Effect of the Swirl Control Valve on the In-Cylinder Air Motion in a Four-Valve SI Engine

The effect of the Swirl Control Valve (SCV) on the in-cylinder flow characteristics was studied using LDA measurement in a single cylinder four-valve spark ignition engine with a SCV. Mean velocity, root-mean-square (rms) velocity fluctuation, and frequency structure of the velocity fluctuation were analyzed to illustrate flow features under the SCV open and closed conditions. The results show that when the SCV is open, large-scale flow structure in the cylinder is mainly tumble vortex, which will distort and break up during the late stage of the compression stroke. The rms velocity fluctuation increases during the compression process and reaches its maximum at certain crank angle before TDC. Larger scale eddies and lower frequency structures in the flow field become more near the end of compression process due to breakup of the tumble. The rms velocity fluctuation in the combustion chamber is roughly uniform at the end of the compression process. When the SCV is closed, however, strong swirl motion produced in the intake process sustains up to the end of compression process. The mean velocity in the cylinder is nearly doubled and the rms velocity fluctuation in the central area of the combustion chamber increases by about 30% compared with the SCV open condition. Smaller scale eddies and higher frequency structures in the flow field increase considerably. And the rms velocity fluctuation in the combustion chamber becomes non-uniform due to its higher value in the central area of the combustion chamber and lower values near the chamber wall.