were characterized in terms of engine speed, engine power, and exhaust temperature. The results showed that the optimal strategy for emission reduction was to combine the Diesel Oxidation Catalyst and the Diesel Particulate Filter to form a Continuously Regenerating Trap. These after treatments would be combined with the use of a turbocharger and air capacitor to ensure that the back pressure doesn't take away too much power and increase fuel consumption.
by Kristina Schmidt.
S.B.

Orientador: Milton Dias Júnior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-25T09:48:12Z (GMT). No. of bitstreams: 1 Nomura_PaulaWatanabe_M.pdf: 4842075 bytes, checksum: fb2b3e20baadde947cb7b9aad16227d8 (MD5) Previous issue date: 2014
Resumo: As novas legislações de emissões demandam das montadoras de veículos automotores, o desenvolvimento de tecnologias para melhorar o consumo de combustível e emissão de poluentes. Seguindo esta tendência, os sistemas de turbocompressores inovam junto e lançam ao mercado novas arquiteturas de turbos. Uma delas é o turbocompressor regulado de dois estágios, que otimiza a eficiência em um intervalo de rotação mais amplo. Neste sistema, há dois turbocompressores: o estágio de baixa pressão e de alta pressão. O primeiro tem maior influência nas baixas rotações, enquanto o segundo nas altas rotações do motor. Entre os dois estágios, existe uma válvula bypass que controla a passagem do gás de escape para o estágio de baixa pressão, evitando assim, sobrecarregar o estágio de alta pressão. Esta válvula bypass é composta por um eixo rotativo e uma bucha fixa, e exatamente entre estes dois componentes foi detectado desgaste, aumentando as folgas e causando vazamento de gás. Com o objetivo de diminuir este vazamento e resolver o problema, uma investigação sobre este desgaste prematuro foi iniciada dentro da empresa onde a autora da presente dissertação trabalha. Neste trabalho a análise de forças das condições estática e dinâmica que envolve a bucha e o eixo, as forças e momentos para abrir e fechar o prato da válvula, e as equações de movimento são apresentadas. A análise experimental inclui medições feitas em dois motores reais: um deles conectado a um dinamômetro e o outro instalado em um veículo usado na mesma aplicação onde o desgaste excessivo foi observado. Além disso, a análise de desgaste de dez pares bucha-eixo que retornaram de testes de durabilidade é apresentado. A comparação do desgaste entre dois sistemas de bucha e eixo foi realizada. Ambos os sistemas rodaram na mesma condição, exceto pela frequência de operação da válvula de controle, assim a influência desta frequência pôde ser analisada. Ao final, todo este dado foi coletado e usado para o cálculo de taxa de desgaste que avalia a influência de diferentes parâmetros de design sobre a taxa de desgaste
Abstract: The new emission legislations demand, from vehicle manufactures the development of technologies to improve fuel consumption and pollutants emission. Following this trend, the turbocharging systems innovate together and release new turbocharger architectures in the market. One of them is the regulated-two-stages turbocharger, which optimizes the efficiency in a broader engine speed range. In this system, there are two turbochargers, the high and low pressure stages. The former has a bigger influence on the low engine speeds, and the latter in the higher engine speeds. Between both stages there is a bypass valve that controls the gas flow to the low pressure stage, avoiding overpressure in the high pressure stage. This bypass valve is composed by a rotating shaft and a fixed bushing, and exactly between these two components it was detected wear, increasing the clearances and causing gas leakage. In order to reduce this leakage and solve the problem, an investigation about this premature wear has started inside the company where the author of the present dissertation works. In the present work the force analysis of the static and dynamic conditions that involve the shaft and bushing, the forces and momentum to open and close the valve plate, and the equations of motion are presented. The experimental analysis includes measurements made on two real engines: one of them connected to a dynamometer and the other installed on a vehicle used on the same application where the excessive wear was observed. Also, the wear analysis of ten shafts and bushings returned from durability tests is presented. The wear comparison between two shaft-bushing systems was performed. Both systems run in the same condition except for the control valve operational frequency, so the influence of this frequency could be evaluated. In the end, this entire data base collected could be used as input to a wear rate calculation that evaluates the influence of different design parameters on the wear rate
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestra em Engenharia Mecânica

Rotors in fluid-film bearing supported turbomachinery are known to develop elliptical orbits as a result of rotor-bearing interactions, mass unbalance within the rotor, gravitational bending of the shaft and external excitation. In synchronous whirl, where the speed at which the shaft travels about the orbit is equal to the rotational speed of the rotor, temperature gradients may develop across the journal as a result of viscous shear in the bearingâ s lubricant film. This thermal gradient leads to bending of the shaft in a phenomenon known as The Morton Effect. Such thermally induced bending causes further growth of the elliptical orbit resulting in further bending leading to excessive vibration levels and premature bearing failure. This analysis examines the development of the Morton Effect in medium-speed turbochargers typical to shipboard propulsion engines and the effect that bearing clearance has on thermal stability. Floating ring and tilting pad journal bearings are considered with a single stage, overhung centrifugal compressor and an overhung axial turbine. Results indicate a correlation between bearing clearance and thermal stability in the rotor-bearing system. A model for the aerodynamic force generated as a result of interaction between air exiting a centrifugal compressor and the compressorâ s annulus in a turbocharger is then developed and applied to the rotor-bearing systems. Results suggest little correlation between this aerodynamic force and the development of the Morton Effect.
Master of Science

Rotordynamic instability is present in most or all automotive turbochargers. High subsynchronous amplitudes can cause a variety of problems in areas such as mechanical failures, emissions regulations and rotor design. Self-excited vibrations from sources of damping can lock in at lateral natural frequencies causing dangerously high vibration levels. The resulting high-amplitude conical and bending modes can be reduced in order to achieve a more robust system. This research focuses on the relationship between synchronous and subsynchronous amplitude levels. It is theorized that an increase in unbalance could cause a reduction in subsynchronous vibration amplitudes. Through the use of a custom turbocharger, a series of unbalances were applied to both the turbine and compressor wheels and the resulting amplitudes were recorded off a modified compressor nut. The resulting data were reduced and are presented at the end of this paper.
Master of Science

Automotive turbochargers experience self-excited instabilities through the majority of their operating speed range. The results of these instabilities can cause damage to the bearings, shafts, and housing walls. Preventing this damage while maintaining or increasing performance characteristics is a huge concern to industry due to the time and money needed to replace vital components. The aim of this research is to determine which characteristics of the bearings have the greatest influence on the damped natural frequencies. It was believed that axial groove bearings could offer an acceptable alternative to the floating ring bearings currently found in automotive turbochargers. DyRoBeS rotor dynamics software was used to determine analytically damped natural frequencies for floating ring bearings, and also for six, eight, and ten axial groove fixed geometry bearings, under different speed and loading conditions. The resulting data were compared to experimental test results from an on-engine turbocharger test stand and presented in this report.
Master of Science