Automotive diesel engine transient operation: modeling, optimization and control

Traditionally, the study of internal combustion engines operation has focused on the steady-state performance. However, the daily driving schedule of automotive engines is inherently related to unsteady conditions. There are various operating conditions experienced by (diesel) engines that can be classified as transient. Besides the variation of the engine operating point, in terms of engine speed and torque, also the warm up phase can be considered as a transient condition. Chapter 2 has to do with this thermal transient condition; more precisely the main issue is the performance of a Selective Catalytic Reduction (SCR) system during cold start and warm up phases of the engine. The proposal of the underlying work is to investigate and identify optimal exhaust line heating strategies, to provide a fast activation of the catalytic reactions on SCR. Chapters 3 and 4 focus the attention on the dynamic behavior of the engine, when considering typical driving conditions. The common approach to dynamic optimization involves the solution of a single optimal-control problem. However, this approach requires the availability of models that are valid throughout the whole engine operating range and actuator ranges. In addition, the result of the optimization is meaningful only if the model is very accurate. Chapter 3 proposes a methodology to circumvent those demanding requirements: an iteration between transient measurements to refine a purpose-built model and a dynamic optimization which is constrained to the model validity region. Moreover all numerical methods required to implement this procedure are presented. Chapter 4 proposes an approach to derive a transient feedforward control system in an automated way. It relies on optimal control theory to solve a dynamic optimization problem for fast transients. From the optimal solutions, the relevant information is extracted and stored in maps spanned by the engine speed and the torque gradient.

Structural verification of the ESEO spacecraft: from launch loads analysis to composite panels verification

The present thesis work was performed in the frame of ESEO (European Student Earth Orbiter) project. The activities that are described in this document were carried out in the Microsatellites and Space Micro systems Lab led by Professor Paolo Tortora and in ALMASpace company facilities. The thesis deals with ESEO structural analysis, at system and unit level, and verification: after determining the design limit loads to be applied to the spacecraft as an envelope of different launchers load profiles, a finite element structural analysis was performed on the model of the satellite in order to ensure the capability to withstand the loads encountered during the launch; all the analyses were performed according to ESA standards and using the software MSC NASTRAN SIMXPERT. Amplification factors were derived and used to determine loads to be considered at unit level. In particular structural analyses were carried out on the GPS unit, the payload developed for ESEO by students of University of Bologna and results were used in the preparation of GPS payload design definition file. As for the verification phase a study on the panels and inserts to be used in the spacecraft was performed: different designs were created exploiting methods to optimize weight and mechanical behavior. The configurations have been analyzed and results compared to select the final design.

Direct and inverse transient eddy current problems

Die vorliegende Arbeit behandelt Vorwärts- sowie Rückwärtstheorie transienter Wirbelstromprobleme. Transiente Anregungsströme induzieren elektromagnetische Felder, welche sogenannte Wirbelströme in leitfähigen Objekten erzeugen. Im Falle von sich langsam ändernden Feldern kann diese Wechselwirkung durch die Wirbelstromgleichung, einer Approximation an die Maxwell-Gleichungen, beschrieben werden. Diese ist eine lineare partielle Differentialgleichung mit nicht-glatten Koeffizientenfunktionen von gemischt parabolisch-elliptischem Typ. Das Vorwärtsproblem besteht darin, zu gegebener Anregung sowie den umgebungsbeschreibenden Koeffizientenfunktionen das elektrische Feld als distributionelle Lösung der Gleichung zu bestimmen. Umgekehrt können die Felder mit Messspulen gemessen werden. Das Ziel des Rückwärtsproblems ist es, aus diesen Messungen Informationen über leitfähige Objekte, also über die Koeffizientenfunktion, die diese beschreibt, zu gewinnen. In dieser Arbeit wird eine variationelle Lösungstheorie vorgestellt und die Wohlgestelltheit der Gleichung diskutiert. Darauf aufbauend wird das Verhalten der Lösung für verschwindende Leitfähigkeit studiert und die Linearisierbarkeit der Gleichung ohne leitfähiges Objekt in Richtung des Auftauchens eines leitfähigen Objektes gezeigt. Zur Regularisierung der Gleichung werden Modifikationen vorgeschlagen, welche ein voll parabolisches bzw. elliptisches Problem liefern. Diese werden verifiziert, indem die Konvergenz der Lösungen gezeigt wird. Zuletzt wird gezeigt, dass unter der Annahme von sonst homogenen Umgebungsparametern leitfähige Objekte eindeutig durch die Messungen lokalisiert werden können. Hierzu werden die Linear Sampling Methode sowie die Faktorisierungsmethode angewendet.

