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Development through Simulation of a Turbocharged 2-Stroke G.D.I. Engine Focused on a Range-Extender Application
No full textAn original 2-stroke prototype engine, equipped with an electronically controlled gasoline direct-injection apparatus, has been tested over the last few years, and the performances of these tests have been compared with those obtained using a commercial crankcase-scavenged 2-stroke engine. Very satisfactory results have been obtained, as far as fuel consumption and unburned hydrocarbons in the exhaust gas are concerned. Large reductions in fuel consumption and in unburned hydrocarbons have been made possible, because the injection timing causes all the injected gasoline to remain in the combustion chamber, and thus to take part in the combustion process. Moreover, a force-feed lubrication system, like those usually exploited in mass-produced 4-stroke engines, has been employed, because of the presence of an external pump. In fact, it is no longer necessary to add oil to the gasoline in the engine, as the gasoline does not pass through the crankcase volume. The aim of this paper is to present the main features of a new 2-stroke engine, which mainly pertain to the adoption of a turbo compressor for the scavenging and supercharging processes, as well as a small volumetric impeller for the start transitory. Because of its limited size, weight and high specific power output, this engine should be of particular interest for range extender applications in electric vehicles. A numerical simulation has been carried out, to confirm results of the experimental phase, by means of a one-dimensional model that has furnished encouraging results
Modeling of surface roughness in electro-discharge machining using artificial neural networks
No full textElectro-Discharge machining (EDM) is a thermal process comprising a complex metal removal mechanism. This method works by forming of a plasma channel between the tool and the workpiece electrodes leading to the melting and evaporation of the material to be removed. EDM is considered especially suitable for machining complex contours with high accuracy, as well as for materials that are not amenable to conventional removal methods. However, several phenomena can arise and adversely affect the surface integrity of EDMed workpieces. These have to be taken into account and studied in order to optimize the process. Recently, artificial neural networks (ANN) have emerged as a novel modeling technique that can provide reliable results and readily, be integrated into several technological areas. In this paper, we use an ANN, namely, the multi-layer perceptron and the back propagation network (BPNN) to predict the mean surface roughness of electro-discharge machined surfaces. The comparison of the derived results with experimental findings demonstrates the promising potential of using back propagation neural networks (BPNNs) for getting a reliable and robust approximation of the Surface Roughness of Electro-discharge Machined Components
Mild Hybrid Electric Vehicles: Powertrain Optimization for Energy Consumption, Driveability and Vehicle Dynamics Enhancements
No full textThis thesis deals with the modeling, the design and the control of mild hybrid electric vehicles. The main goal is to develop accurate design tools and methodologies for preliminary system and component level analysis. Particular attention is devoted to the configuration in which an electric machine is mounted on the rear axle of a passenger car. The use of such a machine in parallel with the internal combustion engine allows one to exploit different functionalities that are able to reduce the overall fuel consumption of the vehicle. In addition, the indirect coupling between the thermal and the electric machine, realized through the road and not by means of mechanical couplers, together with the position of the latter in the overall vehicle chassis system, enables such an architecture to be efficient both from the energy recovery and the full electric driving point of view. Chapter 1 introduces the problem of fuel consumption and emissions reduction in the overall world context and presents the main hybrid architectures available. Chapter 2 is devoted to the study of the influence of the electric machine position in the powertrain regarding the regenerative braking potentialities concerned. The model considered for the analysis will be described on each of its subcomponents. The braking performance of the vehicle in electric mode is presented considering no losses in the electric powertrain (electric motor, battery, inverter). Chapter 3 is dedicated to the design of an electric machine for a rear axle powertrain. The specifications of such machine are optimized considering both the vehicle and the application under analysis. The design takes into account analytical techniques for the computation of electrical parameters (such as phase and DC currents) and the torque - speed map, as well as numerical ones for its thermal behavior. In Chapter 4 the electrical and thermal characteristics of the designed electric motor are implemented in the model presented in Chapter 2. The overall vehicle model is therefore used both to assess a simple torque split strategy between thermal and electric machine and to perform an optimal sizing of the battery considering all the limitations imposed by the electric powertrain (e. g. maximum currents, maximum temperatures). Chapter 5 makes a step forward and analyzes the different implications that the use of the rear axle electric motor to brake the vehicle has on the vehicle dynamics. Open loop analysis will present a degradation of the vehicle handling comfort caused by the introduction of an oversteering moment to the vehicle. Through the use of a simplified vehicle