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It is well known that indirect injection (IDI) diesel engines have better exhaust performance but lower fuel economy than direct-injection (DI) diesel engines. In recent years, fuel efficiency has been strongly demanded to reduce global warming. Therefore, the IDI engine is required to reduce fuel consumption. According to past research, fuel injection control can be one of the means to improve fuel efficiency in the IDI system. This paper tried to apply two-stage fuel injection as one of the fuel injection control methods to improve fuel efficiency while suppressing exhaust emissions. Particularly, since it is considered necessary to reduce the amount of injection during the ignition delay period in the sub-chamber with the IDI type, two-stage injection with a small amount of pilot injection was applied.

In this study it is tried to reduce NOx and particulate emissions simultaneously in a direct injection diesel engine based on the concept of two-stage combustion. At initial combustion stage, NOx emission is reduced with fuel rich combustion. At diffusion combustion stage, particulate emission is reduced with high turbulence combustion. The high squish combustion chamber with reduced throat diameter is used to realize two-stage combustion. This combustion chamber is designed to produce strong squish that causes high turbulence. When throat diameter of the high squish combustion chamber is reduced to some extent, simultaneous reduction of NOx and particulate emissions is achieved with less deterioration of fuel consumption at retarded injection timing. Further reduction of NOx emission is realized by reducing the cavity volume of the high squish combustion chamber. Analysis by endoscopic high speed photography and CFD calculation describes the experimental results.