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In this study, a new EGR control technique, based on the estimate of the oxygen concentration in the intake manifold, was firstly investigated through numerical simulation and then experimentally tested, both under steady state and transient conditions. The robustness of the new control technique was also tested and compared with that of the conventional EGR control technique by means of both numerical simulation and experimental tests. Substantial reductions of the NOx emissions under transient operating conditions were achieved, and useful knowledge for controlling the EGR flow rate more accurately was obtained.

Different EGR system layouts (a Long Route, a Short Route, and a combination of the two) were evaluated by means of both numerical simulation and experimental tests. In particular, a one-dimensional fluid-dynamic engine model was built in order to evaluate the potential of a Long Route EGR system as well as the potential of different EGR combinations between Long and Short Route. By means of the one-dimensional model, used as a virtual test bench, the estimations of the NOx emissions, based on the Extended Zeldovich Mechanism (EZM), for the different solutions, were compared and valuable information for the calibration of the coordinated EGR LR, EGR SR and Variable Geometry Turbine (VGT) control systems was obtained.

Although the use of Exhaust Gas Recirculation (EGR) is nowadays mandatory for automotive diesel engines to achieve NOx emissions levels complying with more and more stringent legislation requirements, electronically controlled EGR systems still represent an expensive technology, often unsuitable for small diesel engines for off-road applications or for two/three wheelers. An interesting option for these categories of small diesel engines is the so-called “internal EGR”, which is obtained by modifying the intake or the exhaust valve lift profile, in order to increase the fraction of exhaust residuals at the end of the intake stroke. Different valve lift profiles were therefore evaluated for a 2 cylinders, 700 cc, Lombardini IDI diesel engine, equipping a light 4 wheelers vehicle.

A DoE analysis was carried out to investigate the effects of the compression ratio, injection timing, injector nozzle hole size and number on performance and emissions in a diesel marine engine, aiming to find out the optimal combination between all the abovementioned parameters. The study was performed on a six cylinder in line, 100 liter total displacement, diesel marine engine, by means of a 1-D engine simulation fluid-dynamic code, coupled with a multi-zone combustion model for oxide of nitrogen (NOx) and particulate (PM) prediction. A preliminary detailed validation process, based on an extensive experimental data set, was carried out on the engine model concerning, in particular, the predicted heat release rate, the in-cylinder pressure trace and NOx emissions for several operating points of a propeller load curve.

A new mean value engine model was developed in order to investigate the dynamic performance of vehicles equipped with turbocharged diesel engines, especially as far as the acceleration transients are concerned, where the turbolag phenomenon plays a major role. The turbocharger was modeled through the mass flow and efficiency maps which are usually provided by the manufacturer, with additional extrapolation routines for the map area in the low compression/expansion ratio region, which is particularly important for tip-in manoeuvres simulation. For the internal combustion engine modeling, experimentally derived maps of indicated efficiency, volumetric efficiency and exhaust gas temperature as a function of engine speed and load were used. Finally, a mass balance in the intake and exhaust manifolds was carried out with a filling and emptying technique.

Experimental Design methodologies have been applied in conjunction with objective functions for the optimization of the internal geometry of a rear muffler of a subcompact car equipped with a 1.4 liters displacement s.i. turbocharged engine. The muffler also features an innovative variable geometry design. The definition of an objective function summarising the silencing capability of the muffler has been driving the optimization process with the aim to reduce the tailpipe noise while maintaining acceptable pressure losses and complying with severe space constraints. Design of Experiments techniques for the reduction of experimental plans have been shown to be extremely effective to find out the optimum values of the design parameters, allowing a remarkable reduction of the time required by the design process in comparison with full factorial designs.

Different diagnostic techniques were experimentally tested on a common rail automotive 4 cylinder diesel engine in order to evaluate their capabilities to fulfill the California Air Resources Board (CARB) requirements concerning the monitoring of fuel injected quantity and timing. First, a comprehensive investigation on the sensitivity of pollutant emissions to fuel injection quantity and timing variations was carried out over 9 different engine operating points, representative of the FTP75 driving cycle: fuel injected quantity and injection timing were varied on a single cylinder at a time, until OBD thresholds were exceeded, while monitoring engine emissions, in-cylinder pressures and instantaneous crankshaft revolution speed.