In a context of a fossil reserve depletion and reduction of greenhouse gases (GHG) emissions, the search for new energy for transport is fundamental. Among those new energies, alternative fuels and especially synthetic fuel from Fischer-Tropsch process (so-called XtL, "X-to-Liquid" fuels) seem to have an interesting potential in terms of availability and GHG emission reduction, according to the feedstock used.Due to the special properties of such products, especially high cetane number, several strategies of incorporation can be envisaged: as a blend in specific basestocks in order to obtain a conventional fuel or a premium fuel or as a pure component. In order to assess these strategies; a standard diesel fuel (B0), a blend with 40%vol of Fischer-Tropsch and a neat Fischer-Tropsch have been tested on a modern downsized high pressure direct injection single-cylinder diesel engine. The used Fischer-Tropsch fuel is a commercial GtL - Gas to Liquid, with a cetane number higher than 80.First, engine tests have been performed with the same engine settings than the B0 fuel in order to evaluate the impact of the fuel formulation on the combustion behavior and on the engine outputs. Then, the engine settings were optimized for each fuel in order to achieve the best engine outputs, and so, evaluate the intrinsic performance of the tested fuels.This study allows understanding the influence of high auto-ignition fuels with low aromatic content on pollutant emissions at low speed/low load conditions (1500 rpm 3 bar of IMEP) and also on performances at full load. Without a dedicated calibration, the Fischer-Tropsch-based fuels induce a noticeable modification of the combustion process and engine outputs. The full potential of such fuels can only be achieved after a dedicated optimization of engine settings. This optimization enables to reduce HC and CO emissions at low speed/low load and increase the effective power at full load thanks to a smoke emission decrease.Some of these tests have received funding from the European Community's FP7 under grant agreement n° 218890 "OPTFUEL."