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Variable Valve Actuation system (VVA) is a technology developed for improving fuel economy, reducing emissions, and enhancing engine performance mainly by reducing pumping losses. Many automakers have used VVA in their engine projects with excellent results. Usually, VVA systems are built to control the valve events in four different ways: changing the amplitude of the valve lift, the valve opening angle, the valve closing angle or a combination of those modes. A special attention at the calibration activity is needed to reach the optimum performance of this system, beyond this, it was necessary to develop a different way to calibrate, much more focused on the development of the combustion and the gas exchange process requiring an intense use of a pressure indicating system. This work presents a comparison between different way of actuation in combustion analysis of a VVA system on a spark ignition engine.

The internal combustion engine flow field has direct influence on the engine performance regarding both power and emissions. The intensity, location and direction of the flow structures known as tumble, cross tumble and swirl are key parameters on design and development of combustion chamber, especially on the spark plug position. This paper presents a Computational Fluid Dynamics (CFD) analysis on the flow field structures inside a two valve engine through the late compression stroke using commercial three dimensional software. The magnitude of the velocity vector has been plotted as a scalar in a contour map, so the center of the vortex is represented by the zero velocity region. Special attention is given to the spark timing, for it's the most important instant for determining the center of the swirl vortex. This is because the zero velocity region is considered the best place for the spark plug position, from the fluid dynamic point of view.