SPECIATION OF PARTICULATE-ASSOCIATED PAH EMISSIONS IN A DIESEL SINGLE-CYLINDER ENGINE USING A HPLC-UVD METHOD

Polynuclear or polycyclic aromatic hydrocarbons (PAH) are known to be one of the most dangerous hydrocarbons due to their carcinogenic potential. Some PAH have been measured and regulated in the atmosphere to quantify the air quality. However, in order to better understand the presence of these compounds in the atmosphere, it is also important to study the PAH sources. In this paper, the particulate-associated PAH emissions from a single-cylinder diesel engine and their carcinogenic potential are analyzed. The engine was tested with a Spanish typical diesel fuel (with a 5.8 % wt of biodiesel), varying the injected fuel mass, the injection pressure and the intake air pressure. In order to study the method accuracy, and given that it is pretended to study subsequently in depth the effect of different injection strategies on the engine performance and its emissions, it has been chosen these three parameters as relevant in this study. With these parameters, the air-fuel mixing is changed and, therefore, the combustion process and efficiency. Sampling was carried out using fiber-glass filters in a dilution mini-tunnel, extracting the trapped PAH using Soxhlet extraction for 16 h with dichloromethane/methanol (7:3). Liquid chromatography with ultraviolet-visible detection was used for speciation, whose operating times are shorter than those of gas chromatography. In the present method, acetonitrile and water were used as solvents for 50 min. Results showed that PAH emissions are strongly dependent of intake air pressure, being much higher when the pressure increased. This is explained by the relative air-fuel ratio, which increases strongly with the air pressure, as more air mass is introduced in the process. Due to this, the thermal level of the process decreases. The chamber temperature reached lower levels with the air pressure increase, as the thermal diagnosis showed. In this case, the released energy is used to heat both the extra air and the fuel. This trend is also observed when this ratio changes when varying the fuel mass, being PAH emissions higher with the lower value. However, as the temperature and pressure variations depended on the fuel increase, which was lower, these differences were not as significant as in the first case. As for the injection pressure, results were not conclusive, as it appeared a maximum of emission in the middle test point. Finally, carcinogenic potential (KE) seemed not to be totally related to specific emissions, as its calculation depended on the toxic equivalence factors (TEF), which change in a logarithmic scale.