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The possibility to mitigate the knock onset by means of a controlled coolant flow rate is investigated. The study is carried out on a small displacement, N.A. 4-valve per cylinder SI engine. The substitution of the standard belt-driven pump with an electrically driven one allows the variation of the coolant flow rate regardless of engine speed and permits, therefore, the adoption of a controlled coolant flow rate. The first set of experimental tests aims at evaluating the engine operating condition and the coolant flow rate, which are more favorable to the knock onset. Starting from this condition, subsequent experimental tests are carried out for transient engine operating conditions, by varying the coolant flow rates and evaluating, therefore, its effects on cylinder pressure fluctuations. In all the experiments, the spark advance and the equivalence ratio are controlled by the ECU according to the production engine map.

The paper illustrates a zero-dimensional dynamic model which was developed in the MATLAB®/Simulink environment to predict thermal transient of an automotive cooling system. In particular, the rapid switch-off of an internal combustion engine which was operated for a prolonged time at high speed under full load was investigated. In this condition, significant vapour formation and, consequently, pressure rise within the cooling circuit can arise, because of the sudden heat transfer from the high temperature head metal to the coolant contained in the cylinder head passages. The proposed model allows predictions of the vaporized mass of coolant as well as of the pressure evolution within the cooling circuit. The simulations results were compared with experimental tests carried out on a production 4-cylinder, MPI small S.I. engine, 1.2 dm3 displacement, and the agreement was very satisfactory.

The fluid dynamic behavior of four-valve high performance engines were investigated at the steady flow rig. In particular, the intake phase was considered. A global characterization was performed using the discharge coefficient, while the Laser Doppler Anemometry (LDA) technique was adopted to define the flow field around the intake valves. The purpose of the paper is to evaluate the influence of the valve-to-wall clearance on the flow distribution inside the combustion chamber. The analysis showed that, at low valve-to-wall distances, velocities (and therefore the engine volumetric efficiency) increase as the valves move away from the cylinder. The dependence is very strong for small distance values (lower than 2.5 mm) while it becomes weaker as the valve-wall clearance increases.