The behaviourt of small- and large-scale variations of in-cylinder flow during intake and compression strokes in a motored four-valve spark ignition engine

Abstract

An experimental study was conducted to investigate the small-scale and large-scale variations of flow within the cylinder of an internal combustion engine (turbulence and cyclic variation) during the intake and compression processes. Spatial fast Fourier transform (FFT) filtering techniques with various cut-off lengths were used to determine whether there existed a particular length scale that differentiated turbulence from cyclic variations. The flow field was measured using a particle image velocimetry (PIV) system, which was set with 1.25 mm grid spacing. From the experiments and analysis, it was found that there was no particular size of vortical structures dominating the flow field during intake and compression strokes over many cycles. It was also found that not only the ensemble-averaged variation but also the standard deviation of the large- and small-scale variations were greater during the early intake and late compression compared with late intake through the early compression process.