The reduction of exhaust gas emissions is an urgent and an important task for diesel engines. A 4-valve per cylinder arrangement represents one of the technological advances towards this objective. This paper explains experimentally the formation process of in-cylinder air motion for both 2 and 4 valve heads using steady state air flow apparatus. Experimental methods used for the visualization and the velocity measurements were a tracer laser sheet technique (TLS) and laser doppler velocimetry (LDV), respectively. The experimental results are summarized as follows. In-cylinder air motion of 2 and 4 valve heads were visualized and measured by TLS and LDV. The two valve cylinder head mainly generates the swirl cylinder head mainly generates the swirl motion by a strong vortex from the helical port. The swirling flow expands outward from the cylinder center to the cylinder periphery as it goes down through the cylinder. On the contrary the 4 valve cylinder head mainly generates the swirl motion by strong flow around the cylinder periphery from the directional and the helical ports. As the flows progress, the outer flow effects on the inner flow. When the flow patterns vary greatly such as between a 2 valve head and a 4 valve head, the impulse swirl meter is preferable to the vane type meter in order to measure bulk swirl strength. (A)
Abstract