Among the new combustion concepts envisaged to meet future regulations, the Dual Fuel (DF) concept is considered to be an attractive strategy due to its potential to reduce CO2 emissions and engine-out pollutant emissions levels. A small quantity of high-cetane fuel (Diesel) is injected in the combustion chamber in order to ignite a homogeneous mixture of air and a highly volatile fuel (gasoline in our study). The DF concept has been shown to achieve improved engine thermal efficiency and low engine-out NOx and soot emissions. However, the physical mechanisms controlling DF combustion and in particular, determination of the predominant combustion regime(s) are not yet well understood. In this study, numerical simulations (CFD) and optical engine measurements are used to investigate Dual Fuel combustion. The ECFM3Z combustion model (implemented in the IFP-C3D code) is presented in this paper in addition to preliminary results which have been performed for DF internal combustion (IC) engine simulations. The approach employed in this study allowed determination of the relative contributions of auto-ignition (AI), flame propagation (ECFM) and Burned Gas (BG) to the total heat release and combustion development in terms of the spatio-temporal evolution throughout the engine cycle. The objective is first of all to evaluate the capacity/potential of existing models to cope with the various combustion regimes that might exist in DF combustion strategies and in particular transitions between different combustion modes. Results of preliminary experiments on a single cylinder optical engine are also reported in this paper. The objective was to apply advanced optical diagnostic techniques to characterize in detail the DF combustion process and provide an improved understanding of this novel combustion strategy and ultimately aid CFD model further developments.