Investigation of the In-Cylinder Tumble Motion In a Multi-Valve Engine: Effect of the Piston Shape 971643
An experimental investigation is carried out on in-cylinder motion, during the intake and compression strokes of a spark-ignited multi-valve engine. This study is conducted on a single cylinder four valve research engine. The engine is equipped with several optical accesses on cylinder liner and cylinder head. The turbulence and local velocity in combustion chamber were measured by Laser Doppler Velocimetry. Furthermore, effects of different bowl shapes on turbulence, cycle by cycle flow variations, and tumble distortion were studied.
Tumble velocity field exhibits a triplet vortices structure composed of one vertical and two horizontal vortices. This structure is induced during the inlet stroke, and remains during compression. In the latest stage of compression, tumble is converted into a pair of horizontal vortices. Velocity measurements in the cylinder show a precession motion of tumble center. Distortion of tumble is very unstable and perturbed with a flat top piston. Cycle by cycle variations of tumble timing distortion is observed, increasing velocity fluctuations. A new approach to remove cycle by cycle variations at the end of the compression stroke, when computing cycle-resolved turbulence, is proposed.
Bowls reduce cycle by cycle flow variations and turbulence intensity at ignition. Furthermore, steady flow rig measurements, as LDV investigations on the single cylinder during the intake stroke, demonstrate the influences of the bowl location on the tumble charge angular momentum at the end of the intake stroke.