A simulation model of an injection system for reciprocating engines has been developed to study the influence of the geometrical and mechanical configuration of the injection apparatus on the injection flow characteristics. The suggested model simulates pressure wave propagation in the pipelines, particularly in presence of cavitation, and injector behaviour. The model used for nozzle simulation evaluates fluid-dynamic phenomena in the nozzle sections and chambers. This allows prediction of injector geometry influence on the flow parameters and simulation of general behaviour of the apparatus and the spray using different nozzles (with sac, without sac, with reduced sac). Lastly, a model of the structure by a finite elements method allows the study of dynamics of the moving elements. The mathematical model has been verified through a series of experimental measurements. The comparison between numerical and experimental results has been satisfactory.