The engine combustion, performance and emission characteristics are known to be influenced by the incylinder mixing induced due to several factor. In this work, the role of reciprocating piston on the incylinder flow in motoring conditions is investigated on an optical test rig designed for understanding the flow development during charge compression. The flow measurements are carried out using Particle Image Velocimetry (PIV) at varying engine speeds for different piston configurations. The results at those conditions are analyzed through Computational Fluid Dynamics (CFD) and Proper Orthogonal Decompositon (POD) tools. Typical results comparing PIV measurements with CFD and the flow turbulence using POD are discussed.

The agreement between the PIV measurement and the CFD simulation in a base line case of a flat piston configuration and 600 rpm speed condition is qualitatively reasonable. For this case, POD analysis on measured instantaneous velocity points to the transfer of energy from mean flow to turbulence particularly during the later part of compression. The CFD estimates concerning normalized turbulent kinetic energy obtained during parametric analysis for the three piston geometries viz. flat, cylindrical and spherical at crank speeds between 400-1200 rpm, reveal a linear scaling of these quantities with mean piston kinetic energy. The turbulent kinetic energy is higher in case of spherical cavity-in-piston than cylindrical and flat pistons.