A new stratified charge combustion system has been developed for direct injection gasoline engines. The special feature of this system is the use of a thin fan-shaped fuel spray formed by a slit nozzle. The stratified mixture is prepared by the combination of this fan-spray and a shell-shaped piston cavity. Both under-mixing the and over-mixing of the fuel in the stratified mixture is reduced by this system. This combustion system does not require a distinct charge motion such as tumble or swirl, which allows the intake port geometry to be simplified in order to improve the full-load performance. This paper first describes the theoretical background, which focuses on the mixing speed of the fuel with air in the cylinder during the compression stroke. Next, the major characteristics of the fan-shaped spray are shown and compared to the cone sprays with swirl nozzles. Finally, some spray effects on engine performance are described. The fuel consumption and emissions such as smoke, CO and HC are greatly improved at medium load and medium engine speed.
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