Investigations of Spray-Induced Vortex Structures during Multiple Injections of a DISI Engine in Stratified Operation Using High-Speed-PIV

Modern gasoline direct injection engines with spray-guided combustion processes require a stable and reliable fuel mixture formation as well as an optimal stratification at time of ignition. Due to the limited time for this process the temporal and spatial analysis of the in-cylinder flow field and its influence is of significant interest. The application of a piezo injector with outward opening nozzle and its capability to realize multiple injections within the compression stroke provides additional degrees of freedom for the stratified engine operation. To improve the performance of this combination a detailed knowledge of the in-cylinder flow field and its interaction with the spray propagation during and after multiple injections is essential. The flow field measurements were applied in an optical borescope single-cylinder research engine using a high-speed particle image velocimetry (HSPIV) setup. Focusing on real engine operation all investigations were performed in fired condition. The endoscopic PIV setup was used to capture the instantaneous flow field at engines speeds of up to 3000 rpm. This goes along with a resolution of 0.5° crank angle degrees using a camera framing rate (cfr) of 36 kHz. For every operating point the interaction between the spray propagation and the tumble motion was visualized for 100 individual consecutive combustion cycles. The results demonstrate the capability to use a high-speed PIV setup to identify the interaction for mean-averaged data-sets as well as for individual combustion cycles. The vortex formation and movement is analyzed with the calculated velocity vectors, the averaged kinetic energy, and the turbulent kinetic energy.