An experimental study of the spray from an air-assisted direct fuel injector

The transient behaviour of the fuel spray from an air-assisted direct-injection spark ignition (DISI) fuel injector has been investigated experimentally in a constant-volume chamber. As the chamber and injection pressures were varied, ensemble-averaged planar images of the laser-induced fluorescence (LIF) and Mie scattering from the spray were obtained to measure the Sauter mean diameter (SMD) using the laser sheet drop-sizing (LSD) technique. The root mean square (r.m.s.) SMD was also calculated by combination of the r.m.s. LIF and r.m.s. Mie scattering signals. The effect of the injection and chamber pressures and the ambient air density on the SMD, spray tip penetration, and dispersion of the air-assisted fuel injector are determined. In keeping with recent numerical studies by the group, vortex structures appear to be shed from the injector tip in back-illuminated images, indicating that the air and liquid motion are strongly coupled. These results also show that the spray penetration and SMD vary significantly with injection and chamber density, and scalings of the spray's overall SMD and penetration are proposed that achieve reasonable clustering in the experimental results.