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. Engine speeds of 2500, 3500 and 5000 rpm are analyzed for 10 degree crank angle and 30 degree crank angle of spark advance.
The results show the best position for the spark plug always bellow exhaust valve, but for 2500 rpm it is closer to the center of the combustion chamber, and for 5000 rpm it is closer to the wall among the three analyzed engine speeds. For all rotations, the 10° CA advance show results closer to the center of the combustion chamber, as for 30° CA spark advance it moves towards cylinder wall.