The present study deals with the simulation of a Diesel engine fuelled by natural gas/diesel in dual fuel mode to optimize the engine behaviour in terms of performance and emissions. In dual fuel mode, the natural gas is introduced into the engine’s intake system. Near the end of the compression stroke, diesel fuel is injected and ignites, causing the natural gas to burn. The engine itself is virtually unaltered, but for the addition of a gas injection system. The CO2 emissions are considerably reduced because of the lower carbon content of the fuel. Furthermore, potential advantages of dual-fuel engines include diesel-like efficiency and brake mean effective pressure with much lower emissions of oxides of nitrogen and particulate matter. In previous papers [1, 2, 3], the authors have presented some CFD results obtained by the KIVA 3V and Fluent codes by varying the diesel/NG ratio and the diesel pilot injection timing at different loads. The calculations have been referred to a light duty direct injection diesel engine equipped at steady state test bench of Istituto Motori, where the experimental activity has been focused on the study of the combustion development, both in full diesel and Dual Fuel mode. Through a comparison between experimental and numerical results, a quite good fitting of the models has been realized. The phenomena involved in the cylinder are very complex and the numerical results obtained demonstrate a strong dependence on the boundary conditions imposed at the cylinder control system, provided by experimental data.Therefore, a comprehensive simulation of all engine should be necessary, by testing numerous operating conditions. In fact, the reduced experimental test cases available do not allow an overall view of the engine behaviour in the different operating conditions and cannot provide appreciable inlet conditions in cylinder for 3D combustion calculations. At the same time, the 3D results can definesome input(turbulence, combustion law, ..) for the one-dimensional simulation of the entire system fora preliminary calibration of some engine parameters. In particular, the calculations have been made by using an advanced 1D engine cycle simulation software enable to carry out performance simulations based on virtually any intake, combustion, exhaust system and turbocharger design, at different operating conditions, by varying alarge number of parameters.The program is based on one-dimensional flow through ducts and quasi-three-dimensional representation of volumes. Detailed modeling of individual components is included to specify the phenomena in the singular components. References Abagnale C., Cameretti M.C., De Simio L., Gambino M., Iannaccone S., Tuccillo R. (2014). "Numerical Simulation And Experimental Test Of Dual Fuel Operated Diesel Engines". Applied Thermal Engineering, vol. 65, 2014, p. 403-417  Abagnale C., Cameretti M.C., Ciaravola U., Tuccillo R., Iannaccone S., (2015). Dual Fuel Diesel Engine at Variable Operating Conditions: A Numerical and Experimental Study. In: SAE Technical paper 2015-24-2411. SAE TECHNICAL PAPER, vol. 1  Cameretti M.C., Ciaravola U., Tuccillo R., Iannaccone S., L.De Simio, (2016). A NUMERICAL AND EXPERIMENTAL STUDY OF DUAL FUEL DIESEL ENGINE FOR DIFFERENT INJECTION TIMINGS. APPLIED THERMAL ENGINEERING journal.