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In-cylinder direct fuel injection technology is effective in improving fuel consumption and reducing emissions for gasoline engines. A number of systems based on this technology are currently being developed, and one such system, the wall guided DISI, has already been put to commercial use. As the development of the DISI engines pushes forward, spray guided DISI has been proposed as a new possibility which can offer further improvements. The authors of this paper recognize the advantages of spray guided DISI in terms of fuel consumption and emissions reduction, and have conducted research for the purpose of creating an injector that is optimized for spray guided combustion. A spray guided DISI engine requires a fuel injection system that is little affected by changes in airflow, pressure, and temperature inside the cylinder. This requirement is satisfied by the recently-developed multiple hole injector.

A Spray Guided DISI (Direct Injection Spark Ignition) is being proposed as a next-generation DISI and is expected to reduce the fuel consumption and the emissions than a Wall Guided DISI that is currently in the mainstream. With the aim of developing a Spray Guided DISI, the evaluation technologies for the spray behavior and the combustion characteristics in a single cylinder transparent engine, the measurement technologies for the mixture formation by LIEF (Laser Induced Exciplex Fluorescence) method and using a Fast Response FID (Flame Ionization Detector), and the analysis technologies for the spray behavior and the mixture formation with CFD (Computational Fluid Dynamics) technology were established. Based on these evaluation techniques, the behavior of spray and mixture formation by a Swirl Injector and a Multi Hole Injector were evaluated.

Spray guided DISI, a next-generation DISI system, is now under development as a gasoline engine which will contribute to improving fuel consumption. The authors have carried out a study to improve fuel consumption and exhaust emissions resulting from a spray guided DISI system with a center injection structure, which is being developed as a system with superior combustion stability. The primary issue for the center injection structure is to reduce changes in the fuel spray characteristics resulting from carbon deposits near the injector nozzle holes. The secondary issue for this structure is to improve the mixture formation.