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Variable Valve Timing (VVT) technology is more and more adopted in modern spark-ignition engines for the optimization of torque delivery. Furthermore, a proper choice of valve timing could reduce the typical pumping losses of these engines thus improving fuel economy at part load. VVT mainly influences gas exchange processes, then the engine volumetric efficiency; in some circumstances, variations of valve timing could modify the charge composition and therefore the flame development and propagation. In this paper, the combustion process of a small displacement, 2 valve, spark-ignition engine, with variable valve timing, has been numerically and experimentally analyzed. The use of VVT allows obtaining combined internal EGR and Reverse Miller Cycle effects so to achieve a significant dethrottling at part load operation. A 3-D computer code has been utilized in order to calculate the details of the flow field within the cylinder and the combustion rate at different valve points.

Optimized valve timing, according to engine load, may lead to significant improvements in pumping losses and internal EGR generation. Thus, VVT technology constitutes an effective way to reduce both fuel consumption and pollutant emissions. In this paper, the behavior of a small displacement, 2 valve, Spark-ignition engine, with variable valve timing, has been numerically and experimentally analyzed. The use of VVT allows obtaining combined internal EGR and Reverse Miller Cycle effects so to achieve a significant dethrottling at part load operation. High EGR rates require high turbulence intensity in order to accelerate the combustion rate. The engine performs an accurate combustion chamber design and a tangential intake port able to generate optimized swirl motion, according to the engine speed and load, during both the exhaust gas re-aspiration and the intake stroke. Engine performances at different cam phaser positions have been calculated by means of a 3-D computer code.