Model Predictive Control of Modern High-Degree-of-Freedom Turbocharged Spark Ignited Engines with External Cooled EGR

The efficiency of modern downsized SI engines has been significantly improved using cooled Low-Pressure Exhaust Gas Recirculation, Turbocharging and Variable Valve Timing actuation. Control of these sub-systems is challenging due to their inter-dependence and the increased number of actuators associated with engine control. Much research has been done on developing algorithms which improve the transient turbocharged engine response without affecting fuel-economy. With the addition of newer technologies like external cooled EGR the control complexity has increased exponentially. This research proposes a methodology to evaluate the ability of a Model Predictive Controller to coordinate engine and air-path actuators simultaneously. A semi-physical engine model has been developed and analyzed for non-linearity. The computational burden of implementing this control law has been addressed by utilizing a semi-physical engine system model and basic analytical differentiation. The resulting linearization process requires less than 10% of the time required for widely used numerical linearization approach. Based on this approach a Nonlinear MPC-Quadratic Program has been formulated and solved with preliminary validation applied to a 1D Engine model followed by implementation on an experimental rapid prototyping control system. The MPC based control demonstrates the ability to co-ordinate different engine and air-path actuators simultaneously for torque-tracking with minimal constraint violation. Avenues for further improvement have been identified and discussed

Analysis and Optimization of the Transient Operation of Gasoline Turbocharged Direct Injection Engines Under High EGR Conditions

