Characteristics of induction flow in SI direct injection engine with dual variable Swirl Control Valve

The flame development and propagation in a SI engine is highly influenced by the level and structure of the flow turbulence near the spark plug. These turbulent characteristics near the time of combustion are the result of the induction and compression processes. The main source of turbulent kinetic energy in the engine is the induction process. This study investigates the swirl characteristics of the induction process using a Particle Image Velocimetry (PIV) system and an experimental rig of an actual cylinder head and a transparent acrylic cylinder liner. Three induction cases with different swirl valve settings were selected. The intake valve lift was adjusted in steps of 1 mm to a maximum opening of 7 mm. PIV images were collected at each swirl adjustment and each valve lift to acquire average velocity vector fields. The total velocity field was decomposed into large-scale and small-scale components using the LES homogeneous decomposition technique. The result shows that coherent and organized swirling cores were formed when the Swirl Control Valve (SCV) was partially closed. The vortex core at 50° SCV setting was compact and strong compared to the higher degree adjustment (90°). There was no clear organized swirling flow structure in the swirl plane in the case of full-open SCV induction, but a number of clockwise and counter clockwise vortices were observed. However, for this case, the small-scale vortex field analysis showed that breaking-up of the macrostructure occurred at a higher rate than in the partially-open cases.