Experimental analysis of the two-phase flow field in internal combustion engines

Abstract The reduction of green house gases and other pollutant emissions is of highest interest in modern engine development. This can be achieved by increasing the engine efficiency. For this, new combustion processes are needed. Another possibility to decrease green house gas emissions is the combustion of bio-fuels. However, these new methods as well as the efficient combustion of bio-fuels require an understanding of the highly three-dimensional flow field inside the combustion chamber. In this study the non reacting flow in two different research engines is measured. The measurements in the first research engine focus on the understanding of the highly three-dimensional structure of the flow field inside the combustion chamber. For this, holographic and tomographic particle-image velocimetry (PIV) have been applied to gain information on the intake and compression stroke of the research engine. The holographic PIV measurements show the feasibility of the technique to measure the highly unstable volumetric flow field. The analysis of the tomographic PIV measurements is based on the analysis of the flow field at 80◦, 160◦ , and 240◦ 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. Furthermore, the influence of an internal exhaust gas recirculation is analyzed at a crank angle of 240◦ atdc. The flow fields are analyzed by distributions of the velocity fields, the turbulent kinetic energy, and the 1 vortex identification function. The tomographic measurements enable the instantaneous resolution of the large scale three-dimensional vortical structures of the in-cylinder flow. Through this, the U-shaped structure of the tumble vortex core and the development of an elliptic ring vortex below the pent roof could be confirmed. Furthermore, the spatial distribution of the turbulent kinetic energy with high values below the intake valves could be shown. The analysis of the exhaust gas recirculation shows the tumble vortex to decompose at earlier crank angles. Furthermore, compared to the standard configuration, a higher turbulent kinetic energy could be shown.