The effect of the ductility on the collapse loads: The failure of a steel roof

Studio dell'effetto della duttilità sul carico di collasso: il crollo di una copertura reticolare spaziale in acciaio causato dalla compresenza di un'ingente mancanza di resistenza e duttilità nei collegamenti delle aste e possibili stati coattivi. Il carico di collasso nel caso di strutture a bassa duttilità dipende dalla presenza di stati coattivi dovuti a imperfezioni di realizzazione o cedimenti vincolari della struttura in esercizio.

Development of Dynamic Constraint Models for a Model Based Transient Calibration Process

Model based calibration has gained popularity in recent years as a method to optimize increasingly complex engine systems. However virtually all model based techniques are applied to steady state calibration. Transient calibration is by and large an emerging technology. An important piece of any transient calibration process is the ability to constrain the optimizer to treat the problem as a dynamic one and not as a quasi-static process. The optimized air-handling parameters corresponding to any instant of time must be achievable in a transient sense; this in turn depends on the trajectory of the same parameters over previous time instances. In this work dynamic constraint models have been proposed to translate commanded to actually achieved air-handling parameters. These models enable the optimization to be realistic in a transient sense. The air handling system has been treated as a linear second order system with PD control. Parameters for this second order system have been extracted from real transient data. The model has been shown to be the best choice relative to a list of appropriate candidates such as neural networks and first order models. The selected second order model was used in conjunction with transient emission models to predict emissions over the FTP cycle. It has been shown that emission predictions based on air-handing parameters predicted by the dynamic constraint model do not differ significantly from corresponding emissions based on measured air-handling parameters.

Development of a model-based transient calibration process for diesel engine electronic control module tables – Part 1: data requirements, processing, and analysis

This is the first part of a study investigating a model-based transient calibration process for diesel engines. The motivation is to populate hundreds of parameters (which can be calibrated) in a methodical and optimum manner by using model-based optimization in conjunction with the manual process so that, relative to the manual process used by itself, a significant improvement in transient emissions and fuel consumption and a sizable reduction in calibration time and test cell requirements is achieved. Empirical transient modelling and optimization has been addressed in the second part of this work, while the required data for model training and generalization are the focus of the current work. Transient and steady-state data from a turbocharged multicylinder diesel engine have been examined from a model training perspective. A single-cylinder engine with external air-handling has been used to expand the steady-state data to encompass transient parameter space. Based on comparative model performance and differences in the non-parametric space, primarily driven by a high engine difference between exhaust and intake manifold pressures (ΔP) during transients, it has been recommended that transient emission models should be trained with transient training data. It has been shown that electronic control module (ECM) estimates of transient charge flow and the exhaust gas recirculation (EGR) fraction cannot be accurate at the high engine ΔP frequently encountered during transient operation, and that such estimates do not account for cylinder-to-cylinder variation. The effects of high engine ΔP must therefore be incorporated empirically by using transient data generated from a spectrum of transient calibrations. Specific recommendations on how to choose such calibrations, how many data to acquire, and how to specify transient segments for data acquisition have been made. Methods to process transient data to account for transport delays and sensor lags have been developed. The processed data have then been visualized using statistical means to understand transient emission formation. Two modes of transient opacity formation have been observed and described. The first mode is driven by high engine ΔP and low fresh air flowrates, while the second mode is driven by high engine ΔP and high EGR flowrates. The EGR fraction is inaccurately estimated at both modes, while EGR distribution has been shown to be present but unaccounted for by the ECM. The two modes and associated phenomena are essential to understanding why transient emission models are calibration dependent and furthermore how to choose training data that will result in good model generalization.

