Particle Number, Size and Mass Emissions of Different Biodiesel Blends Versus ULSD from a Small Displacement Automotive Diesel Engine

Abstract

Experimental work was carried out on a small displacement Euro 5 automotive diesel engine alternatively fuelled with ultra low sulphur diesel (ULSD) and with two blends (30% vol.) of ULSD and of two different fatty acid methyl esters (FAME) obtained from both rapeseed methyl ester (RME) and jatropha methyl ester (JME) in order to evaluate the effects of different fuel compositions on particle number (PN) emissions. Particulate matter (PM) emissions for each fuel were characterized in terms of number and mass size distributions by means of two stage dilutions system coupled with a scanning mobility particle sizer (SMPS). Measurements were performed at three different sampling points along the exhaust system: at engine-out, downstream of the diesel oxidation catalyst (DOC) and downstream of the diesel particulate filter (DPF). Thus, it was possible to evaluate both the effects of combustion and after-treatment efficiencies on each of the tested fuels. Experiments were performed on a series of engine operating conditions, representative of specific phases of the New European Driving Cycle (NEDC), including cold start of the engine. No significant differences in terms of particle number were detected at engine-out among the different fuels under steady-state operating conditions, while a moderate reduction could be observed in particles mass size distribution with biofuels blends. Finally, the effects on PM emissions due to shifts of the engine operating points on the calibration maps caused by the different fuel characteristics (i.e. by the lower LHV of the biofuel blends) were shown to be extremely important, and significantly larger than the effects due to the different combustion characteristics of the biofuel blends, thus highlighting the need for a specific adjustment of the engine calibration in order to avoid jeopardizing the potential emission benefits of biofuels.