[ES] El transporte por carretera es uno de los sectores que más contribuyen al cambio climático. Por ello, muchos gobernantes a nivel mundial están promoviendo una transición hacia medios de transporte sostenibles que no dependan de combustibles fósiles. Sin embargo, debido a la falta de competitividad de las alternativas actuales, no parece factible, en el corto plazo, reducir significativamente el uso de los motores de combustión. Así pues, es probable que los motores de gasolina (MEP) mantengan su papel dominante en el sector automotriz durante los próximos años. De ahí que sea crucial seguir mejorando estos motores a fin de reducir su huella de carbono. Actualmente, es habitual fabricar motores MEP de pequeña cilindrada ("downsizing") con sistemas de sobrealimentación e inyección directa, a fin de reducir el consumo de combustible y las emisiones de CO2. Además, en la última década, se ha demostrado que la recirculación de gases de escape (EGR) puede mejorar la eficiencia de los motores MEP entre un 3 % y un 6 %, dependiendo del grado de carga. Como desventaja, para poder extraer todo el potencial de la estrategia EGR, es necesario trabajar con altas tasas de EGR, lo que puede causar ciertos problemas en condiciones transitorias. En esta tesis, se ha demostrado que el uso de altas tasas de EGR a través de sistemas de baja presión en motores MEP turboalimentados puede ralentizar la respuesta del motor y provocar fallos de encendido durante maniobras de aceleración y desaceleración, respectivamente. Con la entrada en vigor de nuevos procedimientos de homologación de vehículos, como el WLTP (Worldwide harmonized Light vehicle Test Procedure), donde las operaciones transitorias tienen un peso importante, los fabricantes buscan que sus motores consuman y emitan menos en un amplio rango de condiciones de operación, tanto estacionarias como transitorias. Por ello, el objetivo principal de esta tesis es analizar y optimizar el funcionamiento, en condiciones transitorias, de los motores MEP que operan con altas tasas de EGR. Para ello, se ha empleado un motor de gasolina (Euro 6) de 1.3l turboalimentado con inyección directa, distribución variable y turbina de geometría variable. Se ha desarrollado un modelo unidimensional (1D) del motor para el estudio de la fluidodinámica y los fenómenos de transporte en su interior. Por otro lado, se ha ensayado el motor para calibrar el modelo 1D y evaluar aspectos difícilmente predecibles con dicho modelo, como las emisiones contaminantes y la estabilidad de la combustión. Previo al estudio en condiciones transitorias, el motor fue calibrado con EGR, y se realizaron simulaciones para determinar el consumo de un vehículo convencional y otro híbrido, ambos con EGR, durante un ciclo WLTP. Finalmente, se concluyó que ciertas estrategias orientadas a mejorar el proceso de renovación de la carga pueden resolver la problemática del uso del EGR en condiciones transitorias. Eso sí, implementar dichas estrategias conllevaría un aumento en complejidad y costes.[CA] El transport per carretera és un dels sectors que més contribueixen al canvi climàtic. Per això, molts governants a nivell mundial estan promovent una transició cap a mitjans de transport sostenibles que no depenguen de combustibles fòssils. No obstant això, a causa de la falta de competitivitat de les alternatives actuals, no sembla factible, en el curt termini, reduir significativament l'ús dels motors de combustió. Així doncs, és probable que els motors de gasolina (MEP) mantinguen el seu paper dominant en el sector automotriu durant els pròxims anys. D'ací ve que siga crucial continuar millorant aquests motors a fi de reduir la seua petjada de carboni. Actualment, és habitual fabricar motors MEP de xicoteta cilindrada ("downsizing") amb sistemes de sobrealimentació i injecció directa, a fi de reduir el consum de combustible i les emissions de CO2. A més, en l'última dècada, s'ha demostrat que la recirculació de gasos d'escapament (EGR) pot millorar l'eficiència dels motors MEP entre un 3% i un 6%, depenent del grau de càrrega. Com a desavantatge, per a poder extraure tot el potencial de l'estratègia EGR, és necessari treballar amb altes taxes de EGR, la qual cosa pot causar uns certs problemes en condicions transitòries. En aquesta tesi, s'ha demostrat que l'ús d'altes taxes de EGR a través de sistemes de baixa pressió en motors MEP turboalimentats pot alentir la resposta del motor i provocar fallades d'encesa durant maniobres d'acceleració i desacceleració, respectivament. Amb l'entrada en vigor de nous procediments d'homologació de vehicles, com el WLTP (Worldwide harmonized Light vehicle Test Procedure), on les operacions transitòries tenen un pes important, els fabricants busquen que els seus motors consumisquen i emeten menys en un ampli rang de condicions d'operació, tant estacionàries com transitòries. Per això, l'objectiu principal d'aquesta tesi és analitzar i optimitzar el funcionament, en condicions transitòries, dels motors MEP que operen amb altes taxes de EGR. Per a això, s'ha emprat un motor de gasolina (Euro 6) de 1.3l turboalimentat amb injecció directa, distribució variable i turbina de geometria variable. S'ha desenvolupat un model unidimensional (1D) del motor per a l'estudi de la fluidodinàmica i els fenòmens de transport en el seu interior. D'altra banda, s'ha assajat el motor per a calibrar el model 1D i avaluar aspectes difícilment predictibles amb aquest model, com les emissions contaminants i l'estabilitat de la combustió. Previ a l'estudi en condicions transitòries, el motor va ser calibrat amb EGR, i es van realitzar simulacions per a determinar el consum d'un vehicle convencional i un altre híbrid, tots dos amb EGR, durant un cicle WLTP. Finalment, es va concloure que unes certes estratègies orientades a millorar el procés de renovació de la càrrega poden resoldre la problemàtica de l'ús del EGR en condicions transitòries. Això sí, implementar aquestes estratègies comportaria un augment en complexitat i costos.[EN] Road transport is a major contributor to climate change. However, given the lack of competitiveness of fossil fuel-free alternatives, it does not seem possible to reduce the dependence on the internal combustion engine (ICE) as rapidly as planned by the authorities. Advanced gasoline engines will therefore hold a high market share in the automobile industry in the following years, at least during the next decade, either working in conventional or hybrid powertrains. Hence it is essential to keep improving these engines to reduce the negative impact of light-duty vehicles on the environment. The most used strategy to reduce fuel consumption and CO2 emissions in current spark-ignition (SI) gasoline engines is downsizing combined with direct injection (DI). Besides, downsizing must go hand in hand with turbocharging to maintain peak power. It is also proven that exhaust gas recirculation (EGR) can improve fuel economy in SI engines by 3-6% at medium and high loads. As a disadvantage, extracting the full benefit from EGR requires operating with high recirculation rates (close to the EGR dilution limit), leading to some issues under transient conditions. In this thesis, it is demonstrated that high EGR operation through long-route systems in turbocharged engines can potentially originate combustion instabilities and poor engine response during load-decrease (tip-out) and load-increase (tip-in) maneuvers, respectively. Transient operations are especially important for manufacturers since the implementation of the Worldwide harmonized Light vehicle Test Procedure (WLTP). The present thesis is therefore devoted to analyzing and optimizing the gasoline engine performance under high EGR conditions during relevant transient maneuvers. To this end, a Euro-6 1.3L turbocharged DI SI gasoline engine with a variable geometry turbine was employed. A 1D model of this ICE was developed to assess fluid dynamics and transport phenomena. Engine tests were also performed to validate the 1D model and evaluate torque response, combustion stability, and raw exhaust emissions. Before addressing the study of transient maneuvers, the engine calibration with EGR was carried out, and 0D conventional and hybrid vehicle simulations were done to determine the EGR benefit in fuel economy under WLTP driving conditions. Finally, tip-in and tip-out results revealed that some air management strategies are effective in meeting the transient EGR challenges in SI engines, but at the expense of increased complexity and costs.González Domínguez, D. (2023). Analysis and Optimization of the Transient Operation of Gasoline Turbocharged Direct Injection Engines Under High EGR Conditions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/19385

