Experimental study of high pressure sprays for SIDI engines

In the last years many different injection and combustion strategies have been proposed for Spark Ignition Direct Injection (SIDI) engines. Different type of injectors (swirled, shaped, air-assisted, multi-hole) have been used by manufactures with features related to the air/fuel mixture formation. Multi-hole injectors, working like diesel valve coverage orifice (VCO) or mini-sac nozzle, seem to be the future trend for GDI (Gasoline Direct Injection) applications. The multi-hole approach makes the fuel distribution in the combustion chamber very versatile, being possible to act on the holes number and their shape, spray footprint and hollow-cone structure, offset of fuel pattern respect to the injector axis and variable angle between the jets. An experimental study on SIDI engine sprays, generated by a diesel-like electronically controlled Common Rail injection apparatus, has been performed. Space- and time-resolved spray behaviour study from a single hole nozzle has been carried out in an optically accessible vessel. The injection pressure and the backpressure were explored up to 100 MPa and 1.2 MPa, respectively, at ambient temperature. A gasoline-like fluid (EXXSOL D40) was injected through a single hole nozzle (0.18 mm in diameter and 1.0 mm in length). Such a simple injector geometry has been chosen to acquire preliminary data, useful to calibrate provisional numerical codes and to determine suitable injection strategies. The emerging sprays have been lightened along their axis by a pulsed sheet generated on the second harmonic of a Nd-YAG laser at different times from the start of injection. The scattered light has been collected at 90° by a CCD camera with the frame grabber synchronized with the injection command and the laser pulse. An image processing software has been used for analysing the images and for extracting the global parameters of the jets.