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In the diesel engine field, increasingly strict emission regulations and customer requirements have necessitated advanced technology. One important subject for diesel engines is cold startability and white smoke under cold conditions. In this paper, the combustion mechanism of a multi cylinder engine under cold conditions is discussed. First, during a starting condition, it is proved that the cold flame, which is caused by previously misfired fuel during intermittent combustion, promotes good combustion on the following cycle. Secondly, following engine starting, it is estimated that there is minimum fuel quantity above which combustion is carried out. The minimum fuel quantity depends upon the temperature of the combustion chamber. Unbalance between the minimum fuel quantity and actual injection quantity results in white smoke emission.

To meet the 1990s' requirements for diesel engines, the realization of innovative fuel injection system has been expected. Thus the fuel injection system named ECD-U2 was newly developed. ECD-U2 is the electronic unit injector system with high pressure common rail of which features are explained as follows; Fully electronic and flexible control in fuel quantity and injection timing. Adjustable injection rate shape Optimum injection pressure control Superior packageability and low drive torque loss. In this paper, design strategies, actual hardware configurations and some test results of ECD-U2 are described.