Experimental and Computational Investigation of Spark Assisted Compression Ignition Combustion Under Boosted, Ultra EGR-Dilute Conditions

Low temperature combustion (LTC) engines that employ high levels of dilution have received increased research interest due to the demonstrated thermal efficiency improvements compared to the conventional Spark-Ignited (SI) engines. However, control of combustion phasing and heat release rate still remains a challenge, which limits the operating range as well as the transient operation of LTC engines. The work presented in this dissertation uses experimental and computational methods to investigate Spark Assisted Compression Ignition (SACI) combustion under boosted, stoichiometric conditions with high levels of exhaust gas recirculation in a negative valve overlap engine. Highly controlled experimental studies were performed to understand the impact of intake boosting and fuel-to-charge equivalence ratio (φ') on SACI burn rates, while maintaining constant combustion phasing near the optimal timing for work extraction. Previously unexplored conditions were targeted at intake pressures ranging from 80 kPa to 150 kPa and φ' ranging from 0.45 to 0.75, where LTC engines promise high thermodynamic efficiencies. The use of intake boosting for load expansion and dilution extension achieved up to 10% gross thermal efficiency improvement, respectively, mainly due to reduced relative heat transfer losses and better mixture thermodynamic properties. For a given spark advance, higher pressure and/or higher φ' mixtures necessitated lower unburned gas temperatures (TU) to match autoignition timing. While the overall effect of intake boost was minor on the initial flame burn rates, end-gas autoignition rates were found to approximately scale with intake pressure. Higher φ' mixtures exhibited faster initial flame burn rates but also led to a significant increase in end-gas autoignition rates. As a result, the high load limits shifted to lower φ' at higher intake pressures, creating a larger gap between the SI and SACI operating limits. Reducing the mass fraction unburned at the onset of autoignition by advancing the spark timing and lowering TU was, to some extent, effective at alleviating the excessive peak pressure rise rates. Under relatively high φ' conditions, cyclic heat release analysis results showed that the variability in autoignition timing is determined early in the cycle before any measurable pressure-based heat release. Combustion phasing retard was shown to be very effective at limiting the maximum pressure rise rates until the stability limit, primarily due to slower end-gas autoignition rates. CFD modeling results showed good trendwise agreement with the experimental results, once autoignition timing and mass fraction burned at the onset of autoignition were matched. The pre-ignition reactivity stratification of the mixture at higher intake pressures was shown to be narrower, due to both lower thermal and compositional stratification, which explained the increase in end-gas burn rates observed experimentally. The boost pressure effect on SACI end-gas burn rates using intake manifold heating was trendwise similar to the results employing residual gas heating, albeit less pronounced. Pre-ignition thermal stratification was shown to be similar irrespective of charge preheating method, even though thermal stratification of the mixtures was very different early in the compression stroke. The effect of higher pressure on mean reactivity was offset by the lower mean temperature that was needed to match autoignition timing. Under the conditions investigated, the increase in the end-gas autoignition rates with intake boost was primarily due to the narrower thermal stratification, which was effected by reduced relative heat transfer losses late in the compression stroke.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147508/1/vtrianto_1.pd

Modeling of a jet fuel spill in the groundwater at the Massachusetts Military Reservation

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1996.Includes bibliographical references (leaves 64-65).by Dimitris Triantopoulos.M.Eng

How low for how long? From a monetary policy perspective

This paper examines the impact of euro-area quantitative easing on the banking industry. We provide a dynamic threshold panel model that endogenously identifies the low threshold of the monetary policy rate. And we also provide insights into the long vs the short-run impact of quantitative easing on bank-level resilience and competition. Results show that there is a negative relationship between low rates and bank risk.. For the low levels of main refinancing operation, which is below 0.1097%, quantitative easing would reduce bank resilience, whereas for higher thresholds it will increase bank resilience. We also report the long-run impact of UMP on bank risk, as well as the short-run dynamics using a panel VAR model. This paper provides empirical estimates of low thresholds for the ECB’s rate and responses to shocks in monetary policy. The main findings of our analysis show that asymmetry is present because in a low regime we observe that an increase in MRO would decrease Z-score, increasing bank risk and reducing bank stability. Policy implications are of interest in the current conjecture that there are voices for hikes in the interest rates despite the anemic euro-area recovery and the geopolitical tensions