Observations on and potential trends for mechanically supercharging a downsized passenger car engine:a review

Engine downsizing is a proven approach for achieving a superior fuel efficiency. It is conventionally achieved by reducing the swept volume of the engine and by employing some means of increasing the specific output to achieve the desired installed engine power, usually in the form of an exhaust-driven turbocharger. However, because of the perceptible time needed for the turbocharger system to generate the required boost pressure, a characteristic of turbocharged engines is their degraded driveability in comparison with those of their naturally aspirated counterparts. Mechanical supercharging refers to the technology that compresses the intake air using the energy taken directly from the engine crankshaft. It is anticipated that engine downsizing which is realised either solely by a supercharger or by a combination of a supercharger and a turbocharger will enhance a vehicle’s driveability without significantly compromising the fuel consumption at an engine level compared with the downsizing by turbocharging. The capability of the supercharger system to eliminate the high exhaust back pressure, to reduce the pulsation interference and to mitigate the surge issue of a turbocharged engine in a compound-charging system offsets some of the fuel consumption penalty incurred in driving the supercharger. This, combined with an optimised down-speeding strategy, can further improve the fuel efficiency performance of a downsized engine while still enhancing its driveability and performance at a vehicle level. This paper first reviews the fundamentals and the types of supercharger that are currently used, or have been used, in passenger car engines. Next, the relationships between the downsizing, the driveability and the down-speeding are introduced to identify the improved synergies between the engine and the boosting machine. Then, mass production and prototype downsized supercharged passenger car engines are briefly described, followed by a detailed review of the current state-of-the-art supercharging technologies that are in production as opposed to the approaches that are currently only being investigated at a research level. Finally, the trends for mechanically supercharging a passenger car engine are discussed, with the aim of identifying potential development directions for the future. Enhancement of the low-end torque, improvement in the transient driveability and reduction in low-load parasitic losses are the three main development directions for a supercharger system, among which the adoption of a continuously variable transmission to decouple the supercharger speed from the engine speed, improvement of the compressor isentropic and volumetric efficiency and innovation of the supercharger mechanism seem to be the potential trend for mechanically supercharging a passenger car engine. </jats:p

Assessment of fuel consumption reduction strategies on a gasoline turbocharged direct injection engine with a cooled EGR system

