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Injection rate control is an important capability of the ideal injection system of the future. However, in a conventional Common-Rail System (CRS) the injection pressure is constant throughout the injection period, resulting in a nearly rectangular injection rate shape and offering no control of the injection rate. Thus, in order to realize injection rate control with a CRS, a "Next- generation Common-Rail System (NCRS)" was conceptualized, designed, and fabricated. The NCRS has two common rails, for low- and high-pressure fuel, and switches the fuel pressure supplied to the injector from the low- to the high- pressure rail during the injection period, resulting in control over the injection rate shape. The effects of injection rate shape on exhaust emissions and fuel consumption were investigated by applying this NCRS to a single- cylinder research engine.

Injection rate shape control is one feature of a diesel fuel injection system that is strongly desired at this time. However, in the conventional Common Rail System (CRS), it is difficult to control the injection rate because the injection pressure is constant during the injection period, resulting in a nearly rectangular rate shape. Thus, in order to achieve injection rate control in a CRS, a Next-generation Common Rail System (NCRS) was designed and the prototype system was fabricated. With two common rails, one for low pressure fuel, and the other for high pressure fuel, the NCRS achieves injection rate shape control by controlling the fuel injector supply pressure, from the two rails. The NCRS can achieve a clear “boot” shaped injection rate, and injection rig tests confirmed that the shape could be flexibly controlled via several control parameters.

With the intention of improving engine performance and emissions, the authors examined the influence of the method of initial fuel injection quantity reduction and of the injector configuration of a common rail fuel injection system on engine performance and exhaust emissions. Results showed that decreasing the nozzle hole diameter was an effective way to reduce the initial injection quantity without increasing black smoke. Compared to a three-way type injector, it was found that a two-way type injector can greatly reduce the amount of fuel leakage from the electromagnetic injector control valve and fuel consumption could be further improved by reduction of the driving loss. Furthermore, the increase of driving losses with higher injection pressure was small, and as a result, higher pressure injection was possible.