Yes / A laser induced fluorescence system has been developed to visualise the oil film thickness between the piston ring and cylinder wall of a fired gasoline engine via a small optical window mounted in the cylinder wall. A fluorescent dye was added to the lubricant in the sump to allow the lubricant to fluoresce when absorbing laser radiation. The concentration of the dye did not disturb the lubricant chemistry or its performance. Degraded engine oil samples were used to investigate the influence of lubricant quality on ring pack lubricant film thickness measurements. The results show significant differences in the lubricant film thickness profiles for the ring pack when the lubricant degrades which will affect ring pack friction and ultimately fuel economy.

In response to the global concerns towards oil scarcity and climate change, the automotive industry is currently focusing on improving fuel economy and reducing exhaust emissions. Modern downsized gasoline engines that come with a package that includes a boosting system, variable valve train and direct fuel injection system is effective for fuel economy improvement and emission reduction. However, the knocking issue becomes severe at high load operations as a result of the high intake boosting pressure. In regard to the part load conditions, the gas exchange process requires extra work to draw in air into the cylinder due to a lower amount of pressure in the intake manifold caused by the restriction of the throttle plate. The Miller cycle is regarded as a potential strategy of knock control for downsized gasoline engines. Extensive works have sought to examine the performance improvement via the Miller cycle, yet only limited research has been conducted on the manner in which it can influence knock suppression. The focus of this thesis is to investigate early and late intake valve closing timings in terms of how they affect the compression process, the ability to suppress engine knock and meet the power output required at high loads for spark-ignited gasoline engines. Apart from that, this research also demonstrates the Miller cycle potential by utilising fully variable valve timing in controlling the load at the part load condition without using a throttle. The early intake valve closing with different valve lifts was tested in order to investigate the impact during the gas exchange process, particularly the pumping losses and the potential to improve fuel economy. This study includes both experimental and simulation studies. A Lotus single-cylinder research engine referred to as SCORE was mainly used for the experimental component of the study. The simulation work was conducted using a one-dimensional spark ignition engine model built in the Ricardo WAVE software for naturally-aspirated and downsized engines. The engine model values are validated against the experimental values from the Lotus SCORE and Lotus SABRE engines. The combustion model with a reduced kinetics mechanism was validated using a Rover K-series engine. A broad matrix of the engine operations has been investigated combining a variety of engine speeds and engine loads. The Miller cycle effects on knock suppression in a downsized engine environment have been investigated in three parts, namely the Miller cycle at different speed-load, knock suppression with extreme Miller cycle, and knock analysis with combustion kinetics. Through the works, the Miller cycle has demonstrated its capability to suppress engine knocking in a more efficient manner as opposed to the standard engine operation. This is contributed by the fact that early and late intake valve closings could affect the end gas condition at the end of the compression stroke, thus making it possible to suppress the engine knocking. The experimental study for controlling load without using throttle under the naturally-aspirated condition found that the Miller cycle with an early intake calve closing strategy able to improve fuel consumption by reducing pumping losses. The downsized engine condition, which has been evaluated via modelling work, also showed an improved performance trend using the unthrottled Miller cycle strategy. The open cycle and close cycle efficiencies have improved through the Miller cycle implementation. The contribution of this work is made in order to establish the comparison of the Miller cycle strategy in suppressing knocking between the early intake valve closing and late intake valve closing under a boosted environment. For the part load condition of the downsized engine, the research contributes to the existing body of knowledge by comparing the throttle-less Miller cycle and the standard throttled operation as a load control strategy.

Controlled Auto-Ignition (CAI) also known as Homogeneous Charge Compression Ignition (HCCI) is increasingly seen as a very effective way of lowering both fuel consumption and emissions. Hence, it is regarded as one of the best ways to meet stringent future emissions legislation. It has however, still many problems to overcome, such as limited operating range. This combustion concept was achieved in a production type, 4-cylinder gasoline engine, in two separated tests: naturally aspirated and turbocharged. Very few modifications to the original engine were needed. These consisted basically of a new set of camshafts for the naturally aspirated test and new camshafts plus turbocharger for the boosted test. The first part of investigation shows that naturally aspirated CAI could be readily achieved from 1000 to 3500rpm. The load range, however, decreased noticeably with engine speed due to flow restrictions imposed by the low lift camshafts. Ultra-low levels of NOx emissions and reduced fuel consumption were observed. After baseline experiments with naturally aspirated operation, the capability of turbocharging for extended CAI operation was investigated. The results show that the CAI range could achieve higher load and speed with the addition of the turbocharger. The engine showed increased fuel consumption due to excessive pumping losses. Emissions, however, have been reduced substantially in comparison to the original engine. NOx levels could be reduced by up to 98% when compared to a standard SI production engine.

