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In order to reduce the pollutant emissions (NOx and PM) of diesel engines, the addition of small gaseous fuel amounts or dual mode operation have been proved as potential techniques. This paper is focused on a detailed characterization of the particles emitted from a single cylinder diesel engine when part of the diesel fuel (5 to 20% by energy) is replaced by a gaseous fuel (producer gas, mainly composed by H2, CO, CH4 and inert compounds) coming from biomass steam gasification. The engine was run at constant speed and torque and different EGR rates. Particle samples were collected by means of fiber glass filters placed in a dilution mini-tunnel. Simultaneously, during tests, part of the exhaust gas was conducted to an SMPS to determine the particle size distribution.

The work has been focused on the measurement and analysis of the main Diesel emissions from an automotive Diesel engine mounted in a test bench prepared for operating in different transient sequences. The engine was fuelled with a conventional fuel and an emulsified fuel. A commercial pure low sulphur diesel fuel and an emulsified fuel (water in oil, w/o) with 5% v/v of water, were used as test fuels. A smoke meter and a gaseous emissions analyser allowed for the study of the effect of these fuels on the Diesel emissions under the different operating transient sequences. The properties of the test fuels and the time-recording of some engine parameters, such as fuel/air ratio or exhaust gas recirculation ratio, were used for the analysis and interpretation of the results.

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.