A PART OF MARELLI
The increasingly stringent regulations on engine polluting emissions and on fuel consumption reduction, both in terms of carbon monoxides, nitrogen monoxides, unburned hydrocarbons and particulate matter, and in terms of emissions of greenhouse gases, drive the more and more advanced study of the coupling between the engine injection system and the engine itself.
In particular, recent regulations concerning gasoline engines with direct injection set strict limits on the emission of particulate matter, while the need for a reduction in fuel consumption leads to a considerable downsizing of the engine.
The shape of the spray that forms in the combustion chamber plays a crucial role in the search for improved performances. The definition of the spray in the engine is spray targeting, and its objective is to ensure the proper formation of a homogeneous or stratified blend, depending on the engine management methods, with a high rate of repeatability for the entire operating time of the engine, thus reducing and controlling the generation of fuel film on the walls of the combustion chamber and guaranteeing high jet atomization.
The shape of the spray is strongly affected by the operational conditions of the engine and by the different control parameters of the injection system, such as injection pressure, injection start and length, and quantity and distribution of the injections in the single engine cycle. The interaction between the spray and the air motions inside the cylinder and the droplet vaporization method (with the possibility of flash-boiling) represent determining factors in the definition of the spray target.
The injector is designed and built to determine the shape of the spray target, which must be designed together with the combustion chamber or adapted to it. During the initial phases of the design, the extensive use of CAE software for the computer-aided design allows, through simulations, to create and optimize the spray pattern for the engine being designed: in addition to speeding up the design process, the use of sophisticated simulation models makes it possible to analyze phenomena that would otherwise be difficult to observe. The virtual simulation of the entire engine, and specifically the three-dimensional simulation of the combustion chamber with the spray, is then accompanied by experimental validation. The developed spray targeting methodology allows the best solution to be found for all types of GDI engines (side-mounted o centred-mounted, aspirated or charged, etc.).