Particulate number (PN) standards in current and future emissions legislation pose a challenge for designers and calibrators during the warm-up phases of cold direct injection spark ignition (DISI) engines. To achieve catalyst light-off conditions in the shortest time, engine strategies are often employed that inherently use more fuel to attain higher exhaust temperatures. These can lead to the generation of locally fuel-rich regions within the combustion chamber and hence the formation and emission of particulates. To meet these emissions requirements, further understanding of the DISI in-cylinder processes during cold-start are required. This thesis investigates the effect of cooling an optical research engine to temperatures as low as -7°C, one of the legislative test conditions. A high-speed 9 kHz optical investigation of the in-cylinder combustion and fuel spray along with in-cylinder pressure measurements was completed with the engine motored and fired at 1500 rpm during combustion conditions that were essentially homogeneous and stoichiometric. Results showed significant differences between the flame growth structures at various operating temperature conditions with the notable presence of fuel-rich regions, which are understood to be prominent areas of particulate formation. Measured engine performance parameters such as indicated mean effective pressure (IMEP) and mass fraction burned (MFB) times correlated with the observed differences in combustion characteristics and flame growth speed. It was shown that flash boiling of the fuel spray was present in the fully heated engine case and significantly reduced the penetration of the spray plume and the likelihood of piston crown and cylinder liner impingement. The flow and combustion processes of a transient production cold start-up strategy were analysed using high-speed particle image velocimetry (HSPIV). Results highlighted a broad range of flame structures and contrasting flame stoichiometry occurring at different times in the start-up process. Turbulent flow structures were identified that have an effect on the fuel spray development and combustion process as well as providing a path for cold-start emissions reduction. PN and transient hydrocarbon (HC) emissions were measured at cold conditions to further elucidate the effect of operating temperature and correlate emissions data with in-cylinder measurements. A clear link between the quantity and size range of particulate and HC emissions and operating temperature was shown and the precise in-cylinder location of HC emissions, caused by fuel impingement, was inferred from the HC emissions data.

Regulations for ICE-based transportation in the EU seek carbon dioxide emissions lower than 95 g CO2/km by 2020. In order to fulfill these limits, improvements in vehicle fuel consumption have to be achieved. One of the main losses of ICEs happens in the exhaust line. Internal combustion engines transform chemical energy into mechanical energy through combustion; however, only about 15-32% of this energy is effectively used to produce work, while most of the fuel energy is wasted through exhaust gases and coolant. Therefore, these sources can be exploited to improve the overall efficiency of the engine. Between these sources, exhaust gases show the largest potential of Waste Heat Recovery (WHR) due to its high level of exergy. Regarding WHR technologies, Rankine cycles are considered as the most promising candidates for improving Internal Combustion Engines. However, the implementation of this technology in modern passenger cars requires additional features to achieve a compact integration and controllability in the engine. While industrial applications typically operates in steady state operating points, there is a huge challenge taking into account its impact in the engine during typical daily driving profiles. This thesis contributes to the knowledge and characterization of an Organic Rankine Cycle coupled with an Internal Combustion Engine using ethanol as working fluid and a swash-plate expander as expansion machine. The main objective of this research work is to obtain and quantify the potential of Organic Rankine Cycles for the use of residual energy in automotive engines. To do this, an experimental ORC test bench was designed and built at CMT (Polytechnic University of Valencia), which can be coupled to different types of automotive combustion engines. Using these results, an estimation of the main variables of the cycle was obtained both in stationary and transient operating