Effect of biodiesel on PAH, OPAH, and NPAH emissions from a direct injection diesel engine

Polycyclic aromatic hydrocarbon (PAH), oxy- and nitro-derivate PAH (OPAH and NPAH) emissions from a direct injection diesel engine fueled with conventional fossil diesel (D), waste cooking oil biodiesel (B100), and their two blends (B20 and B50) were compared. The results show that B100 can reduce low molecular weight PAHs such as naphthalene, acenaphthylene, and fluorene as much as 90% compared with diesel. However, the emissions of high molecular weight PAHs including benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[a]pyrene decrease slightly when using B100. The emission levels for PAHs and OPAHs present comparable, while NPAH emission levels are five to ten times lower than those of PAHs and OPAHs. Compared with diesel, PAH and NPAH emissions significantly decrease. On the contrary, an increase trend of OPAH emission has been observed with adding biodiesel. For the specific parent PAHs and its oxygenated and nitrated derivatives, the fractions of parent PAHs gradually decrease with increasing biodiesel content in the blends, while the corresponding oxygenated and nitrated derivative fractions observably increase, especially for the high molecular weight compounds. Considering the increase of OPAH and NPAH fractions in total particle-phase PAHs when using biodiesel, in-depth biodiesel cytotoxicity assessment should be conducted.