Tomographic Particle-Image Velocimetry Analysis of In-Cylinder Flows

New combustion processes require an understanding of the highly three-dimensional flow field to effectively decrease fuel consumption and pollutant emission. Due to the complex spatial character of the flow the knowledge of the development of the flow in an extended volume is necessary. Previous investigations were able to visualize the discrete three-dimensional flow field through multi-plane stereoscopic PIV. In this study, cycle resolved tomographic particle-image velocimetry measurement have been performed to obtain a fully resolved representation of the three-dimensional flow structures at each instant. The analysis is based on the measurements at 80 degrees, 160 degrees, and 240 degrees after top dead center(atdc) such that the velocity distributions at the intake, the end of the intake, and the compression stroke at an engine speed of 1,500 rpm are discussed in detail. The flow fields are analyzed by distributions of the velocity fields, the turbulent kinetic energy (TKE), and the Gamma(1) vortex identification function. It is the purpose of these tomographic measurements, which enable the instantaneous resolution of the large scale three-dimensional vortical structures of the in-cylinder flow field during the intake and compression stroke without any discrete multi-plane composition of the spatial flow structure, to confirm the development of the ring vortex, the U-shaped structure of the tumble vortex, and the elliptic trajectory of the inlet vortex core. The three-dimensional resolution of the flow field will be used to show the growth of the turbulent kinetic energy due to the free-shear layers in the valve region and its volumetric distribution caused by the tumble vortex which gives insight into the mixing process during intake and early compression.