Resumen de Caracterización e implicaciones atmosféricas de emisiones de motores diesel con biocombustibles.
Araceli Tapia Valle
The climate change it has revealed as the main atmospheric pollution problem at present. Some of the compounds that are directly implicated in the generation of this problem are emitted from mobile sources as a result of the combustion processes of fossil fuels in vehicles. For this reason it is necessary to use new energetic sources less pollutant than fossil fuel as hydrogen, biomass, biofuels, etc.. But before installing a new energetic source, it is necessary to study its viability from different points of view as the economic, energetic performance and the environmental impact. In this sense, the present work studies the effect of different biofuels on the unregulated exhaust emissions from a diesel engine. Traditionally the legislation establishes the emission limit levels of the regulated compounds as the total hydrocarbons, CO2, NOx and particulate matter, but furthermore the implications of these compounds in the atmospheric reactivity must be considered. Specifically, the volatile organic compounds (VOCs) are heavily involved in key atmospheric processes and play a central role in the chemical processes that determine the oxidizing capacity of the atmosphere. Firstly this study has been centered in the identification and quantification of VOCs proceeding from the combustion of fuels with different chemical compositions as diesel, eb-diesel and 100% rapeseed biofuel. Preconcentration techniques as adsorption on Tenax and derivatization with 2,4-DNPH have been used and GC-MS and HPLC as analysis techniques. After comparing the influence of the oxygen content in each fuel in the emissions of alkanes, alkenes, ketones, aromatic compounds, alcohols and aldehydes, the atmospheric reactivity of some of these compounds has been studied in the laboratory. The kinetic behaviours of 3-methylfuran with OH and NO3 radicals and 2-furaldehyde, 3-furaldehyde and 5-methylfufural with Cl atoms have been studied at room temperature and atmospheric pressure using the relative technique to determine rate coefficients. For a better knowledge, furthermore, the products of the reaction of 3-methylfuran with OH and NO3 have been investigated using two analysis techniques, GC-MS joint with solid-phase microextraction (SPME) as preconcentration system and FTIR. Finally, in order to assess the measured VOCs emissions concerning the photochemical ozone production, the ozone formation potential has been calculated for the emissions of the different biofuels. It is confirmed that emission factors of alkanes, alkenes and aromatic compounds decrease at the same time that the oxygen content increases in the fuel, but acetaldehyde concentration increases in the eb-diesel emissions compared with diesel and 100% rapeseed biofuel which confers a higher capacity of ozone production on eb-diesel. The absolute rate coefficients obtained for OH and NO3 radical reactions with 3-methylfuran in units of cm3 molec.-1 s-1 are (1.13 ± 0.22) 10-10 and 1.28 10-11. On the other side the absolute rate coefficients obtained for Cl atom reactions with 2-furaldehyde, 3-furaldehyde and 5-methylfuraldehyde in units of 10-10 cm3 molec.-1 s-1 are (2.61 ± 0.27), (3.15 ± 0.27) and (3.96 ± 0.50). The OH and NO3 initiated oxidation of 3-methylfuran led to the formation of 1,4-dicarbonyl compounds such as 2-methylbutenedial and aldehydes such as 3-furaldehyde, ketones as 3-methyl-2,5-furanodione, 5-hydroxi-3-methyl-2(5H)-furanone and 5-hydroxi-4-methyl-2(5H)-furanone, and nitroperoxy compounds.
