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The effect of the biodiesel feedstock on the engine performance and emissions is expected to become increasingly important as the emissions regulations become more stringent (Euro 5). This work aims to study the effect of the degree of unsaturation of a biodiesel fuel (which is a characteristic of the original oil), this being quantified by the iodine number, on the pollutant emissions and combustion timing. Four biodiesel fuels with iodine numbers ranging from 90 to 125 were tested pure and blended (30% and 70% biodiesel content, volume basis) with a diesel reference fuel, which was tested too, in a four-cylinder, 2.2 litre, turbocharged, direct injection diesel engine. The operation modes were selected to be representative of the New European Driving Cycle. In general, pure biodiesel fuels, compared to the reference fuel, resulted in sharp reductions in particle mass and opacity (60-70%) and in a slight increase in both fuel consumption (around 15% in mass) and NOx emissions (9%).

Methyl esters obtained from the most interesting Spanish oleaginous crops for energy use -sunflower and cynara cardunculus- were both used as diesel fuels in this work, pure and in 25% blends with a reference commercial fuel which was also used pure. A stationary engine test bed, together with the appropriate instrumentation for chemical and morphological analysis, allowed to evaluate the effect of these fuels on the engine emissions, particularly in the main particulate matter characteristics, such as soluble organic fraction, origin of adsorbed hydrocarbons, sulphate content, particle number per unit filter surface, and mean particle diameter. Both the consideration of the main thermochemical properties of the tested fuels and the computations of a chemical equilibrium model were helpful for the analysis of the experimental results.

Regulated gaseous emissions and particle concentrations, with commercial diesel fuel, animal fat biodiesel and gas to liquid (GTL) fuel from a Low Temperature Fischer-Tropsch process, have been studied. Tests were carried out in a light duty vehicle (Nissan Qashqai, 110 kW, Euro 4) equipped with variable geometry turbocharger (VGT), cooled exhaust gas recirculation (EGR), common rail with split fuel injection strategy, diesel oxidation catalyst (DOC) and diesel particle filter (DPF). Vehicle tests were carried out at real-world driving conditions. Specific emissions, in g/km, were determined separately for two test circuits (urban and extraurban). Results show that the use of alternative fuels reduced THC and CO emissions compared to diesel fuel while only slight differences were observed in NOx emissions and in particle number concentration.