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The performance of multi-hole injectors designed for use in second-generation direct-injection gasoline engines has been characterised in a constant-volume chamber. Two types of multi-hole injector have been used: the first has 11 holes, with one hole on the axis of the injector and the rest around the axis at 30 degrees apart, and the second has 6 asymmetric holes located around the nozzle axis. Measurements of droplet axial and radial velocity components and their diameter were obtained using a 2-D phase Doppler anemometer (PDA) at injection pressures up to 120 bar, chamber pressures from atmospheric to 8 bar, and ambient temperatures. Complementary spray visualisation made use of a pulsed light and a CCD camera synchronised with the injection process.

Cavitation formation and development inside various types of nozzles for close-spacing spray-guided fuel injection systems is predicted using a computational fluid dynamics cavitation model. The fuel injection systems investigated include generic geometries of multi-hole nozzles and outwards opening pintle injectors. Model validation is performed against experimental data reported elsewhere in large-scale transparent nozzle replicas. The results confirm that cavitation strongly depends on the geometry of the nozzle and the operating conditions. For multi-hole nozzles, cavitation structures similar to those realised in Diesel injectors are formed. These include the needle seat cavitation realised at low needle lifts, the geometrically-induced hole entry cavitation and string cavitation developing inside the sac volume. A more chaotic and less understood cavitation pattern develops at the sealing area of inward seal band outwards opening nozzles.

A transparent enlarged model of a six-hole injector used in the development of emerging gasoline direct-injection engines was manufactured with full optical access. The working fluid was water circulating through the injector nozzle under steady-state flow conditions at different flow rates, pressures and needle positions. Simultaneous matching of the Reynolds and cavitation numbers has allowed direct comparison between the cavitation regimes present in real-size and enlarged nozzles. The experimental results from the model injector, as part of a research programme into second-generation direct-injection spark-ignition engines, are presented and discussed. The main objective of this investigation was to characterise the cavitation process in the sac volume and nozzle holes under different operating conditions. This has been achieved by visualizing the nozzle cavitation structures in two planes simultaneously using two synchronised high-speed cameras.