[EN] This research work presents the study of a low pressure EGR loop influence on a SI gasoline turbocharged direct injection engine in steady and transient testing conditions, with an optimization process of the original engine calibration in order to minimize the engine fuel consumption when cooled EGR is introduced in steady testing conditions. The cooled EGR strategy was also evaluated operating in synergy with other fuel consumption reduction strategies, such as: lean burn, multi-injection, higher coolant temperature and in-cylinder induced swirl motion. To fulfill the main objectives of this research work, firstly, a methodical process was followed, where a global methodology was first developed in order to obtain high accuracy engine tests, based on the experimental tools chosen that could comply with the requirements of the testing conditions, and the appropriate theoretical tools and procedure to post-process the tests performed. Secondly, a specific methodology was developed for each stage of the study and testing conditions, taking into account optimization processes or parametric tests in order to study the effect of a single parameter on engine's outputs or optimize an engine parameter in order to minimize the engine fuel consumption. As a first stage of the study, a basic analysis of the impact of cooled EGR on the engine combustion, performance, air management and exhaust emissions is presented. Afterwards, an optimization of the combustion phasing in order to minimize the fuel consumption was performed, and therefore the potential of cooled EGR in order to reduce the engine fuel consumption was observed for low load, part load and full load engine conditions, for two different engine speeds. In addition, a study in transient conditions of the engine operating with cooled EGR was performed. NEDC cycles were performed with different EGR valve openings and therefore a comparison of different cooled EGR rates influence on the engine performance, air management and accumulated exhaust emissions was presented. The second stage, consisted in a methodology developed to optimize the VVT setting and injection timing, for part load engine conditions, in order to maximize the cooled EGR potential to reduce engine fuel consumption. After this optimization, a synergy analysis of the optimum engine condition operating with cooled EGR and three other engine fuel consumption reduction strategies was performed. These strategies were tested to investigate and evaluate the potential of increasing the cooled EGR operational range to further decrease the engine fuel consumption. Furthermore, a basic study of the potential to reduce the engine fuel consumption and impact on combustion, air management and exhaust emissions of a lean burn strategy, in part load engine conditions, was presented as introduction of the final study of the cooled EGR strategy operating in synergy with the lean burn strategy in order to investigate the potential to control the exhaust emissions and reduce the engine fuel consumption.[ES] El objetivo de este trabajo de investigación es estudiar la influencia de un lazo de baja presión de EGR en las prestaciones de un motor de gasolina de encendido provocado turbosobrealimentado e inyección directa, en condiciones de ensayos estacionarios y transitorios, con un proceso de optimización de la calibración original del motor para minimizar el consumo de combustible del motor. La estrategia de "cooled EGR" fue también evaluada operando en sinergia con otras estrategias usadas para reducir el consumo de combustible del motor, entre ellas: mezcla pobre, múltiples inyecciones, operación a alta temperatura del fluido refrigerante del motor y movimiento de "swirl" inducido en el cilindro. Para cumplir con los objetivos mencionados, se siguió un proceso metódico donde previamente se desarrolló una metodología global para obtener resultados de indudable calidad, basados en el uso de herramientas experimentales que cumplieran con los requerimientos de las condiciones de ensayo, y las apropiadas herramientas teóricas y procedimiento para post-procesar los ensayos realizados. En segundo lugar, se desarrolló una metodología específica para cada etapa del estudio, teniendo en cuenta los procesos de optimización o estudios paramétricos que se pudieran realizar. Como primera etapa, se presenta un estudio básico del impacto del "cooled EGR" en la combustión, prestaciones, renovación de la carga y emisiones contaminantes del motor. Seguidamente, se procedió a la optimización del centrado de la combustión con la finalidad de minimizar el consumo de combustible del motor y poder analizar el potencial del "cooled EGR" como estrategia de reducción de consumo de combustible. El estudio presentado se realizó para baja, media y alta carga del motor con dos diferentes regímenes de giro del motor. Adicionalmente, se llevó a cabo un estudio del motor operando en condiciones transitorias con "cooled EGR". Se realizaron una serie de ensayos usando el ciclo NEDC como base y se probaron diferentes estrategias sencillas de control de la apertura de la válvula de EGR para analizar la influencia del "cooled EGR" en condiciones transitorias. La segunda etapa consiste en el desarrollo de una metodología para optimizar los parámetros del diagrama de distribución (VVT) y el inicio de inyección, para cargas medias del motor, con la finalidad de maximizar el potencial de reducción de consumo de combustible de la estrategia "cooled EGR". Una vez realizada la optimización, se llevó a cabo un estudio usando la configuración óptima encontrada, operando en sinergia con otras tres estrategias usadas para reducir el consumo de combustible del motor. Estas estrategias fueron evaluadas con la finalidad de incrementar el rango de operación de la estrategia "cooled EGR" para lograr reducir aún más el consumo de combustible del motor. Adicionalmente, se llevó a cabo un estudio básico sobre la influencia de operar con mezcla pobre en la combustión, prestaciones, renovación de la carga y emisiones contaminantes del motor, como introducción al último estudio llevado a cabo sobre la posibilidad de usar la estrategia de mezcla pobre en conjunto con la estrategia de "cooled EGR", con la finalidad de analizar el potencial de controlar las emisiones contaminantes y reducir el consumo de combustible del motor al mismo tiempo.[CA] L'objectiu d'este treball d'investigació és estudiar la influència d'un llaç de baixa pressió d'EGR en les prestacions d'un motor de gasolina d'encesa provocat turbosobrealimentat i injecció directa, en condicions d'assajos estacionaris i transitoris, amb un procés d'optimització del calibratge original del motor per a minimitzar el consum de combustible del motor. L'estratègia de "cooled EGR" va ser també avaluada operand en sinergia amb altres estratègies usades per a reduir el consum de combustible del motor, entre elles: mescla pobra, múltiples injeccions, operació a alta temperatura del fluid refrigerant del motor i moviment de `"swirl" induït en el cilindre. Per a complir amb els objectius mencionats, es va seguir un procés metòdic on prèviament es va desenrotllar una metodologia global per a obtindre resultats d'indubtable qualitat, basats en l'ús de ferramentes experimentals que compliren amb els requeriments de les condicions d'assaig, i les apropiades ferramentes teòriques i procediment per a post- processar els assajos realitzats. En segon lloc, es va desenrotllar una metodologia específica per a cada etapa de l'estudi, tenint en compte els processos d'optimització o estudis paramètrics que es pogueren realitzar. Com a primera etapa, es presenta un estudi bàsic de l'impacte del "cooled EGR" en la combustió, prestacions, renovació de la càrrega i emissions contaminants del motor. A continuació, es va procedir a l'optimització del centrat de la combustió amb la finalitat de minimitzar el consum de combustible del motor i poder analitzar el potencial del "cooled EGR" com a estratègia de reducció de consum de combustible. L'estudi presentat es va realitzar per a baixa, mitja i alta càrrega del motor amb dos diferents règims de gir del motor. Addicionalment, es va dur a terme un estudi del motor operand en condicions transitòries amb "cooled EGR". Es van realitzar una sèrie d'assajos usant el cicle NEDC com a base i es van provar diferents estratègies senzilles de control de l'obertura de la vàlvula d'EGR per a analitzar la influència del "cooled EGR" en condicions transitòries. La segona etapa consistix en el desenrotllament d'una metodologia per a optimitzar els paràmetres del diagrama de distribució (VVT) i l'inici d'injecció, per a càrregues mitges del motor, amb la finalitat de maximitzar el potencial de reducció de consum de combustible de l'estratègia "cooled EGR". Una vegada realitzada l'optimització, es va dur a terme un estudi usant la configuració òptima trobada, operant en sinergia amb altres tres estratègies usades per a reduir el consum de combustible del motor. Estes estratègies van ser avaluades amb la finalitat d'incrementar el rang d'operació de l'estratègia "cooled EGR" per a aconseguir reduir encara més el consum de combustible del motor. Addicionalment, es va dur a terme un estudi bàsic sobre la influència d'operar amb mescla pobra en la combustió, prestacions, renovació de la càrrega i emissions contaminants del motor, com a introducció a l'últim estudi dut a terme sobre la possibilitat d'usar l'estratègia de mescla pobra en conjunt amb l'estratègia de "cooled EGR", amb la finalitat d'analitzar el potencial de controlar les emissions contaminants i reduir el consum de combustible del motor al mateix temps.Rivas Perea, ME. (2016). Assessment of fuel consumption reduction strategies on a gasoline turbocharged direct injection engine with a cooled EGR system [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68497TESI