Development of a model-based transient calibration process for diesel engine electronic control module tables – Part 2: modelling and optimization

This is the second part of a study investigating a model-based transient calibration process for diesel engines. The first part addressed the data requirements and data processing required for empirical transient emission and torque models. The current work focuses on modelling and optimization. The unexpected result of this investigation is that when trained on transient data, simple regression models perform better than more powerful methods such as neural networks or localized regression. This result has been attributed to extrapolation over data that have estimated rather than measured transient air-handling parameters. The challenges of detecting and preventing extrapolation using statistical methods that work well with steady-state data have been explained. The concept of constraining the distribution of statistical leverage relative to the distribution of the starting solution to prevent extrapolation during the optimization process has been proposed and demonstrated. Separate from the issue of extrapolation is preventing the search from being quasi-static. Second-order linear dynamic constraint models have been proposed to prevent the search from returning solutions that are feasible if each point were run at steady state, but which are unrealistic in a transient sense. Dynamic constraint models translate commanded parameters to actually achieved parameters that then feed into the transient emission and torque models. Combined model inaccuracies have been used to adjust the optimized solutions. To frame the optimization problem within reasonable dimensionality, the coefficients of commanded surfaces that approximate engine tables are adjusted during search iterations, each of which involves simulating the entire transient cycle. The resulting strategy, different from the corresponding manual calibration strategy and resulting in lower emissions and efficiency, is intended to improve rather than replace the manual calibration process.

Reduction of Transient Particulate Matter Spikes with Decision Tree Based Control

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

Early antiretroviral therapy during primary HIV-1 infection results in a transient reduction of the viral setpoint upon treatment interruption

Long-term benefits of combination antiretroviral therapy (cART) initiation during primary HIV-1 infection are debated.

Elevated bilirubin in acute and transient psychotic disorder

Mild unconjugated hyperbilirubinemia seems to be more common in patients with disorders from the schizophrenic spectrum than in other psychiatric patients or in the general population and has been linked to brain alterations. This spectrum however contains a number of diagnostic entities that might not share the same etiological and environmental factors.

Insight into the mechanism of transient trapping in micellar electrokinetic chromatography

Transient trapping is a new mechanism of on-line sample concentration and separation that has recently been presented. It involves the injection of a short length of micellar solution in front of the sample, making it similar to sweeping in partial-filling MEKC. Here, we examine the mechanism of transient trapping by the use of computer simulations and compare it to sweeping in MEKC for the two analytes, sulforhodamine B and 101. The simulation results confirm the mechanism for concentration and separation originally proposed. The mechanism for concentration is similar to sweeping since the analytes are picked and accumulated by the micelles that penetrate the sample zone. The mechanism for separation is however quite unique since the concentrated analytes are trapped for a few seconds on the sample/micelle boundary before they are released as the concentration of micelle is reduced as it undergoes electromigration dispersion and the analytes separate down a micelle gradient. Simulation results suggested that a significant contribution of band broadening arises from the micelle gradient, with shallower gradients resulting in broader peaks. However, this is offset by an increase in selectivity, such that resolution was enhanced even though the peaks are broader. Transient trapping analysis with similar resolution to those obtained by sweeping MEKC could be achieved in 1/10 of the time and 1/4 of the capillary length, which results in a 2-3 times increase in sensitivity.

Copeptin and risk stratification in patients with ischemic stroke and transient ischemic attack: The CoRisk Study

RATIONALE: Copeptin independently predicts functional outcome and mortality at 90 days and one-year after ischemic stroke. In patients with transient ischemic attack, elevated copeptin values indicate an increased risk of further cerebrovascular events. AIMS: The Copeptin Risk Stratification (CoRisk) study aims to validate the predictive value of copeptin in patients with ischemic stroke and transient ischemic attack. In patients with ischemic stroke, the CoRisk study aims to further explore the effect of treatment (i.e. thrombolysis) on the predictive value of copeptin. DESIGN: Prospective observational multicenter study analyzing three groups of patients, i.e. patients with ischemic stroke treated with and without thrombolysis and patients with transient ischemic attack. OUTCOMES: Primary end-point: In patients with ischemic stroke, the primary end-point includes disability (modified Rankin scale from 3 to 5) and mortality (modified Rankin scale 6) at three-months after stroke. In patients with transient ischemic attack, the primary end-point is a recurrent ischemic cerebrovascular event (i.e. ischemic stroke or recurrent transient ischemic attack). Secondary end-point: In patients with ischemic stroke, the secondary end-points include in-house complications (i.e. symptomatic intracerebral hemorrhage, malignant edema, aspiration pneumonia or seizures during hospitalization, and in-house mortality).