Abstract: The present investigation describes the effect of methane addition to diesel fuel in dual fuel mode for direct injection CI diesel engine. The engine was simulated using Computational Fluid Dynamics (CFD) software. The mesh has been generated using “Meshing” code included in the software and combustion process has been analyzed using “Fluent” program. The simulation carried out using neat diesel fuel and dual (0.4 methane/0.6 diesel by mass) mixture at 1500 rpm and full load operation. The total mass fuel was injected to the cylinder in three stages. The simulation outputs such as heat release rate, maximum in-cylinder pressure, maximum in-cylinder temperature and penetration length were used to evaluate the effect of the alternative fuel addition and multiple-injection approach on the combustion process performance. The progress of the combustion process has been monitoring by recording the temperature distribution inside the combustion chamber during the simulation. The results showed that the addition of 0.4 mass fraction of methane to diesel fuel in CI engine gave an increase in the peak in-cylinder pressure, the peak heat release rate, the maximum in cylinder pressure and penetration length compared to neat diesel fuel operation due to higher flame propagation and fast combustion process of methane. Conversely, the methane combustion presented longer auto-ignition delay compared to neat diesel fuel. The simulation results showed good agreement with the experimental outcomes from the literature.