An experimental study was performed to investigate the effect of fuel composition on combustion, gaseous emissions, and detailed chemical composition and size distributions of diesel particulate matter (PM) in a modern heavy-duty diesel engine with the use of the enhanced full-dilution tunnel system of the Engine Research Center (ERC) of the UW-Madison. Detailed description of this system can be found in our previous reports [1,2].The experiments were carried out on a single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system. The operating conditions of the engine followed the California Air Resources Board (CARB) 8-mode test cycle. The fuels used in the current study include baseline No. 2 diesel (Fuel A: sulfur content = 352 ppm), ultra low sulfur diesel (Fuel B: sulfur content = 14 ppm), and Fisher-Tropsch (F-T) diesel (sulfur content = 0 ppm).Samples were collected on a series of teflon and baked quartz fiber filters to evaluate mass loading, elemental and organic carbon (EC/OC), sulfates (SO42-), and trace metals for the three different fuel compositions. A scanning mobility particle sizer (SMPS) was used to measure particle number concentrations and size distributions.Results show that the fuel composition significantly affected combustion, mass loading, chemical composition, and number concentrations and size distributions of PM. Mass loading, EC, and sulfates were significantly lowered with the advanced diesel fuels (Fuel B and F-T fuel) at higher loads. The advanced diesel fuels also produced more nuclei-mode particles and less accumulation-mode particles than Fuel A at high load conditions. In contrast, the former produced less nuclei-mode particles and more accumulation-mode particles than the latter at the medium load conditions.