Charcterization of the mixture formation process in a GDI engine operating under stratified mode

The paper is intended at an experimental and a numerical study of the mixture formation process in a GDI engine equipped with a high-pressure seven-hole injector. One of the 4 engine cylinders is modified to allow two optical accesses that leave unvaried the combustion chamber configuration, hence the performance and emis-sions of the real engine. A first optical access is through the piston head and a second one is through an endo-scopic fiber probe inserted in the cylinder head. Under a medium-speed, medium-load working condition, the gasoline injection phase is experimentally characterized by image acquisition with high temporal resolution.The considered injector is also preliminary experimentally characterized as delivering gasoline into an opti-cally accessible confined vessel under various injection strategies. Spray images are collected to derive infor-mation relevant to penetration length and cone angle. The issuing mass flow rate is measured by means of a Bosch tube. The measurements data base is used to develop a 3D numerical model of the spray dynamics, whose validation is performed through an automatic procedure. The spray model is included within a 3D model of the in-cylinder processes to realize a reliable description of mixture formation and combustion.