Transient 3D analysis of a DI gasoline injector spray

A cycle-resolved, phase Doppler anemometry (PDA) methodology is appraised for the collection and analysis of data from a gasoline fuel injector. A high-pressure swirl injector is utilized, spraying unleaded gasoline into air at ambient pressure and temperature. Results are presented in terms of Sauter mean diameter (SMD) of droplets, three components of velocity, and semiquantitative mass flow rate for the entire flow field. Spray development is analyzed using time increments of between 0.25 ms and 1 ms over the first 12 ms after injection. High-speed photography confirms the validity of some of the global trends identified, including head vortex development, spray penetration, and needle bounce. PDA measurements indicate that larger droplets are produced in the early stages of the injection. These populate the head and periphery of the spray cone, which becomes essentially hollow for a period between 0.75 and 2 ms. Smaller droplets in the center of the cone attain velocities in excess of 50 m/s, while those on the edge are entrained by the recirculating head vortex. During the early injection period, the majority of the liquid mass resides within the "head" and an annular section of the spray, which indicates the hollow cone design. After 3 ms, the spray becomes more homogenous, with little mass flow rate variation across the cone identifiable after 4.5 ms. The data are finally compared with a standard time-averaged correlation usually utilized for this type of injector. This emphasizes the need for continued effort on transient predictive spray modeling in future direct-injection (DI) gasoline investigations