points. A potential of increasing ICE mechanical efficiency up to 3.7% could be reached at points of high load installing an ORC in a conventional turbocharged gasoline engine. Regarding transient conditions, a slightly simple and robust control based on adaptive PIDs, allows the control of the ORC in realistic driving profiles. High loads and hot conditions should be the starting ideal conditions to test and validate the control of the ORC in order to achieve high exhaust temperatures that justify the feasibility of the system. In order to deepen in the viability and characteristics of this particular application, some theoretical studies were done. A 1D model was developed using LMS Imagine.Lab Amesim platform. A potential improvement of 2.5% in fuel conversion efficiency was obtained at the high operating points as a direct consequence of the 23.5 g/kWh reduction in bsfc. To conclude, a thermo-economic study was developed taking into account the main elements of the installation costs and a minimum Specific Investment Cost value of 2030 €/kW was obtained. Moreover, an exergetic study showed that a total amount of 3.75 kW, 36.5% of exergy destruction rate, could be lowered in the forthcoming years, taking account the maximum efficiencies considering technical restrictions of the cycle components. / Las normativas anticontaminantes para el transporte propulsado por motores de combustión interna alternativos en la Unión Europea muestran límites de emisión menores a 95 g CO2/km para el año 2020. Con el fin de cumplir estos límites, deberán ser realizadas mejoras en el consumo de combustible en los vehículos. Una de las principales pérdidas en los Motores de Combustión Interna Alternativos (MCIA) ocurre en la línea de escape. Los MCIA transforman la energía química en energía mecánica a través de la combustión; sin embargo, únicamente el 15-32% de esta energía es eficazmente usada para producir trabajo, mientras que la mayor parte es desperdiciada a través de los gases de escape y el agua de refrigeración del motor. Por ello, estas fuentes de energía pueden ser utilizadas para mejorar la eficiencia global del vehículo. De estas fuentes, los gases de escape muestran un potencial mayor de recuperación de energía residual debido a su mayor contenido exergético. De todos los tipos de Sistemas de Recuperación de Energía Residual, los Ciclos Rankine son considerados como los candidatos más prometedores para mejorar la eficiencia de los MCIA. Sin embargo, la implementación de esta tecnología en los vehículos de pasajeros modernos requiere nuevas características para conseguir una integración compacta y una buena controlabilidad del motor. Mientras que las aplicaciones industriales normalmente operan en puntos de operación estacionarios, en el caso de los vehículos con MCIA existen importantes retos teniendo en cuenta su impacto en el modo de conducción cotidianos. Esta Tesis contribuye al conocimiento y caracterización de un Ciclo Rankine Orgánico acoplado con un Motor de Combustión Interna Alternativo utilizando etanol como fluido de trabajo y un expansor tipo Swash-plate como máquina expansora. El principal objetivo de este trabajo de investigación es obtener y cuantificar el potencial de los Ciclos Rankine Orgánicos (ORC) para la recuperación de la energía residual en motores de automoción. Para ello, una instalación experimental con un Ciclo Rankine Orgánico fue diseñada y construida en el Instituto Universitario "CMT - Motores Térmicos" (Universidad Politécnica de Valencia), que puede ser acoplada a diferentes tipos de motores de combustión interna alternativos. Usando esta instalación, una estimación de las principales variables del ciclo fue obtenida tanto en puntos estacionarios como en transitorios. Un potencial de mejora en torno a un 3.7 % puede ser alcanzada en puntos de alta carga instalando un ORC en un motor gasolina turboalimentado. Respecto a las condiciones transitorias, un control sencillo y robusto basado en PIDs adaptativos permite el control del ORC en perfiles de conducción reales. Las condiciones ideales para testear y validar el control del ORC son alta carga en el motor comenzando con el motor en caliente para conseguir altas temperaturas en el escape que justifiquen la viabilidad de estos ciclos. Para tratar de profundizar en la viabilidad y características de esta aplicación particular, diversos estudios teóricos fueron realizados. Un modelo 1D fue desarrollado usando el software LMS Imagine.Lab Amesim. Un potencial de mejora en torno a un 2.5% en el rendimiento efectivo del motor