SURVIVAL OF POLYCYCLIC AROMATIC-HYDROCARBONS DURING DIESEL COMBUSTION

The application of a radiotracer technique to investigate the sources of polycyclic aromatic hydrocarbons (PAH) in diesel exhaust emissions is described.; In separate experiments, C-14-radiolabeled naphthalene, 2-methylnaphthalene (2-MeNp), fluorene, pyrene, and benzo[a]pyrene (B [a]P) were each added to diesel fuel, which was combusted in a 2-L dir ect injection Perkins Prima diesel engine. Exhaust samples were collec ted using a novel exhaust gas sampling device designed for sampling or ganic species in automobile exhaust emissions. Survivals for these PAH were 0.87% for fluorene, 0.54% far 2-MeNp, 0.47% for naphthalene, 0.1 7% for pyrene, and 0.04% for B[a]P. A linear relationship was observed between the extent to which individual PAH survived combustion and th e energy level of the lowest unoccupied molecular orbital (LUMO) of th e molecule. LUMO energy levels far each molecule were calculated from Huckel molecular orbital theory. The relationship observed in the curr ent experiment suggests that, for these PAH and under steady-state eng ine conditions, it is the chemical kinetics of reactions occurring in the combustion chamber as opposed to thermodynamic stabilities that de termine the extent of PAH survival during diesel combustion. Using thi s relationship, it should be possible to predict the extent of PAH sur vival in diesel emissions from a knowledge of the PAH composition of t he fuel.