Measuring the efficiency and productivity of U.K. insurance market

The U.K. insurance industry has a dominant international presence, suggesting strong competitiveness and performance. Yet, its efficiency and productivity has rarely being investigated. The purpose of this paper is to provide an overview of insurers' performance in the U.K. insurance market from 1996 to 2017, using stochastic frontier analysis to measure efficiency scores and productivity at the firm level. Results show the U.K. insurance industry could improve by about 40% in terms of cost efficiency and by 70% in terms of profit efficiency. In addition, our model reveals a higher cost efficiency score compared to profit efficiency, implying that there are higher inefficiencies on the income side of the insurance industry as measured by our profit function. In terms of total factor productivity (TFP) growth, we report a steady decline over time while on average is negative. By decomposing TFP growth into its underlying components, we reveal that the reported negative trend in TFP growth over time has mainly been driven by the enhanced competition that resulted in a drop in markup, while the scale and cost efficiency has also driven TFP growth down. However, from a positive point of view, we report evidence of both β-convergence and σ-convergence in cost and profit efficiency

Dealing with 'unionistic' corporate governance in Greece

While the majority of private Greek corporations move towards an Anglo-Saxon market-orientated model of corporate governance, a number of important organizations still operate under a different model. We call this a “unionistic corporate governance” model and is dominant in almost every state owned enterprise in Greece. It is a distorted expression of the corporatist philosophy that prevailed in the wider Greek public sector according which unionists, managers and politicians ally and assure benefits in expense of the society. However, the implementation of the Economic Adjustment Programme -especially the 2nd one- affected the “unionistic acquis” and established rules that deteriorate the maneuvering leeway for the main actors. As previous attempts to modernize the regulatory and legal framework failed to change the regime, it is imperative to keep a close eye on the outcomes of the recent reforms and impose further measures to the same direction

Thermal effects in advanced Si-MOSFETs

La technologie CMOS atteint désormais des dimensions de l’ordre de 10nm et en deçà. Chercheurs et industriels tentent aujourd’hui de repousser les limites physiques imposées par cette réduction d’échelle, en agissant sur différents leviers technologiques afin d’améliorer les performances des dispositifs sans avoir à réduire davantage les dimensions. De nouvelles architectures de transistors ont ainsi été introduites, comme par exemple les transistors planaires à film mince (FDSOI), ou encore les transistors à grilles multiples (TriGate, FinFETs,…). L’intégration de nouveaux matériaux semiconducteurs (III-V, matériaux 2D…) est également envisagée pour les noeuds technologiques plus avancés (≲7nm), afin de maintenir les performances électriques. Une alternative à ce schéma est cependant envisageable avec l’intégration 3D séquentielle (baptisée CoolCubeTM, voir figure) [1]. Cette intégration consiste à fabriquer séquentiellement deux niveaux de transistors, les niveaux étant connectés en même temps que le process des transistors. Cette intégration permet d’obtenir une grande densité de transistors grâce à l’utilisation de la troisième dimension (verticale). Cette technologie requiert cependant le développement de procédés de fabrication à basse température pour l’étage supérieur des transistors afin de préserver les performances des transistors de l’étage inférieur.La thèse proposée s’inscrit dans ce contexte, en se concentrant sur l’étude des propriétés électriques de ces dispositifs 3D (étage supérieur et inférieur, influence mutuelle des deux niveaux de transistors) afin d’optimiser le fonctionnement de ceux-ci.Objectifs de la thèse: l’objectif principal est l’étude des propriétés électriques des transistors MOS CoolCube fabriqués au Léti, avec un focus particuliers sur le transport dans le canal et la fiabilité associée aux performances.Le travail demandé est en grande partie expérimental, basé sur des mesures électriques de transistors.A partir de ces différentes mesures, on cherchera, outre l’évaluation des performances générales de ces transistors, à étudier la mobilité des porteurs du canal dans les transistors haut (bas budget thermique) et bas (budget thermique additionnel), l’effet d’auto-échauffement (lié aux films minces et au volume réduit du canal) à chaque étage et celui induit par le fonctionnement d’un étage sur l’autre. On s’intéressera également à évaluer la fiabilité de chaque étage de transistors, en lien avec les autres caractéristiques électriques et les procédés technologiques utilisés.CMOS technology has now reached the size of about 10 nm and below. Researchers and manufacturers are now trying to push the physical limits imposed by scaling down, by acting on different technology levers to improve device performance without further reduce dimensions. New transistor architectures have been introduced, such as planar thin film transistors (FDSOI) or the multi-gate transistors (Trigate, FinFETs, ...). The integration of new semiconductor materials (III-V materials ... 2D) is also being considered for advanced technology nodes (≲7nm) to maintain electrical performance. An alternative to this scheme, however, is possible with sequential 3D integration (called CoolCubeTM see figure) [1]. This integration is to sequentially produce two levels of transistors, the levels being connected at the same time that the process of the transistors. This integration provides a high density of transistors through the use of the third dimension (vertical). However, this technology requires the development of low-temperature manufacturing processes for the upper stage of the transistors in order to maintain the performance of the transistors of the lower floor.The proposed thesis is in this context, focusing on the study of electrical properties of these 3D devices (upper and lower floor, mutual influence of the two levels of transistors) to optimize the operation thereof.Objectives of the thesis: the main objective is the study of electrical properties of MOS transistors manufactured CoolCube Leti, with a special focus on transport in the channel and reliability associated with the performance.The job is largely experimental, based on electrical measurements of transistors.From these measures, we will seek, in addition to assessing the overall performance of these transistors, to study the carrier mobility of the channel in the top transistors (low thermal budget) and down (additional thermal budget), the effect of self-heating (related to thin films and the reduced volume of the channel) on each floor and that induced by the operation of a stage on the other. It will also focus on assessing the reliability of each stage transistors, linked with other electrical characteristics and technological processes used.The thesis will be carried out in the laboratory of electrical characterization (LCTE) Silicon Components department Leti, in close collaboration with the laboratory 'integration-die' (LiCl)

