Topological flow evolutions in cylinder of a motored engine during intake and compression strokes

摘要

The evolution processes of the in-cylinder flows in the axial and diametral planes of a motored two-valve, single-cylinder, four-stroke engine during the intake and compression strokes are diagnosed by using a particle image velocimeter. A device, which is called the "inlet deflection-valve", being capable of deflecting the inlet flow is installed upstream of the inlet port. The engine cylinder, piston, and accessories are modified to meet the requirements of laser-light sheet shooting and camera viewing when the particle image velocimetry is applied. A conditional sampling technique is employed to acquire the instantaneous velocity data at predetermined crank angles. Ensemble averages of large amounts of the instantaneous velocity maps obtained at various crank angles present clear pictures of the evolution processes of the tumble and swirl motions in the engine cylinder. Sectional streamlines and the velocity vectors show the topological flow structures. The inception, establishment., evolution, and destruction processes of the swirling and tumbling vortical structures during the intake and compression strokes are presented and discussed, Quantified strengths of the rotating motions in the axial and diametral planes are presented by dimensionless tumble-and-swirl ratios, which are defined as the ratio of the mean angular velocity of the vortices in the target plane at a certain crank angle divided by the average crank angle velocity. By using the quantified nondimensional parameters, the correlation between the in-cylinder flow motions and the engine performance is analyzed and discussed.