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The design of a hybrid electric powertrain requires a complex optimization procedure because its performance will strongly depend on both the size of the components and the energy management strategy. The problem is particular critical in the aircraft field because of the strong constraints to be fulfilled (in particular in terms of weight and volume). The problem was addressed in the present investigation by linking an in-house simulation code for hybrid electric aircraft with a commercial many-objective optimization software. The design variables include the size of engine and electric motor, the specification of the battery (typology, nominal capacity, bus voltage), the cooling method of the motor and the battery management strategy. Several key performance indexes were suggested by the industrial partner. The four most important indexes were used as fitness functions: electric endurance, fuel consumption, take-off distance and powertrain volume.

The present study aims at the implementation of a Matlab/Simulink environment to assess the performance (thrust, specific fuel consumption, aircraft/engine mass, cost, etc.) and environmental impact (greenhouse and pollutant emissions) of conventional and more electric aircrafts. In particular, the benefits of adopting more electric solutions for either aircrafts at given missions specifications can be evaluated. The software, named PLA.N.E.S, includes a design workflow for the input of aircraft specification, kind of architecture (e.g. series or parallel) and for the definition of each component including energy converter (piston engine, turboprop, turbojet, fuel cell, etc.), energy storage system (batteries, super-capacitors), auxiliaries and secondary power systems. It is also possible to setup different energy management strategies for the optimal control of the energy flows among engine, secondary equipment and storage systems during the mission.

This paper deals with numerical investigations concerning the working behavior of a hydraulic impact machine. Attention is focused on the moving elements inside the casing of the breaker, taking the main targets to be achieved by the designer into account. On one hand, there is the operating performance optimization, with particular care devoted to the impact energy of the breaker; on the other hand, the energy conversion efficiency, related to the power transmission, in order to minimize the power requirement to the feeding system. Use of a parameterized numerical model is made in order to better understand the effects of parameters characteristic of distributor and striking mass on breaker performance and to achieve possible improvements in both impact energy and efficiency. The key-variable, which leads to better performance, is found to be the working pressure.

Percussive breaking is basically a process in which short duration blows with high force intensity are applied in rapid succession, resulting in rock, concrete or pavement fragmentation. The machine for such a task is the hydraulic breaker which turns the hydraulic energy supplied by a positive displacement pump into mechanical energy as percussions of a piston against a chisel. This work presents the results of experimental tests carried out on a hydraulic breaker to determine its blow impact energy. Then, using these data, theoretical considerations are formulated in order to understand the phenomenon of the tool loading especially at the instant of the impact of the piston against the chisel, leading to the energy release.

The present work deals with tests on a DI Diesel engine equipped with two different types of Common Rail injectors, the second one allowing a “smoother” fuel rate in the first stage of injection. The work aims at understanding how injection parameters and different injection rates may affect the combustion process in terms of in-cylinder pressure, noise and vibrations of the engine block. The tests performed for the same engine torque generally showed that engine speed, injection pressure and pilot injection duration are the most significant parameters that affect engine noise emissions. As regards the injection rate modulation, experiments showed that it is possible to reduce combustion noise at low engine speeds if the initial rate of injection is lower during the first stage of injection.

The aim of the present work is to evaluate the influence of the pilot injection on combustion of a TDI Diesel engine for different engine torque and speed conditions. For this investigation, pilot injection timing and duration were varied on a wide range of values, and their effects on combustion pressure, rate of heat release, pilot and main combustion delay, combustion process and exhaust emissions in terms of NOx and smoke were analyzed. An in-line, four-cylinder, turbocharged FIAT 1930 cm3 TDI Diesel engine, equipped with Common Rail injection system, was tested. A piezoelectric sensor was located in the combustion chamber in order to acquire combustion pressure; from these signals, gross heat release rate was derived in order to analyze the combustion behavior. Pollutant emission levels have been measured by means of a gas analyzer, while for smoke an opacimeter was used.

The influence of some injection parameters (as main injection timing, pilot injection timing, pilot injection duration) on noise emissions and combustion noise level of a Diesel engine has been evaluated. The noise emissions of an in-line, four cylinder, turbocharged FIAT 1929 cm3 TDI engine were measured using an ambient microphone and accelerometers. The injection system of the engine used was the high-pressure Common Rail system. The experimental results were elaborated using an ANOVA (analysis of variance) technique, to evaluate the influence of the control parameters on the controlled ones. Moreover, a multi-layer neural network was used to predict noise emissions and vibration level. It was found that the accelerometer mounted on the top of the engine bolt, which clamped the head of the cylinder to the crankcase, gave the best coherence of the results.

Shaping the injection rate in Diesel engines influences combustion and emissions. Fluid-dynamic steady-state characteristics and transient response of the control valve of high-pressure, electronically controlled, injection systems are important factors for the control of the shape, duration and timing of the injection, especially during pilot injections. Computed results, obtained using a model to predict the cavitation behavior of the control valve of a high-pressure fuel injection system for Diesel engine, are presented. The numerical investigation has been made using different cavitation models, involving the hypothesis of a barotropic cavitation, or fluid dynamic model with non-equilibrium cavitation modeling. As a result, the computed mass flow values were compared with the experimental data. Calculations have been performed to investigate the influence of the transient development of the cavitation.

An existing simulation code of a COMMON RAIL Diesel fuel injector, named UNIJET, has been revised and completed, with the aim to predict injection characteristics and to investigate on the instabilities which appeared in experimental tests. Particular attention has been given to the injector control valve modeling, to understand the influence of cavitation on discharge flow characteristics. The valve residual motion, after a Pilot Injection cycle, is responsible for the clear and sudden injected quantity variations of subsequent Master injection, as the time delay between the two cycles decreases. Numerical predictions have been compared with valve lift measurements, and with experimental relation among fuel injected quantity, injection pressure and duration.