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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.

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.

A 3-D analysis of the flow through a multihole, V.C.O. (Valve Covered Orifice) nozzle for D.I. Diesel Engine has been carried out. The analysis was performed by means of a finite element code. The nozzle comprises five injection holes. Aims of the analysis were: the investigation of the pressure drops along the conical clearance between the needle and the nozzle; the evaluation of the energy losses in the injection holes; the disclosure of the velocity profile at the injection hole outlets. the differences of flowrate for each hole with geometrical asymmetries. This kind of analisys is the first step of a more complete spray analysis; in fact, the spray from an injection hole is influenced by the injection pressure and the velocity profile. In particular, the needle lift and the needle tip deviation have been parametrized. The analysis betters both the theoretical knowledge of this kind of nozzle and the hydraulic phenomena occurring inside.

An analytical methodology to efficiently evaluate design alternatives in the conversion of a Common Rail Diesel engine to either CNG dedicated or dual fuel engine has been presented in a previous investigation. The simulation of the dual fuel combustion was performed with a modified version of the KIVA3V code including a modified version of the Shell model and a modified Characteristic Time Combustion model. In the present investigation, this methodology has been validated at two levels. The capability of the simulation code in predicting the emissions trends when changing pilot specification, like injected amount, injection pressure and start of injection, and engine configuration parameters, like compression ratio and axial position of the diesel injector has been verified. The second validation was related to the capability of the proposed computer-aided procedure in finding optimal solutions in a reduced computational time.