EU financial markets and supervision: the political economy view

This thesis is a study that contributes to the comparative capitalism literature with the development of a new approach considering the organisation of the economy during the capitalism’s era of financial excess. It is a phase of the European capitalistic economy that ended “painfully” with the 2007/2008 global financial crisis and during which the indebtedness of the private and public sector was two times over the economy’s output and the size of the financial system ended up five times the size of the economy. This approach is labelled as the Varieties of Financial Capitalism (VoFC) and it is a theoretical extension of the Varieties of Capitalism approach (VoC). It is the extension of the well-known political economy approach that was enriched with the “beyond VoC” view. In contrast to the initial approach, the VoFC approach sets as the structural actor in the core of its analytical framework the financial institution -which replaces the enterprise- reflecting, in this way, the vital importance of financial intermediation in the economy during the financial excess era. More particularly, the financial institution acts in an environment of strategic interaction with other structural actors and institutions of the capitalistic economy among which coordination is achieved. The varying nature of such coordination, based on a network of institutional complementarities, affects significantly the actors’ economic and productive efficiency of the respective capitalistic model. Consequently, the interactions among the actors in the subfields of financial intermediation and the institutional complementarities determine the nature of the achieved coordination, thus characterizing each VoFC. The empirical results point out a resilience of the nature of coordination as in most of the cases there is a continuity between the initial approach and VoFC, underlining that despite the evolution of capitalism during the era of financial excess the structural characteristics of the nature of coordination in each model have remained. Thus, (liberal) market-based coordination is detected to the market-centred financial systems, (strategic) cooperation-based coordination characterizes the bank-centred financial systems and state-led coordination is detected to the state(bank)-centred financial systems. This resilience of the nature of coordination also arises -to a significant extent- from the extension of the VoFC approach to the field of financial supervision that emerges from the versions of supervision of financial capitalism in Europe. Mainly, these versions of financial supervisory framework are (a) the traditional one that is detected in the state(bank)-centred financial systems, (b) the partially sophisticated one that is mostly located in the bank-centred financial systems, and (c) the sophisticated one which characterizes the market-centred financial systems. What is indicated from this kind of resilience -in an environment of evolving capitalism- is the difficulty of change for the fundamental characteristics of a political economy, while the types of coordination and the observed trends (before the 2007/2008 crisis) reflect the diachronic “conflict” between the state and the market forces for the “control” of economic activity. In the middle area of this fundamental competition lies the strategic cooperation of actors, balancing the trends of the two basic poles.