Comparison of PIV Measured Flow Structures in Two Four-Valve Piston Engines

The in-cylinder flow fields of two four-valve piston engines, one with tumble intake port (engine A) and one with filling port (engine B) are compared. The flow fields are measured using cycle resolved 2C/2D particle-image velocimetry (PIV) in 8 axial planes at chosen crank angles during the intake and compression strokes. Highly three-dimensional flow structures throughout the combustion chamber are shown. Engine A exhibits a strong tumble vortex with the highest flow velocities occurring in this vortex. The in-cylinder flow of engine B has its highest flow velocities directly beneath the intake valves during the intake stroke, exhibiting the high mass flow over the whole circumference of the inlet valves. This difference in the intake jet geometry is imposed by the different intake port geometries. The difference in the initial flow structure strongly influences the evolution of the flow field during later crank angles. The strong tumble vortex of engine A is conserved during the compression stroke, thus conserving the kinetic energy of the flow for the combustion. Such a flow pattern is desirable for air-guided, direct injection engines.