An investigation into electric supercharging for emission reduction by means of engine downsizing

This thesis describes an investigation into the operation and performance of internal combustion engines boosted by an electric supercharger (eSC) in combination with a turbocharger. Engine downsizing offers one of the most effective ways to meet increasingly demanding CO2 reduction targets set for the automotive vehicles. The addition of a turbocharger has enabled significant downsizing but the loss of torque at low engine speeds remains a key barrier to further downsizing. A known solution to this problem is to additionally boost the engine using a supercharger. However, until recently, this was very difficult to implement economically on engines with modest engine power suitable for small to medium sized vehicles due to the low air mass flow rates for such engines. Now, a new turbo-machinery innovation, the high forward swept TurboClaw compressor, allows significant boosting to be done at low flow rates yet with moderate compressor shaft speeds. Since this compressor can be driven at a moderate speeds, the electric motor which drives for the electric supercharger (eSC) is more affordable. The research objective was to assess this new eSC system be means of a theoretical and experimental investigation. There are two possible combinations in terms of whether the (eSC) goes before the turbocharger (ETC), or after (TEC). Employing the eSC after turbocharger generally has the advantage of broadening the eSC map, towards higher-mass flows since a denser air exits the turbo-compressor as the turbocharger provides boosted air to the system. This augments the overlap of the two operating maps for the two devices. However the real benefit of eSC in each layout depends on the engine (baseline). In this research ETC and TEC produce basically the same torque increase; the real eSC benefit is at low speed where the nominal maximum torque is recovered for all the range. However since the current drawn from the battery is a key factor for this application, the investigation shows that the thermodynamic power requested by eSC is less than 1.5kW for ETC layout while this value is 2.5kW for TEC layout. Therefore ETC layout was chosen as the final configure to be implemented on the selected vehicle for the dyno test purposes since it requires less power. Theoretical models for the engine, turbocharger and TurboClaw eSC including electric motor were created and validated. The system of all components was designed including control system and strategy. A key result showed that the eSC was found to boost the torque of a 1.0 litre turbocharged engine by 125% and 58% for 1000 rpm and 1200 rpm respectively

