The introduction of the high-pressure fully electronic-controlled injection systems has opened a number of new possibilities to optimize diesel engine performance and to reduce pollutant emissions. However greater research efforts are required to meet future European emission legislation. The control of the combustion process, which determines to a large extent the amount of pollutant emissions, requires primarily an understanding of its physics and chemistry as well as the capability to modify one or more of the interdependent process parameters in a given direction. Since many parameters have to be considered, a combined experimental-numerical approach is required. In this context, the research group of the University of Rome "Tor Vergata", which has developed a multidimensional code for diesel engines simulation based on the KIVA 3V code, and the research group of the University of Perugia, which has built a laboratory for the characterization of diesel and SI injection systems and sprays, have been collaborating for many years. The implemented models in the multidimensional code enable full 3D computation of both gas and fuel spray dynamics to be made, including atomization, vaporization, autoignition and combustion. However, spray development, mixture preparation and combustion depend on the fuel injection system characteristics and actual operating conditions. Therefore, modelling of the fuel injection system is essential to correctly predict all those parameters involved in the fuel injection, which are still often considered as constant input data in 3D simulations. In this paper a 1D model, built in the AVL HYDSIM environment, of the CR injection system of the University of Perugia laboratory is presented and reliability of numerical results is tested through a comparison with experimental data. Then, 3D simulations of diesel spray development are performed coupling the 1D model of the injection system to the multi-dimensional code.