ISBN 9783843913225

978-3-8439-1322-5, Reihe Strömungsmechanik

Isabella Maria Bücker
Experimental Investigation of the In-Cylinder Flow of an Internal Combustion Engine

132 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2013), Softcover, A5

Zusammenfassung / Abstract

The in-cylinder flow structures that evolve during the intake and compression strokes of an internal combustion engine are of crucial importance for the mixing and the combustion process, and thus for its efficiency. In this work the non-reacting flow field within the combustion chamber of a motored direct-injection spark-ignition (DISI) engine with tumble intake port is measured. First, a two-velocity component particle-image velocimetry (PIV) system is set up and applied to the flow field in eight axial planes. The results are compared to the results of an engine with low tumble intake port. The superiority of the high tumble intake port for DISI application is pointed out. Furthermore, these measurements demonstrate the three-dimensionality of the flow, which necessitates the measurement of all three velocity components via stereoscopic PIV (SPIV) in multiple planes. Since the SPIV in angular camera setup is applied for the first time to engine in-cylinder flow, the 2C PIV measurements also serve as a reference test case. The arising problems and solutions are discussed in detail. The SPIV is then applied at 15 crank angles during the intake and compression strokes, showing the temporal evolution of the flow field. The flow fields are obtained within a set of 14 axial planes, covering nearly the complete cylinder volume. From these planes, the three-dimensional flow field is reconstructed and analyzed using a new 3D vortex criterion. It is shown that the tumble vortex, which is the dominant flow structure, varies significantly regarding shape, strength, and position throughout the two strokes. The center of the tumble vortex moves clockwise through the combustion chamber. At first, the tumble has a c-shape which turns into an almost straight tube at the end of the compression. The kinetic energy of the flow is conserved by the conservation of the angular momentum of the rotating tumble until late compression. This conservation ensures through the excited air motion an enhancement of the initial air-fuel mixture. Small-scale structures are analyzed by the distribution of the turbulent kinetic energy, which is mainly produced by the turbulent intake air jet and, at a smaller scale, by the disruption of the tumble vortex at the end of the compression. Finally, the flow field is influenced by a variation of the intake valve timing. It is shown how this affects the tumble evolution and thus the energy contained in the flow.