Study of externally waste-gated turbine performance under steady and pulsating inlet conditions for improved turbocharger matching

The demand for drastic reduction in CO2 emission among road vehicles has seen downsizing becoming a megatrend in modern engine developments due to its benefits in reducing throttling loss and improvement in engine efficiency. In light of this, turbocharging is seen as one of the key enabling technologies and therefore carries along with it an ever-increasing challenge in terms of system-matching as the device is required to operate in ranges never encountered before. The increasing reliance on 1-D engine performance simulation tools calls for more accurate representation of the turbocharger model. The present study assessed the turbocharger turbine maps for use in commercial 1-D gas dynamics engine code from several aspects, namely the width of the map and the representation of turbine unsteady performance in the virtual environment. Furthermore, the present work assessed the performance of turbine under waste-gated operations. For this, an experimental work has been carried out on a bespoke waste-gated turbine layout over a wide range of operating conditions. The performance of the radial turbine under steady inlet conditions was evaluated for different waste-gate openings, at various points along several speed-lines. Then the unsteady tests saw the turbine performance evaluated at various sets of pulse frequencies, turbine loadings and waste-gate openings. Analysis of this study include the impact of turbine map width on the turbine performance modelling in a commercial 1-D gas dynamics engine simulation software and subsequently the prediction of the engine’s performance. This simulation work is carried out based on an actual heavily downsized gasoline engine with a series super-turbocharging system. The study also examined the method of incorporating the effects of turbine unsteady performance under waste-gated and non-waste-gated conditions in the performance maps used in 1-D code and evaluate its impact on the engine performance prediction. The outcome of the study aims at providing a deeper understanding on the unsteady performance of a turbocharger turbine which will lead to improved turbocharger-engine matching methods in the future.Open Acces

Modeling of Turbulence, Combustion and Knock for Performance Prediction, Calibration and Design of a Turbocharged Spark Ignition Engine

In this thesis work, a downsized VVA Spark Ignition engine is numerically and experimentally studied. In particular, the following topics are considered: •In-cylinder turbulence and combustion processes; •Knock and cycle by cycle variation (CCV) phenomena; •Techniques aiming to mitigate knock occurrence and improve fuel economy such as EGR and water injection methods; •Intake system redesign to reduce the emitted gas-dynamic noise; •Engine calibration. A deep experimental campaign is carried out to characterize the engine behaviour. Indeed, engine system is investigated both in terms of the overall performance (torque, power, fuel consumption, air flow rate, boost pressure etc.) and of the intake gas-dynamic noise at full load operation. In addition, proper experimental analyses are peformed on the engine to characterize the CCV phenomenon and the knock occurrence. Measured data are post-processed to derive experimental parameters which syntetize CCV and knock levels, according to the engine operating conditions. A 1D CFD model of the whole engine is realized in GT-PowerTM environment. Refined “in-house developed” sub-models capable to reproduce turbulence, combustion, CCVs and knock processes are introduced into 1D code through user routines. First of all, the whole engine model is validated against the experimental data both in terms of overall performance parameters and ensemble averaged pressure cycles and intake gas-dynamic noise at part and full load operation. Cycle by cycle variation is reproduced through a proper correlation and consequently a representative faster than average in-cylinder pressure cycle is obtained. Then, the knock model, with reference to the latter pressure cycle, allows to evaluate a proper knock index and to identify the knock limited spark advance (KLSA), basing on the same threshold level adopted in experimental knock analysis. In this way, the knock model taking into account the CCV is validated at full load operation. Once validated, the original engine architecture is modified by virtually installing a “Low pressure” EGR system. 1D simulations accounting for various EGR rates and mixture leaning are performed at full load points, showing improvements in the fuel economy with the same knock intensity of the base engine configuration. Water injection technique is also investigated by virtually mounting a water injector in the intake runners for each engine cylinder. In a similar way, 1D analyses are carried out for various water/fuel and air-to-fuel ratios, highlightinig BSFC improvements at full load operation. Since the engine under study is characterized by higher intake gas-dynamic noise levels, a partial redesign of the intake system is properly identified and subsequently tested with 1D and 3D CFD simulations to numerically quantify the gains in terms of reduction in the gas-dynamic noise emitted at the intake mouth. Finally, a numerical methodology aiming to calibrate the considered engine at high load knock-limited and at part load operations is developed. First, it shows the capability to identify with satisfactory accuracy the experimentally advised engine calibration. In addition, it allows the comparison of different intake valve strategies, underlining, in certain engine operating conditions, the fuel consumption benefits of an early intake valve closure (EIVC) strategy with respect to a Full Lift one, due to a better combustion phasing and a reduced mixture over-fuelling. The developed automatic procedure presents the capability to realize a “virtual” engine calibration on completely theoretical basis and proves to be very helpful in reducing time and costs related to experimental activities at the test bench

