This paper provides a study of injection process in a research compression ignition engine fueled with Rapeseed Methyl Ester pure biodiesel and its blends by advanced optical diagnostics and 1D model. Experimental tests have been performed in an optical direct injection single-cylinder engine equipped with the Common Rail injection system of a real compression ignition engine. The injection strategies consisted of two events per cycle, the pilot and the main. The investigated conditions were representative of two engine operating points of the WLTC corresponding to two different engine speed and brake mean effective pressure values. The 2D visible imaging and the novel infrared (IR) technique have been applied to evaluate fuel spray parameters (i.e. penetration and cone angle) for liquid and vapor phases, respectively. Experimental results have been compared to data obtained with commercial diesel fuel available from previous authors' works, underlining the main differences. Furthermore, to improve biodiesel spray knowledge, 1D model for diesel jets has been suitably modified to analyze RME spray. The model has been set up via collected experimental data. Pure fuel and blends properties have been evaluated using REFPROP® software. Once the model has been validated, it has allowed to calculate the equivalence ratio along both the jet axis and radial direction, and the amount of vapor fuel over time. The modified 1D model presented in this study could be an advanced and effective instrument to study injection process in the modern engines fed with biofuel, supporting experimental activities in order to reduce time and costs.