Bioethanol – gasoline fuel blends: exhaust emissions and morphological characterization of particulate from a moped engine

This study was aimed at evaluating the effects of gasoline-ethanol blends on the exhaust emissions in a catalyst-equipped four-stroke moped engine. The ethanol was blended with unleaded gasoline in at percentages (10, 15, and 20% v/v). The regulated pollutants and the particulate matter emissions were evaluated over the European ECE R47 driving cycle on the chassis dynamometer bench. Particulate matter was characterized in terms of total mass collected on filters and total number of particles in the range 7 nm-10 μm measured by electrical low-pressure impactor (ELPI). In addition, particle-phase polycyclic aromatic hydrocarbons (PAHs) emissions were evaluated to assess the health impact of the emitted particulate. Finally, an accurate morphological analysis was performed on the particulate by high-resolution transmission electron microscope (TEM) equipped with a digital image-processing/data-acquisition system. In general, CO emission reductions of 60-70% were obtained with 15 and 20% v/v ethanol blends, while the ethanol use did not reduce hydrocarbon (HC) and NO x emissions. No evident effect of ethanol on the particulate mass emissions and associated PAHs emissions was observed. Twenty-one PAHs were quantified in the particulate phase with emissions ranging from 26 to 35 μg/km and benzo[a]pyrene equivalent (BaPeq) emission factors from 2.2 to 4.1 μg/km. Both particulate matter and associated PAHs with higher carcinogenic risk were mainly emitted in the submicrometer size range (<0.1 μm). On the basis of the TEM observations, no relevant effect of the ethanol use on the particulate morphology was evidenced, showing aggregates composed of primary particles with mean diameters in the range 17.5-32.5 nm. Implications: Mopeds may contribute in a large share to air pollution in some major urban areas; therefore, efforts may be taken to reduce their emissions. The addition of ethanol into gasoline (up 20% v/v) leads to a significant reduction of CO emission at the exhaust of a catalyzed 4-S moped, whereas this does not reduce HC and NOx. No clear effects on particulate matter and associated PAHs emissions have been observed with ethanol addition, but particulate-phase PAHs were mainly found on submicrometer-size particles (< 0.1 μm), which penetrate deeply into the human respiratory tract.