fue obtenido en condiciones transitorias en los puntos de alta carga como una consecuencia directa de la reducción de 23.5 g/kWh del consumo específico. Para concluir, un estudio termo-económico fue desarrollado teniendo en cuenta los costes de los principales elementos de la instalación y un valor mínimo de 2030 €/kW fue obtenido en el parámetro de Coste Específico de inversión. Además, el estudio exergético muestra que un total de 3.75 kW, 36.5 % de la tasa de destrucción total de exergía, podría ser reducida en los años futuros, teniendo en cuenta las máximas eficiencias considerando restricciones técnicas en los componentes del ciclo. / Les normatives anticontaminants per al transport propulsat per motors de combustió interna alternatius a la Unió Europea mostren límits d'emissió menors a 95 g·CO2/km per a l'any 2020. Per tal d'acomplir aquests límits, s'hauran de realitzar millores al consum de combustible dels vehicles. Una de les principals pèrdues als Motors de combustió interna alternatius (MCIA) ocorre a la línia d'escapament. Els MCIA transformen l'energia química en energia mecànica a través de la combustió; però, únicament el 15-32% d'aquesta energia és usada per produir treball, mentre que la major part és desaprofitada a través dels gasos d'escapament i l'aigua de refrigeració del motor. Per això, aquestes fonts d'energia poden ser utilitzades per millorar l'eficiència global del vehicle. Considerant aquestes dues fonts d'energia, els gasos d'escapament mostren un potencial major de recuperació d'energia residual debut al seu major contingut exergètic. De tots els tipus de Sistemes de Recuperació d'Energia Residual, els Cicles Rankine són considerats com els candidats més prometedors per millorar l'eficiència dels MCIA. No obstant, la implementació d'aquesta tecnologia en els vehicles de passatgers moderns requereix un desenvolupament addicional per aconseguir una integració compacta i una bona controlabilitat del motor. Mentre que les aplicacions industrials normalment operen en punts d'operació estacionaris, en el cas dels vehicles amb MCIA hi han importants reptes a solucionar tenint en compte el funcionament en condicions variables del motor i el seu impacte en la manera de conducció quotidiana del usuari. Aquesta Tesi contribueix al coneixement i caracterització d'un Cicle Rankine Orgànic (ORC) acoblat amb un motor de combustió interna alternatiu (MCIA) utilitzant etanol com a fluid de treball i un expansor tipus Swash-plate com a màquina expansora. El principal objectiu d'aquest treball de recerca és obtenir i quantificar el potencial dels ORCs per a la recuperació de l'energia residual en motors d'automoció. Per aconseguir-ho, una instal·lació experimental amb un ORC va ser dissenyada i construïda a l'Institut "CMT- Motores Térmicos" (Universitat Politècnica de València). Esta installació pot ser acoblada a diferents tipus de MCIAs. Mitjançant assajos experimentals en aquesta installació, una estimació de les principals variables del cicle va ser obtinguda tant en punts estacionaris com en punts transitoris. Un potencial de millora al voltant d'un 3.7% pot ser aconseguida en punts d'alta càrrega instal·lant un ORC acoblat a un motor gasolina turboalimentat. Pel que fa a les condicions transitòries, un control senzill i robust basat en PIDs adaptatius permet el control del ORC en perfils de conducció reals. Les condicions ideals per a testejar i validar el control de l'ORC són alta càrrega al motor començant amb el motor en calent per aconseguir altes temperatures d'escapament que justifiquen la viabilitat d'aquests cicles. Per tractar d'aprofundir en la viabilitat i característiques d'aquesta aplicació particular, diversos estudis teòrics van ser realitzats. Un model 1D va ser desenvolupat usant el programari LMS Imagine.Lab Amesim. Un potencial de millora al voltant d'un 2.5% en el rendiment efectiu del motor va ser obtingut en condicions transitòries en els punts d'alta càrrega com una conseqüència directa de la reducció de 23.5 g/kWh al consum específic. Per concloure, un estudi termo-econòmic va ser desenvolupat tenint en compte els costos dels principals elements de la installació i un valor mínim de 2030 €/kW va ser obtingut en el paràmetre del Cost Específic d'Inversió. A més, l'estudi exergètic mostra que un total de 3.75 kW, 36.5% de la taxa de destrucció total d'exergia, podria ser recuperat en un pròxim, considerant restriccions tècniques en els components del cicle i tenint en compte les màximes eficiències que es poden aconseguir. / Royo Pascual, L. (2017). Study of Organic Rankine Cycles for Waste Heat Recovery in Transportation Vehicles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84013 / TESIS

