The article presents results of the 3D-CFD modeling of mixture creation process in the cylinder of diesel engine. The simulation was performed using the AVL Fire software. Based on the geometry of the ADCR engine, produced by Andoria-Mot Company, a 3D-CFD model of combustion chamber, channels in the engine head and CNG injector nozzle were created. This model prevented the simulation of the filling, compression and mixture creation process. Specially prepared CNG injector has been placed in the socket of the glow plug, to minimize interference with the structure of the engine. With this solution full functionality of the original fuel supply system was retained with the ability to work with one or two fuels. During studies the location of the gas injector nozzle was changed. The results of simulation are presented for three variants of CNG injector locations. Simulation studies prevented the determination of the degree of stratification and the distribution of fuel in the cylinder of the engine. Influence of the injector nozzle position on the air-fuel stratification in the cylinder was demonstrated. The characteristics of the fuel mass in piston bowl and the rest part of the cylinder were also analyzed. As a result of the simulation, the optimal position of the injector nozzle was presented.