Experimental and numerical study of an air assisted fuel injector for a D.I.S.I. engine

The transient behaviour of the fuel spray from an air assisted fuel injector has been investigated bothnumerically and experimentally in a Constant VolumeChamber (CVC) and an optical engine. This two phaseinjector is difficult to analyse numerically andexperimentally because of the strong coupling betweenthe gas and liquid phases. The gas driven atomization ofliquid fuel involves liquid film formation, separation andbreak up and also liquid droplet coalescence, break up,splashing, bouncing, evaporation and collision. Furthermore, the liquid phase is the dominant phase inmany regions within the injector.Experimental results are obtained by using Mie scattering, Laser Induced Fluorescence (LIF) and Laser Sheet Drop sizing (LSD) techniques. Computational results are obtained by using a mixed Lagrangian/Eulerian approach in a commercial Computational Fluid Dynamic (CFD) code. Injector rig results show a good atomization of the spray with lowspray width and penetration and Sauter Mean Diameters SMD) of droplets of order 10 ?m. Engine results show a spray with a relatively low penetration producing liquid fuel and vapour fuel concentrations close to the central location of the injector and spark plug for stratified, lean mode of operation. Imaging of this injector operating inside an engine confirms the overall design approach for stratified operation.