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. The results showed that it was possible to control combustion by controlling the injection rate using the NCRS, and to improve the NOx fuel consumption and NOx-PM trade-offs, resulting in significant emissions reduction and improved fuel consumption. For example, compared to the conventional CRS, constant fuel consumption NOx was reduced by 22%, and constant NOx fuel consumption was reduced by 2.6% both at lower PM levels. In this way, the NCRS has shown a strong potential to improve exhaust emissions and fuel consumption of diesel engines, making it a promising injection system for the future.