The paper presents a comparative analysis of the parameters of the injection process in unit injector and pump line nozzle systems. The analysis is based on numerical programs which simulate the working processes of the both systems. The basic assumptions underlying the physical models used in these programs are discussed and the good agreement between numerical results and actual processes is shown. The analysis takes into account the most important parameters for the combustion performance efficiency of injection and durability of the system. The results confirm the essential advantages of unit injection systems for fuelling high-speed diesel engines with direct injection.