The process to induct air into engine cylinders, via the air inlet system and cylin-der port valves, is referred to as the "gas-exchange". Control is achieved by theturbo-charger, the intake throttle plate and the variable valve timing (VVT) sys-tem. These actuation systems traditionally use separate control with indepen-dent SISO feedback. There are however physical couplings that affect the con-trol performance. This thesis work looks at MPC control methods for a robustcontrol strategy. MPC methods are typically used for systems with slow dynam-ics, due to computational limits. But new advances in CPU performance shouldallow for real-time implementations for engine control. / <p>Redan framlagt exjobbet</p>

This thesis is treating the modelling of a thermocouple (tc) to compensate forheat transfers due to convection, radiation and conduction when performingtemperature measurements in an SI-engine. An experiment plan was developedwhich covered experiments in an stc-rig and on a 4-cylinder SI-engine. The measurementsin the stc-rig was mainly to develop the model, while the measurementsin the engine lab was mainly to examine the characteristics of the engineand evaluate the modelled tc.Measurements with an exposed thin tip tc in the stc-rig showed a symmetricaltemperature profile in the pipe. By examining how the 1.5 mm tc behaved inthis environment with known gas temperature profile, the obtained knowledgecould be applied to cross-sectional measurements in the SI-engine. It was foundthat the temperature profile in the engine deviated from the temperature profilemeasured in the stc-rig. The temperature was higher near the top of the pipethan in the center and lower part. In the horizontal direction, the temperaturewas found to be constant.Conclusions drawn from measurements in the engine lab points to that the crosssectionaltemperature and mass flow profiles have a strong connection with theengine’s operation point. The cross-sectional profiles, along with respective profileover time, is crucial when estimating the energy content of an exhaust gaspulse.The inverted sensor model with optimized parameters could estimate the meanvalue of the measured gas temperature during stationary runs within 6 degC.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

Das Konzept „Downsizing“ für Otto- und Dieselmotoren zur Verbesserung von Kraftstoffverbrauch und Schadstoffemission ist inzwischen durch viele praktische Beispiele und theoretische Untersuchungen zweifelsfrei bestätigt worden. Da „Downsizing“ aber untrennbar mit der Aufladung verbunden ist, wächst der Bedarf nach Aufladetechnologien, die das Hauptmanko des „Downsizing“ – das mangelhafte Drehmoment bei niedriger Motordrehzahl – überwinden. Mit zunehmender spezifischer Leistung und damit höheren Aufladegraden tritt diese Problematik immer stärker in den Vordergrund. Vor diesem Hintergrund hat sich für den Pkw-Dieselmotor die Aufladung mit VTG durchgesetzt. Beim Ottomotor wurde bislang der Schritt vom einfacheren Wastegate-Lader zur VTG noch nicht unternommen. Die Gründe dafür sind insbesondere in der höheren thermischen Belastung, aufgrund der höheren Abgastemperatur, und der größeren Luftdurchsatzspanne zu finden. Andererseits besteht inzwischen speziell beim Ottomotor ein großer Bedarf bezüglich der Verbesserung des Kraftstoffverbrauches und der Fahrdynamik in Kombination mit der Turboaufladung. Vor dem Hintergrund der in den letzten Jahren durchgeführten Weiterentwicklungen auf dem Gebiet der Benzindirekteinspritzung und der Aufladetechnik, stellt sich inzwischen verstärkt die Frage, ob durch den Einsatz einer VTG am Ottomotor ähnlich große Verbrauchseinsparungen und Verbesserungen in der Fahrdynamik erzielt werden können, wie dies vor einigen Jahren beim Pkw-Dieselmotor der Fall war. Im Rahmen der durchgeführten Arbeit wurden die Potentiale einer VTG an einem direkteinspritzenden Ottomotor eingehend durch Experimente und Motorprozesssimulation untersucht. Bei der direkten Übertragung der heute üblichen Diesel-VTG-Technik auf die Anwendung am Ottomotor können allerdings nur unwesentliche Verbesserungen beim spezifischen Kraftstoffverbrauch erzielt werden. Um die volle Drehzahlspanne des Ottomotors in seiner Basisabstimmung bedienen zu können, muss der Verstellbereich der VTG extrem ausgereizt werden, was Wirkungsgradnachteile mit sich bringt. Mit dem Übergang auf ein 2-flutiges Zwillingsstromturbinengehäuse