Two-phase PIV: Fuel-spray interaction with surrounding air

Abstract

The demand for improvement of combustion-engine processes leads to a great need for detailed experimental information about the complicated processes of injection, breakup and propagation of the fuel jet and the vaporization of the fuel. Thus, in the presented work it was the aim to visualize the air flow that is induced by the injected fuel jet and also to explore the air entrainment into the fuel spray. This was done using two-phase PIV (particle image velocimetry). The fuel jet was illuminated with a Nd:YAG PIV-laser and PIV analysis was done by simply measuring the elastically scattered light of the fuel droplets. For the investigation of the surrounding air propylene-carbonate doped with DCM-dye was dispersed and the droplets were added to the continuous gas flow upstream of the chamber. Scattered and fluorescence signals, respectively, were detected perpendicular to the laser sheet with a CCD camera. To detect the gas flow, the scattered light from the liquid fuel was suppressed by an OG 590 longpass filter glass that transmits the fluorescence signal of the DCM-dye. It was possible to measure both the fuel jet and the gas flow in the presence of the fuel spray and a clear separation of the two phases could be achieved. In both (fuel and air) vector pictures corresponding vortices could be identified near the air/fuel boundary layer. Maximum velocities in the jet are depending on the operation conditions up to 150ms-1 and the gas flow has typically a velocity of 1 to 10ms-1. In the region next to the injector the air was pressed away during the injection. After the end of the injection a strong fast air entrainment flow into this region can be observed that compensates the pressure difference. © 2008 Springer-Verlag Berlin/Heidelberg.