Characterization of an evaporating direct-injected gasoline spray using laser-induced exciplex fluorescence and particle image velocimetry techniques

Abstract

The purpose of this study is to characterize an evaporating direct-injected (DI) gasoline spray from a high-pressure swirl injector using the laser-induced exciplex fluorescence (LIEF) technique and particle image velocimetry (PIV). A fluorobenzene/diethylmethylamine (DEMA) system was used as the exciplex-forming dopants. The behaviour of the liquid and vapour phases was analysed by image processing. For the analysis of vorticity inside the spray, droplet velocity data obtained by PIV were used. The experiments were performed at two ambient temperatures (293 and 473 K) and three different ambient pressures (0.1, 0.5 and 1.0 MPa). It was found that ambient temperature had a significant effect on the axial and radial growth of the liquid phase of the evaporating spray at atmospheric pressure while it had little effect under elevated pressures. Radial growth of the vapour phase of the evaporating spray was more dominant than axial growth under high temperature and pressure conditions. As the ambient pressure was elevated, the liquid phase of the spray transformed from a hollow cone to a solid cone of bell shape, while the vapour phase varied from a widespread distribution to a compact shape with a locally richer mixture. The evaporating spray could be divided into two spray regions from the analysis of vorticity and the distributions of liquid and vapour phases. The cone region (penetrations of 0.3-0.5) was mainly liquid phase and disappeared rapidly at the end of injection. The mixing region contained the active interaction between entrained air and fuel vapour.