model, the introduced oversteering yaw moment is evaluated, while a control strategy based on a new stability detector will show how to find a trade off between handling comfort and regenerable energy. At last, Chapter 6 deals with the problem of longitudinal driving comfort. Drivelines and chassis are lightly damped systems and the application of an impulsive torque imposed by the driver can cause the vehicle longitudinal acceleration (directly perceived by the driver) to be oscillating and non smooth. A sensitivity analysis on a conventional powertrain is presented demonstrating which of the different components are more influential in the different modes of vibration, and possible solutions to improve the driveability are proposed. One of these relates to the use of the rear axle electric machine in order to give more responsiveness to the vehicle. Finally, concluding remarks are given in Chapter 7
Low-E paints enhanced building components: Performance, limits and research perspectives
No full textIn the latest years, different solutions have been developed in order to increase the energy performance of opaque building envelopes as far as the heat losses are concerned. Most of them are mainly focused on the bulk properties of materials and are aimed at reaching very low values of thermal conductivity, i.e., super insulating materials. Contemporarily research has been carried out aimed at exploiting the low emissivity in order to reduce the radiative heat transfer between surfaces separated by cavities and, if applied as an internal coating, in order to increase the indoor thermal comfort. In this paper, several solutions that have been experimentally investigated in the latest two years by the authors are presented
Integrated Sensors & Read-Out: simulations, design and tests for highly advanced applications, from Robotics to High Energy Physics
No full textThis thesis presents design, simulations and tests of Silicon CMOS and Bi-CMOS sensors and read-out circuits for robotic and high energy physics applications. The project is divided in two main sub-parts: • Design, analysis, simulations, layout and tests of integrated sensors and electronic read-out circuits. Integrated temperature sensor and reference were designed for biomedical applications, while two read-out circuits were conceived to interface pressure sensors in robotic applications, more specifically hand exoskeletons and robotic tactile skin. • Physics performance studies of the Pixel detectors of the ATLAS experiment at CERN, as an example of advanced silicon device for ionizing particle detection. The fist Chapters of this thesis intend to show that even if most robotic applications prefer to rely on commercially available ICs to read-out tactile information, a custom solution can be even more effective as it offers some crucial advantages. For instance, human response to touch has a complex dynamics which is very difficult to be faithfully replicated at robotic-level with a general-purpose block, such as a microcontroller. On the contrary, custom solutions offer a much higher flexibility to reproduce human physiology at robotic level, without compromising the system modularity. The presented read-out circuits feature the crucial advantage of tunable output sensitivity, low-power consumption and compact size. Furthermore,they are designed with logic blocks only, to be modularly replicated and possibly implemented in different technologies with low efforts. The analog-to-digital conversion was achieved through a voltage-to-frequency conversion, which is an effective technique to partially attenuate the dramatic consequences of scaling in purely analog design. The read-out circuit for tactile skin has the major advantage of robustness with respect to process, voltage and temperature variations, which makes the solution even more attractive for the read-out of robotic systems. The interface for hand exoskeleton presents the important feature of providing both contact detection and pressure evaluation. The thesis details all steps carried out by the candidate, from the transistor-level design, through the simulations and layout to the electrical measurements, which allow to test the performance of the read-out circuit couple with the sensor. The temperature sensor and reference were designed in Bi-CMOS technology and exploited a bandgap architecture to take advantage of the linear dependence of bipolar transistor base-emitter voltage with absolute temperature. These ICs are still under development, hence only design and simulations are provided. Nevertheless, knowledge gained from the analog design (e.g., temperature dependence of integrated capacitors) was later used for the performance analysis of the pixel sensor of the IBL sub-detector. Experience achieved from design of integrated sensors and electronic interfaces offers peculiar expertise to analyze the performance of pixel sensors for particle Physics applications in terms of charge collection properties. The pixel integrated sensor and read-out circuit was studied in detail thanks to the expertise gained by designing the previously presented ICs. Specifically, it was demonstrated that effects in the read-out system (e.g., quantization resolution, electronic noise, radiation damage of the sensitive substrate) play an important role in defining the sensor performance, hence dramatically affect the tracking performance of the overall LHC. The pixel performance was studied in terms of charge calibration, spatial resolution optimization and two track separation. This analysis was performed using both custom simulations of charge collection phenomena (occurring at the sensor and read-out level) and official ATLAS Monte Carlo simulation software. The results were successfully compared to ATLAS collision data and result of dedicated Beam Test