Flexibly Controlled Injection Rate Shape with Next Generation Common Rail System for Heavy Duty DI Diesel Engines

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. For example, the rate and duration of the low-pressure initial stage boot portion can be obtained from the low-pressure rail pressure and switching valve opening time. On the other hand, the main (high-pressure) injection rate is controlled by the high-pressure rail pressure, with a duration controlled by the injector solenoid valve. In addition, the NCRS system was installed on a single cylinder diesel research engine, and testing was carried out. These tests showed that NCRS with injection rate shape control could significantly improve the NOx-fuel consumption and NOx-PM trade-offs.