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The effects of exhaust gas recirculation (EGR) cooling, in combination with a partially-premixed charge obtained by a very advanced fuel injection (early injection), on the combustion of a Common-Rail Diesel engine, have been experimentally investigated. The combustion behavior, for different injection strategies, has been analyzed as well as the emission levels. Experimental tests have been carried out on a direct injection Fiat 1929 cm3 Common Rail Diesel engine. Two different injection strategies have been investigated: the first one was obtained performing pilot and main injections only, the second one adding an early injection. The effects on engine combustion of hot and water cooled EGR have been compared with the combustion behavior without EGR, also showing the effect produced by different pilot injection timings and quantities.

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.

An axi-symmetric, five-hole V.C.O. nozzle mounted on an electro-injector was used to analyze the spray produced by each hole varying feeding pressure, injected quantity and timing. An advanced experimental apparatus has been used to investigate particle size and velocity of the sprays. The investigation comprized a hydraulic characterization, a photographic one with back-light technique, the analysis of the droplet size distribution through laser diffraction technique via MALVERN 2600 SERIES and the analysis of particle size and velocity using PDPA technique (AERMETRICS DSA 4000) with the extremely dense spray produced by the common-rail electronically controlled injection system. Four feeding pressures (25, 30, 90, 120 MPa) and five injected quantities (2, 4, 10, 25, 40 mm3/shot) were chosen to characterize the nozzle behavior. Sprays from different holes appeared different in shape but very similar in the droplet size distribution.

A simulation code of an innovative electro-injector for Diesel engines is presented with the preliminary analysis carried out using the code. The simulation code is based on the concentrated volume method. The energy and continuity conservation equations and dynamic equations are used for the movable parts of the system under friction. The one dimensional code simulated the propagation in the feeding pump and the control of the electro-injector. The program uses the method of characteristics to solve conservation equations, simulating the propagation in the pipe between the two chambers. To go deeply into the study of the electro-injector, main routine tests were carried out checking the exact value of diesel fuel parameters and the fuel energy losses with stationary and instationary flows. A comparison with different experimental results obtained by different types of electroinjectors, running at real conditions, has been made with good agreement.

The study of the spray of standard, five-hole, V.C.O. nozzles for D.I. diesel engine has been carried out. Several pictures of the spray have been taken using the back-light photography technique. Injected volume, feeding pressure, injection duration, spray penetration, angle and thickness, and flash delay from the start of injection have been measured both for nozzles of two different manufacturers and for a group of four injectors before and after a fatigue test of about 1500 hours running. Measurements revealed that each spray strongly depends on the needle lift, the back-pressure and the nozzle geometry and that, for the same injector, sprays are totally different from hole to hole. The causes of the most important differences have been attributed at the different hole inclination, their asymmetric feeding conditions (due to the eccentricity between needle and nozzle) and the microdefects caused by drilling operation.

A simulation code of an electro-injector for Diesel engines is presented with the preliminary parametric analysis carried out with the code. The simulation code is based upon the concentrated volume method as for the chambers of the system. Energy and flowrate conservation equations and dynamic equations are used for the movable parts of the system under stress or friction. The magnetic force acting on the electro-injector actuator has been calculated by means of a Finite Element simulation. The one-dimentional code simulated the propagation in feeding pipes and the control of the electro-injector. The program, infact, uses the method of the characteristic equations to solve conservation equations, simulating the propagation in a pipe between two chambers. The sensitivity analysis has pointed out that the parameters which are influenced by the propagation in the pipes are: needle lift, injected flow-rate, pressure in each chamber and volume.