in Kombination mit VTG wird es möglich, den Gaswechsel des Motors zu verbessern, da der Auslassvorgang der einzelnen Zylinder weniger durch die anderen Zylinder behindert wird. Der Effekt ist allerdings wesentlich schwächer ausgeprägt als bei einem 2-flutigen Wastegate Lader, da hier die Flutentrennung bis kurz vor das Turbinenrad erfolgen kann. Bei der VTG-Zwillingsstromturbine endet die Trennung konstruktionsbedingt bereits vor dem Leitgitter. Im Bereich des beschaufelten Ringkanales treffen die beiden bis dorthin getrennten Abgasstränge aufeinander und beeinflussen sich hier wieder gegenseitig, wobei die negativen Auswirkungen geringer sind als bei einer 1-flutigen Turbine, ganz ohne Trennung im Turbinengehäuse. Die bessere Nutzung der kinetischen Energie aus dem Vorauslassstoß, die bei Stoßaufladung mit getrennt geführten Abgaskanälen üblicherweise möglich ist, kann allerdings bei einer VTG-Turbine nicht erreicht werden. Speziell im unteren Motordrehzahlbereich, wo die Leitschaufeln weit geschlossen sind, werden die Druckpulsationen stark gedämpft und haben somit nur noch einen geringen Anteil an der Totalenthalpie des Abgases. Wie sich aus den Untersuchungen zeigte, kann dieser Nachteil der VTG aber durch den kleineren Turbinendurchsatz bei kleiner Schaufelstellung überkompensiert werden, wodurch das Drehmoment bei niedrigen Motordrehzahlen angehoben werden kann. Eine wesentlich bessere Flutentrennung kann durch die Verwendung einer VTG-Doppelstromturbine erreicht werden. Durch zwei über den Turbinenumfang getrennt geführte Spiralkanäle können die Überströmquerschnitte verkleinert, und damit die gegenseitige Beeinflussung der Abgasströme wesentlich verringert werden. Die Verhältnisse sind in dieser Ausführung vergleichbar mit Wastegate- Zwillingsstromturbinen, was die Effektivität der Flutentrennung anbelangt. Das volle Potential dieser optimierten Flutentrennung kann durch eine geänderte Applikation der Nockenwellenverstellungen im Motorkennfeld ausgeschöpft werden. Es ist damit möglich, längere Ventilüberschneidungen im unteren Motordrehzahlbereich zu realisieren und damit den Spülluftanteil in diesem Kennfeldbereich wesentlich zu steigern. Diese Maßnahme hat einen sehr positiven Einfluss auf die Motorbetriebswerte aufgrund: • Verringerter Klopfempfindlichkeit durch Reduktion des Restgasanteiles. • Absenkung der mittleren Abgastemperatur vor Turbine und damit der Möglichkeit, das Verbrennungsluftverhältnis anzuheben. • Verringerung der notwendigen Durchsatzspanne für Verdichter und Turbine und damit der Möglichkeit den Lader bei besseren Wirkungsgraden zu betreiben. Aufgrund des mit der Doppelstromanordnung begrenzten Zuströmquerschnittes über den Umfang der Turbine (180° pro Turbinenstrang) stellt sich allerdings ein geringerer Maximaldurchsatz für die Turbine ein. Die Simulationsergebnisse haben gezeigt, dass dadurch der mittlere Abgasdruck vor Turbine im oberen Volllastdrehzahlbereich ansteigt. Um dies zu verhindern, kann die Doppelstromturbine mit einer so genannten Stau–Stoß–Umschaltung versehen werden, mit der die beiden Turbinenstränge bei hohen Motordrehzahlen verbunden werden. Bei geöffnetem Umschaltventil kann sich das Abgas auf beide Turbinenstränge verteilen, und die Pulsation wird zusätzlich reduziert. Beide Effekte bewirken ein Absinken der Turbinenleistung und damit die gewünschte Begrenzung des Ladedruckes. Gleichzeitig ist es auch möglich, das Stoß–Stau–Umschaltventil als zusätzliches Wastegate zu betreiben, wodurch der Durchsatzbereich der Turbine noch weiter gesteigert werden kann. Die Kombination der geschilderten Maßnahmen: • VTG mit Doppelstromturbine • Stoß-Stau-Umschaltung • Vergrößerte Ventilüberschneidung hat bei den durchgeführten Untersuchungen zu einer Steigerung des stationären Volllastdrehmomentes von 40 % bei nM = 1500 1/min geführt, bei gleichzeitiger Verbesserung des Spüldruckgefälles um ca. 400 mbar im Nennleistungspunkt gegenüber dem 1-flutigen Wastegate-Basislader. Im Instationärbetrieb konnte am Beispiel eines Lastsprunges bei nM = 1800 1/min eine Verkürzung der Zeit bis zum Erreichen von 90 % des Nennmomentes um ca. 50 % festgestellt werden. Obgleich auf Basis der untersuchten Varianten bezüglich der aerodynamischen Auslegung der Einzelkomponenten, der Regelbarkeit der VTG und der mechanischen Haltbarkeit noch weitere Entwicklungsaktivitäten notwendig sein werden, kann aufgrund der sehr positiven Untersuchungsergebnisse von einem großen Potential für die Aufladung von DI-Ottomotoren mit variabler Turbinengeometrie ausgegangen werden.