High-speed tomographic PIV measurements in a DISI engine

Abstract

Engine processes require fundamental knowledge on specific fuel–air mixtures to reduce pollutant emissions, i.e., soot formation, $\hbox {CO}_2$, and $\hbox {NO}_{x}$ generation, and to improve engine efficiency. However, the in-cylinder flow field of combustion engines is characterized by time-dependent and highly three-dimensional large-scale flow structures and cycle-to-cycle variations (CCV). This means that high-speed volumetric velocity measurements are required to investigate three-dimensional large-scale flow structures and CCV inside the combustion chamber at high temporal resolution. Since such data are hardly available in the literature, a high-speed tomographic particle image velocimetry (HS-TPIV) setup is used to measure the velocity field in an internal combustion engine at an engine speed of 1500 rpm and at a temporal resolution of $10\,^\circ$ crank angle in a maximum measurement volume of $50\times 8\times 83\,\hbox {mm}^3$. To assess the quality and the validity of the high-speed volumetric measurements, the HS-TPIV results are validated using high-speed stereoscopic particle image velocimetry measurements in the engines tumble plane. To further verify the measurement quality, an extensive error estimate is conducted. Finally, the instantaneous, three-dimensional measurement results are used to analyze the impact of fluctuations due to turbulence and CCV on the flow field in several instantaneous engine cycles at several predefined crank angles. The investigation shows the three-dimensional extent of flow fluctuations inside combustion engines and qualitatively quantifies the effect of CCV in in-cylinder flow.

Graphic abstract