Abstract
Abstract The transient dynamics of air flow running through the moving intake valve gaps in combustion cylinders is crucial to the performance of spark-ignition direct-injection engines. However, research on the air flow behavior in the vicinity of valve exits is still limited. In this work, transient air flow characteristics of a custom-designed dual-valve system under the operating conditions of a fixed valve lift and a vibrating valve lift at two frequencies are experimentally investigated. The velocity vector field measured using planar particle image velocimetry (PIV) is first analyzed in time domain based on temporal mean and root-mean-square (RMS) values. Comparison of temporal mean flow fields reveals the difference in flow pattern while RMS represents the variation of intake air jet velocity along the inlet path of the vibration-affected jet. Instantaneous snapshots provide direct analysis of the valve vibration-induced intake air jet behavior. Furthermore, investigation in frequency domain extends insights into the dominant spectral components of flow structures. Fast Fourier transform (FFT) applied to every vector on the velocity field yields a vibration frequency affected zone (VFAZ), indicating the regions where the effect of valve vibration is significant. By employing dynamic mode decomposition (DMD) method, the spatio-temporal PIV results are decomposed into modes with specific frequencies. Reconstructed flow field using modes with the valve operating frequency visually unveils a cyclic vortex structure near the valve exit. In summary, this study elucidates the mechanism of near-valve intake air flow impingement and interaction behavior induced by the valve vibrating motion.
Published Version
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