Direct Injection of High Pressure Gas: Scaling Properties of Pulsed Turbulent Jets

Existing gasoline DI injection equipment has been modified to generate single hole pulsed gas jets. Injection experiments have been performed at combinations of 3 different pressure ratios (2 of which supercritical) respectively 3 different hole geometries (i.e. length to diameter ratios). Injection was into a pressure chamber with optical access. Injection pressures and injector hole geometry were selected to be representative of current and near-future DI natural gas engines. Each injector hole design has been characterized by measuring its discharge coefficient for different Re-levels. Transient jets produced by these injectors have been visualized using planar laser sheet Mie scattering (PLMS). For this the injected gas was seeded with small oil droplets. The corresponding flow field was measured using particle image velocimetry (PIV) laser diagnostics. From the corresponding measurements, both the jet spreading angle and penetration have been determined according to different definitions and the inter-relation between these definitions has been examined. Results show that -beyond the initial transition period and almost up to the tip vortex region - (average) jet angle is almost constant. Furthermore, jet penetration is well predicted by correlations that implicitly assume momentum conservation at constant static pressure. Measurements suggest a different time-averaged velocity profile from that typically assumed in some of these correlations. Tip vortex position and size scale with transient jet penetration.