Transient behaviour of the fuel spray from an air-assisted, direct fuel injector

The transient behaviour of the fuel spray from an air-assisted fuel injector in a constant volume chamber has been investigated experimentally. The relative Sauter mean diameter (SMD) of the spray droplets was determined using planar laser induced fluorescence (PLIF) and planar Mie scattering. Planar images of the ensemble averaged relative SMD with various injection conditions were obtained by calculating the ratio between the two laser light intensities at a given point. The penetration length and the spray shape factor were also obtained. The ensemble averaged results suggest the existence of vortices that are shed from the injector tip, and which entrain the smaller droplets. Results also show that the characteristics of the injector vary weakly with several particular injection parameters, notably the fuel injection pressure and the delay between fuel and air injection.