An experimental analysis of the turbulent structures generated by the intake port of a DISI-engine

摘要

An essential task in the optimization of combustion processes for DISI (Direct Injection Spark Ignition) engines is the generation of a suitable in-cylinder flow, leading to easy ignition conditions and low pollutant emissions. Therefore, the determination of the transient flow behaviour generated in the cylinder by the intake port and the identification of the origin of flow fluctuations are equally important. A better insight into the time-dependent behaviour of in-cylinder flow is necessary to avoid unwanted flow variations and enhance the fuel-mixture preparation. Suitable information is provided here by the experimental measurement of instantaneous flow fields in a model cylinder flow, as obtained from High Speed Particle Image Velocimetry. The investigated flow fields are generated by a four-valve DISI production engine cylinder head on a steady-state test-bed. The present paper presents a procedure based on Singular Value Decomposition (SVD) in order to filter out measurement errors and to obtain information about the transient behaviour of in-cylinder flows. First, the procedure is presented and analyzed by considering generic vector fields, demonstrating that information concerning the transient behaviour is detectable in this manner. Next, the transient behaviour of the in-cylinder flow is investigated by reconstructing flow fields with the SVD procedure. The reconstruction employs a specified number of SVD spatial modes φ _i (x) and corresponding SVD time coefficients a _Di (t), which are reduced to their deterministic parts. Afterwards, the reduced SVD time coefficients a _Di (t) are used to determine the main fluctuation frequencies of the in-cylinder flow and to identify the origin of these fluctuations.