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Visualization plays an effective role in the establishment of a new combustion concept by helping to find the optimal results quickly among many different parameters and contributing to a shorter development period. Laser-induced fluorescence, Raman scattering and infrared absorption were used to measure the air/fuel ratio quantitatively in a third-generation direct-injection gasoline (DIG) engine with a spray-guided mixture formation process and comparisons were made with the mixture formation concepts of the first- and second-generation DIG engines. The optimum combination of fuel spray, gas flow and combustion chamber configuration was found to be different for the three generations of DIG engines. The characteristics of the stable combustion region for obtaining higher thermal efficiency and cleaner exhaust emissions differed among the three mixture formation concepts.

Vehicle manufacturers developed two mixture formation concepts for the first generation of gasoline direct-injection (GDI) engines. Both the wall-guided concept with reverse tumble air motion or swirl air motion and the air-guided concept with tumble air motion have the fuel injector located at the side of the combustion chamber between the two intake ports. This paper proposes a new GDI concept. It has the fuel injector located at almost the center of the combustion chamber and with the spark plug positioned nearby. An oval bowl is provided in the piston crown. The fuel spray is injected at high fuel pressures of up to 100 MPa. The spray creates strong air motion in the combustion chamber and reaches the piston bowl. The wall of the piston bowl changes the direction of the spray and air motion producing an upward flow. The spray and air flow rise and reach the spark plug. The fuel injection pressure, the spray shape and the piston bowl geometry are important factors for the performance of stratified combustion with this concept.