Characteristics of the in-cylinder flow and spray for intake valve timing in an optical GDI engine with spray-guided injection

Abstract

In this study, the correlation between the spray and in-cylinder flow was investigated in a two-cylinder optical gasoline direct-injection engine with spray-guided injection under various injection timings and intake valve open timings. Particle image velocimetry measurements were performed to evaluate the in-cylinder flow characteristics quantitatively. The intake valve timing significantly affected the in-cylinder flow intensity and structure. Different in-cylinder flow intensities and structures caused different effects of the fuel injection on the in-cylinder flow. In the strong in-cylinder flow conditions, the fuel injection disturbed the flow development, such that the flow was weakened after fuel injection and a high spray cycle-to-cycle variation was shown. In all intake valve timing conditions, there was no significant effect of fuel injection on the increase in turbulent kinetic energy at the end of compression stroke under injection timing of BTDC 270 °. In the injection timing of BTDC 180 °, turbulent kinetic energy increased over 40 % after fuel injection compared to the conditions without fuel injection. This trend was seen across all intake valve timing conditions. Therefore, when the injection timing was delayed, the dominant factors determining the flow intensity and structure can be the spray pattern, injection pressure, and injection duration.