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The effect of external EGR on knock was evaluated using a CFR engine. Combustion pressure was sampled on a time basis. A band pass filter in the time domain was applied to the pressure cycles. Five knock indices were calculated for each combustion cycle. The problem to quantify knock intensity was focused. At this extent measurements were carried out on standard isooctane-n-heptane blends in the test conditions used for the determination of the Motor Method Octane Number (MON). Knock intensity was varied acting on compression ratio. For each index, the conditions of absence of knock were determined using motored cycles. The indices were compared and one of them, showing the lowest C.O.V., was selected for further measurements. The effect of EGR on test fuels having different composition was evaluated varying the compression ratio, at fixed ignition timing. In this way, the same level of detonation, obtained in the absence of EGR, was realized with different amount of external EGR.

An experimental and numerical investigation, using the Laser Doppler Anemometry (LDA) technique and a 3D fluid-dynamic code (KIVA 3V), was carried out in a prototype engine under steady-state conditions. The aim of the present activity was the flow field characterization and the effect of the intake geometry on the in-cylinder tumble flow. A new steady flow test rig designed for capturing the tumble motion within a test cylinder, made by a blower and an engine head, was assembled to simulate the intake flow. The engine head was mounted on an aluminum cylinder, having the same bore as the real engine. The cylinder was provided with optical accesses on the periphery and a flat optical window located at the bottom to a depth equal to the stroke of the engine. The cylinder was also equipped with two cylindrical ducts, used as air outflow ports.

Multidimensional computations of homogeneous charge spark ignition engines were made with the KIVA II code. Combustion was simulated using the Fractal Flame Model of Zhao [5]. The original code was modified to obtain better calculations of heat transfer and to take into account the mass flow in the crevices. The predictions were compared with measurements carried out on a CFR engine. The tests were carried out in stoichiometric condition with isooctane. Compression ratio, ignition timing and EGR level were selected as test parameters. The global agreement between calculations and experiments was evaluated on the basis of heat release, indicated pressure patterns and pollutants measurements. For the lower compression ratio (7.7) the predictions of pressure cycle generally were in good agreement with experiments. However the empirical constant used in this condition cannot be used at higher compression ratio to obtain acceptable predictions of the pressure cycle.

A simple model of combustion and pollutant formation has been set up. It is part of an engine simulator to be used for the study of engine control strategies. The calculation of inlet and exhaust phases is performed by an emptying and filling method, based on the knowledge of mean inlet and exhaust conditions. A single zone thermodynamic model has been utilized for the calculation of the combustion phase. The values of the shape factors of heat release patterns have been modeled to take into account air/fuel ratio, EGR, load and turbulence at ignition starting. Crevice storage of unburned mixture has been considered as the dominant mechanism for unburned HC production. A model for mixing and burning of HC inside the cylinder has been proposed. NO is calculated using the three steps Zeldovich approach. The model produces realistic calculations of combustion pressure and pollutants emission at various speed, load, ignition timing and EGR.