This paper is a contribution to the understanding of the formation and oxidation of soot in Diesel combustion. An ECN spray A injector (single axial-oriented orifice) was tested in a well characterized high-temperature/high-pressure vessel at engine relevant conditions. The size of the test section (>70mm) enables to study the soot formation process in nearly free field conditions, which constitutes an ideal feature for fundamental understanding and model validation.Simultaneous high-speed OH* chemiluminescence imaging and high-speed 2D extinction were performed to link together the information regarding flame chemistry (i.e. lift-off length) and the soot data.The experiments were carried out for a set of fuels with different CN and sooting index (Diesel fuel, Jet fuel, gasoline and n-dodecane) performing parametric variations in the test conditions (ambient temperature and oxygen concentration).The methodology proposed allowed a qualitative evaluation of the main fuel characteristics affecting soot formation in Diesel combustion identified as Cetane Number (CN) and threshold sooting index (TSI). The experiments enabled the characterization of properties depending on these two features, and therefore a fuel characterization at engine relevant conditions.For CFD soot modeling purposes, three surrogate fuels were designed to mimic the behavior of the practical fuels tested matching their CN and TSI. The characterization methodology was used to validate/correct the surrogates’ composition in order to correctly reproduce the behavior of the practical fuels.The fuel characterization methodology, the experimental data gathered as well as the composition of the validated fuel surrogate for soot modeling at typical Diesel conditions are considered three major outcomes of this work.