This work is focused on the measurement and analysis of biodiesel emissions resulting from two commercial diesel engines derived from the same baseline engine. One of the engines was equipped with a rotary fuel injection pump electronically controlled. Another engine was equipped with a common-rail injection system. Both engines were tuned by the manufacturer with diesel fuel, and each of them was optimized with different exhaust gas recirculation (EGR) strategies. Both engines were tested under several transient conditions. A methyl ester obtained from unused sunflower oil was tested as diesel fuel, pure and blended with 30 and 70% of a commercial diesel fuel, which was also used pure. The engines were mounted in a test bench prepared for operating under transient conditions. An AVL 439 smoke meter and an Environnement gas analyzer allowed for the study of the effect of these fuels on the variations of the engine emissions with time. The consideration of the thermochemical properties of the tested fuels and the engine parameters, such as fuel/air ratio or EGR ratio, were used for the analysis of the results. The studied engine transient processes were (a) a load increase at constant engine speed and (b) an engine speed decrease at constant torque. The obtained results proved that the biodiesel effect on pollutant emissions during transient conditions depends upon the fuel injection system and EGR strategy used during the engine tuning.
An experimental method for the indirect determination of the light extinction efficiency of the exhaust gas emitted by diesel engines is proposed in this paper, based on the simultaneous measurement of spot opacity and continuous opacity, together with the double modelling of the associated soot concentration. The first model simulates the projection of a differently sized soot particle population enclosed in an exhaust gas sample on the filter of a spot opacimeter. The second one simulates the light extinction caused by the soot particles flowing in the exhaust gas stream in an online continuous opacimeter, on the basis of the Beer-Lambert law. This method is an alternative to other theoretical or semi-empirical complex methods which have proved to be inadequate in the case of soot agglomerates. The application of this method to a set of experimental smoke measurements from a commercial light-duty DI diesel engine typical of vehicle road transportation permitted us to draw conclusions about the effect of different engine conditions on the mean light extinction efficiency of the soot particles flowing in the raw exhaust gas stream.
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