Trends and Limits of Two-Stage Boosting Systems for Automotive Diesel Engines

Internal combustion engines developments are driven by emissions reduction and energetic efficiency increase. To reach the next standards, downsized/downspeeded engines are required to reduce fuel consumption and CO2 emissions. These techniques place an important demand on the charging system and force the introduction of multistage boosting architectures. With many possible arrangements and large number of parameter to optimize, these architectures present higher complexity than current systems. The objective of this thesis has thus been to investigate the potential of two-stage boosting architectures to establish, for the particular case of passenger car downsized/downspeeded Diesel engines, the most efficient solutions for achieving the forthcoming CO2 emissions targets. To respond to this objective, an exhaustive literature review of all existing solutions has first been performed to determinate the most promising two-stage boosting architectures. Then, a new matching methodology has been defined to optimize the architectures with, on the one hand the development of a new turbine characteristic maps representation allowing straight forward matching calculations and, on the other hand, the development of a complete 0D engine model able to predict, within a reduced computational time, the behavior of any boosting architecture in both steady state and transient operating conditions. Finally, a large parametric study has been carried out to analyze and compare the different architectures on the same base engines, to characterize the impacts of thermo-mechanical limits and turbocharger size on engine performance, and to quantify for different engine development options their potential improvements in term of fuel consumption, maximum power and fun to drive. As main contributions, the thesis provides new modeling tools for efficient matching calculations and synthesizes the main trends in advanced boosting systems to guide future passenger car Diesel engine developVarnier ., ON. (2012). Trends and Limits of Two-Stage Boosting Systems for Automotive Diesel Engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16880Palanci

Experimental Analysis and 1D Model Simulation of an Advanced Twin Stage Hybrid Boosting System

Due to the increasingly restrictive limits of pollutant emissions, electrification of automotive engines is now mandatory. For this reason, adopting hybrid boosting systems to improve brake specific fuel consumption and time-to-boost is becoming common practice. In this thesis an innovative turbocharging system is analysed, consisting in an electrically assisted radial compressor and a traditional turbocharger. As a first step, the steady-state performance of each component was measured at the University of Genoa test rig. Due to problems related to over temperature, the working time of the e-compressor coupled to the electric motor is limited avoiding an accurate evaluation of compressor efficiency. For this reason a driving system (instead of the electric machine) was designed to provide a more accurate evaluation of the compressor map. Subsequently another experimental campaign was carried out to evaluate the transient response of the entire turbocharging system. Two different layouts were compared: upstream and downstream. In the upstream configuration the electrically assisted compressor was placed in front of the traditional turbocharger, in the downstream configuration the e-compressor was positioned after the traditional turbocharger. The two different coupling configurations, upstream and downstream, were then modelled in 1-D simulation software following the dimensions and characteristics of the experimental line from which the exploited data originates. The models were first validated by emulating the steady-state condition and subsequently the transient response was simulated and analysed. Secondly, the transient response of the two layouts was compared, removing the constraints imposed by the experimental activity