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Injection process simulation methods were developed for both the unit injector (UI) system and the pump-line nozzle (PLN) system consisting of an in-line injection pump, fuel line, and nozzle. Simulation results agreed well with measured ones. With regard to the shape of injection rate and the peak injection pressure change at various engine speeds, the injection characteristics of the UI system are better than those of the PLN system. Simulation results showed that similar injection characteristics can also be obtained with the PLN system by using a concave cam with a carefully designed cam profile for a sleeve-controlled in-line injection pump and by changing the prestroke according to the operating conditions. Engine test results demonstrated the possibility of improving the trade-off between NOx and fuel consumption by shaping the injection rate. The shape of injection rate plays an important role in diesel combustion(1,2)*, affecting exhaust emissions and also combustion noise.