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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.

In order to study the effects of air bulk motion and methane injection strategies on the development and pollutant levels of dual-fuel combustion, an intense experimental campaign was performed on a diesel common rail research engine with variable inlet configurations. Activating only the swirl or the tumble inlet valve of the engine, or both of them, it was possible to obtain, inside the cylinder, three different bulk flow structures. The air-methane mixture was obtained injecting the gaseous fuel into the inlet manifold varying its pressure and the injector position, either very close to the inlet valves, in order to obtain a stratified-like mixture, or more upstream, to obtain a homogeneous-like mixture. By combining the two different positions of the injector and the three air bulk flow structures, seven different inlet setup have been tested, at different values of engine speed and load.

The aim of the present investigation is the implementation of an innovative procedure to optimise the design of a high pressure common rail electro-injector. The optimization method is based on the use of genetic programming, a search procedure developed by John Holland at the University of Michigan. A genetic algorithm (GA) creates a random population which evolves combining the genetic code of the most capable individual of the previous generation. For the present investigation an algorithm which includes the operators of crossover, mutation and elitist reproduction has been developed. This genetic algorithm allows the optimization of both single and multicriteria problems. For the determination of the multi-objective fitness function, the concept of Pareto optimality has been implemented. The performance of the multiobjective genetic algorithm was examined by using appropriate mathematical functions and was compared with the single objective one.

Modeling autoignition in diesel engines is a challenging task because of the wide range of equivalence ratios over which it takes place. A variety of detailed autoignition models has been proposed in literature for different fuels. Since these models include about one thousand chemical reactions and more than one hundred species, their application to CFD engines simulations requires a very high computational time, so that they are of no practical interest. In order to lower the computational time, a number of reduced models has been developed including the shell model, which is one of the most used. This model does not take into account low temperature kinetics and consists of seven reactions and three radicals. The use of this model in engine simulations shows its limits when applied to delayed injections because of the predominant influence of the low temperature kinetics. A modified version of the shell model is proposed in the present study.

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 optimization procedure adopted in the present investigation is based on Genetic Algorithms (GA) and allows different fitness functions to be simultaneously maximized. The parameters to be optimized are related to the geometric features of the combustion chamber, which ranges of variation are very wide. For all the investigated configurations, bowl volume and squish-to-bowl volume ratio were kept constant so that the compression ratio was the same for all investigated chambers. This condition assures that changes in the emissions were caused by geometric variations only. The spray injection angle was also considered as a variable parameter. The optimization was simultaneously performed for different engine operating conditions, i.e. load and speed, and the corresponding fitness values were weighted according to their occurrence in the European Driving Test.

In the present study, the influence of pressure waves propagating in the ducts of common rail injection systems on engine out emission has been investigated. The pressure waves originated by the closure of the injectors are characterized by an amplitude that can easily be greater than 10 MPa. When a multi injection strategy is adopted such fluctuations can strongly affect fuel delivery rate of subsequent injections and therefore emission levels and fuel consumption. The paper reports the results of an experimental investigation that has been carried out on a single cylinder engine equipped with a common rail electronically controlled high pressure injection system and an optical access, via endoscopes, for the visualization of soot and combustion process. The used injection strategy consisted of pilot and main injection. To allow the start of the main injection on a local pressure peak or valley without changing injection timing, injection system ducts of different length were used.

This investigation describes the results of an experimental and numerical research project aimed at comparing mileage and CO2 emissions from two different commercial versions of Daimler AG Smart ForTwo car: conventional (gasoline) and electric (ED). The investigation includes numerical simulations with the AVL CRUISE software package and on-board acquisitions. A data acquisition system has been designed for this purpose and assembled on board of the Smart ED. The system is composed by a GPS antenna with USB interface, two current transducers, a NI-DAQ device and a netbook computer with a LabView-VI. This system provided on-board information about driving cycle and current flows, gathered simultaneously by GPS, transducers and NI-DAQ. The system was also used to evaluate the losses of energy during the recharge of the electric car. The two cars have been tested over a wide range of driving conditions related to different routes, traffic conditions and use of on-board accessories (i.e.

The present study focuses on the causes of dissimilarity in the flow structures of sprays produced by different holes of the same direct injection high-pressure diesel nozzle. To assess the effect of nozzle geometry on the transient spray structure, photographs of the spray plumes produced by VCO, mini-sac and reduced sac nozzles at different delays from the start of injection were acquired. Injected fuel volume, feeding pressure, injection duration, spray penetration and cone angle were measured for all the investigated nozzles. A statistical analysis of the acquired images and data showed that sprays from the same hole were highly repeatable even with clear hole-to-hole variation of the spray structure. In particular, for the three investigated nozzle geometries the effect of nozzle flow rate, hole inlet and outlet diameter, needle geometry and working time under engine conditions were investigated. Microscope pictures of the nozzle holes were also acquired.