Development of a PAH (polycyclic aromatic hydrocarbon) formation model for gasoline surrogates and its application for GDI (gasoline direct injection) engine CFD (computational fluid dynamics) simulation

To elucidate the evolution process of PAHs (polycyclic aromatic hydrocarbons) in GDI (gasoline direct injection) engines, a reduced chemical model with 17 species and 40 reactions for PAHs formation was developed and integrated into a skeletal TRF (toluene reference fuels) oxidation mechanism to predict PAHs emissions. The final mechanism consisted of 85 species and 232 reactions. The new mechanism was validated for ignition delays and laminar flame speeds for gasoline/air and TRF/air mixtures under engine-like conditions, and good agreement was obtained for most of the experiments. Laminar premixed flames were simulated to validate the small species related to PAHs formation, as well as PAHs profiles up to A4 in flames, and the experimental trends were reproduced well. The combustion processes of GDI engines can be reproduced well using the new mechanism. PAHs were sampled from exhaust and analyzed by GC–MS, and PAHs with more than four rings were primary observed in particulate matter, while two and three ring polyaromatic hydrocarbons mainly existed in the vapor-phase PAHs. The vapor-phase PAHs released from the exhaust pipe were predicted, and the results indicated that the current mechanism could be used as a valuable tool to meet the needs of CFD (computational fluid dynamics) simulation for PAHs evolution in GDI engine combustion.

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