Carbonyl compounds emitted by a diesel engine fuelled with diesel and biodiesel–diesel blends: Sampling optimization and emissions profile

Abstract

Biodiesel is emerging as a renewable fuel, hence becoming a promising alternative to fossil fuels. Biodiesel can form blends with diesel in any ratio, and thus could replace partially, or even totally, diesel fuel in diesel engines what would bring a number of environmental, economical and social advantages. Although a number of studies are available on regulated substances, there is a gap of studies on unregulated substances, such as carbonyl compounds, emitted during the combustion of biodiesel, biodiesel– diesel and/or ethanol–biodiesel–diesel blends. CC is a class of hazardous pollutants known to be participating in photochemical smog formation. In this work a comparison was carried out between the two most widely used CC collection methods: C18 cartridges coated with an acid solution of 2,4-dinitrophenylhydrazine (2,4-DNPH) and impinger bottles filled in 2,4-DNPH solution. Sampling optimization was performed using a 22 factorial design tool. Samples were collected from the exhaust emissions of a diesel engine with biodiesel and operated by a steady-state dynamometer. In the central body of factorial design, the average of the sum of CC concentrations collected using impingers was 33.2 ppmV but it was only 6.5 ppmV for C18 cartridges. In addition, the relative standard deviation (RSD) was 4% for impingers and 37% for C18 cartridges. Clearly, the impinger system is able to collect CC more efficiently, with lower error than the C18 cartridge system. Furthermore, propionaldehyde was nearly not sampled by C18 system at all. For these reasons, the impinger system was chosen in our study. The optimized sampling conditions applied throughout this study were: two serially connected impingers each containing 10 mL of 2,4-DNPH solution at a flow rate of 0.2 L min 1 during 5 min. A profile study of the C1–C4 vapor-phase carbonyl compound emissions was obtained from exhaust of pure diesel (B0), pure biodiesel (B100) and biodiesel– diesel mixtures (B2, B5, B10, B20, B50, B75). The SCC of the emission concentrations were 20.5 ppmV for B0 and 15.7 ppmV for B100. When considering fuel blends, the measured SCC were 21.4 ppmV, 22.5 ppmV, 20.4 ppmV, 14.2 ppmV, 11.4 ppmV and 14.7 ppmV, respectively, for B2, B5, B10, B20, B50 and B75. Among the target CC, both formaldehyde and acetaldehyde were the major contributors to the observed total CC levels. Except for acrolein and formaldehyde, all CC showed a clear trend of reduction in the emissions from B2 to B100 (40% reduction, on average). Both individual and total CC emission factors (pg g 1 of fuel burnt) were calculated for all tested biodiesel–diesel blends. The lowest total CC emission factor (2271 pg g 1) was found when B50 was used; the individual emission factors determined (pg g 1) were: 539.7 (formaldehyde), 1411 (acetaldehyde), 30.83 (acrolein), and 310.7 propionaldehyde).