Στην παρούσα διδακτορική διατριβή αναπτύσσεται μία προσέγγιση συγκριτικής ανάλυσης των ευρωπαϊκών συστημάτων καπιταλιστικής οργάνωσης υπό τα δεδομένα της φάσης χρηματοπιστωτικής υπερβολής της καπιταλιστικής οικονομίας. Φάση, κατά την οποία, πριν από το ξέσπασμα της κρίσης του 2007/2008 η χρέωση των δρώντων ήταν υπερδιπλάσια του παραγόμενου προϊόντος και το μέγεθος του χρηματοπιστωτικού συστήματος ήταν πενταπλάσιο της πραγματικής οικονομίας. Πρόκειται για την προσέγγιση των μοντέλων χρηματοπιστωτικής οργάνωσης, η οποία συνιστά την επέκταση της προσέγγισης των μοντέλων καπιταλιστικής οργάνωσης και δη της εμπλουτισμένης με τη «μία φάση πριν» εκδοχή της. Στον πυρήνα της, ως δομικός δρών κάθε μοντέλου, εντοπίζεται το χρηματοπιστωτικό ίδρυμα ως εκφραστής της ζωτικής για την καπιταλιστική οικονομία χρηματοπιστωτικής δραστηριότητας. Συγκεκριμένα, το χρηματοπιστωτικό ίδρυμα δρα σε ένα περιβάλλον στρατηγικής διάδρασης με τους άλλους δομικούς δρώντες και θεσμούς της καπιταλιστικής οικονομίας, με τους οποίους επιτυγχάνεται συγκεκριμένης φύσης συντονισμός που συνεισφέρει στην αποτελεσματικότητα της δραστηριότητας των δρώντων του συγκεκριμένου μοντέλου. Οι διαδράσεις, λοιπόν, που διαμορφώνονται μεταξύ των δρώντων σε υποπεδία της διαμεσολαβητικής δραστηριότητας, αλλά και στο πλαίσιο ενός πλέγματος «θεσμικών συμπληρωματικοτήτων», προσδιορίζουν τη φύση του συντονισμού που επιτυγχάνεται, προσδίδοντας «χαρακτήρα» στο μοντέλο χρηματοπιστωτικής οργάνωσης ανάλογα με τη φύση του συντονισμού. Τα αποτελέσματα της εμπειρικής διερεύνησης καταδεικνύουν την ανθεκτικότητα της φύσης του συντονισμού, καθώς παρατηρείται σε αρκετές περιπτώσεις μία ενδιαφέρουσα συνέχεια μεταξύ μοντέλων καπιταλιστικής οργάνωσης και μοντέλων χρηματοπιστωτικής οργάνωσης, υπογραμμίζοντας ότι, παρά την εξέλιξη -και μεταβολή- της φύσης της καπιταλιστικής οικονομίας, η φύση του συντονισμού διατηρεί τα δομικά χαρακτηριστικά της. Έτσι, εντοπίζονται ο συντονισμός με όρους δυνάμεων της αγοράς στα αγορακεντρικά συστήματα, ο συντονισμός με όρους στρατηγικής συνεργασίας των δρώντων της αγοράς στα τραπεζοκεντρικά συστήματα και ο συντονισμός με όρους παρέμβασης του κράτους στην αγορά στα κρατικοκεντρικά συστήματα. Η ανθεκτικότητα της φύσης του συντονισμού προκύπτει -σε σημαντικό βαθμό- και από την επέκταση της προσέγγισης των μοντέλων χρηματοπιστωτικής οργάνωσης στο πεδίο της εποπτείας της χρηματοπιστωτικής δραστηριότητας, όπως προκύπτει από την οπτική των εκδοχών εποπτείας της χρηματοπιστωτικής οργάνωσης. Πρόκειται, ειδικότερα, για τα παραδοσιακά εποπτικά πλαίσια που εντοπίζονται στα κρατικοκεντρικά συστήματα, τα μερικώς εξελιγμένα εποπτικά πλαίσια που χαρακτηρίζουν, κυρίως, τα τραπεζοκεντρικά συστήματα και τα εξελιγμένα εποπτικά πλαίσια των αγορακεντρικών συστημάτων. Αυτή, λοιπόν, η ανθεκτικότητα της φυσιογνωμίας του συντονισμού, έστω και με αποκλίσεις, μέσα σε ένα περιβάλλον καπιταλιστικής εξέλιξης, συνιστά σημαντική ένδειξη της δυσκολίας αλλαγής της φύσης μιας πολιτικής οικονομίας και δη των καταβολών της, ενώ οι τύποι του συντονισμού και οι σχετικές τάσεις αποτυπώνουν τη χρόνια «διαμάχη» για τον «έλεγχο» της οικονομικής δραστηριότητας ανάμεσα σε κράτος και αγορά, με τη στρατηγική συνεργασία των δρώντων να βρίσκεται στο μεσαίο χώρο αυτού του ιδιότυπου «ανταγωνισμού»