An Experimental Study of In-Cylinder Air Flow in a 3.5L Four-Valve SI Engine by High Speed Flow Visualization and Two-Component LDV Measurement

In-cylinder flows in four-valve SI engines were examined by high frame rate flow visualization and two-component LDV measurement. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence later in the cycle. The exact nature of this relationship is not well known. However, control of the turbulence offers control of the combustion process. To develop a better physical understanding of the in-cylinder flow, the effects of the cylinder head intake port configuration and the piston geometry were examined.

For the present study, a 3.5L, four-valve engine was modified to be mounted on an AVL single cylinder research engine type 520. A quartz cylinder was fabricated for optical access to the in-cylinder flow. Piston rings were replaced by Rulon-LD rings. A Rulon-LD ring is advantageous for the optical access as it requires no lubrication.

Four different cylinder head intake port configurations and two piston geometries were studied using a high speed flow visualization technique. Examination of these films suggested that quantitative velocity measurements be conducted for the two different piston configurations. The effect of the piston geometry on the in-cylinder flow was examined by LDV measurement. The flow visualization shows that cylinder head intake port configuration plays a significant role in the generation of initial tumble motion in the early stage of the intake stroke. While the in-cylinder flow is developing, the pop-up piston geometry accelerates the flow field in the axial direction, which provides the strong tumble motion. This may result in an improvement in small-scale turbulence late in the compression stroke.