Study of Polycyclic Aromatic Hydrocarbons Evolution Processing in GDI Engines Using TRF-PAH Chemical Kinetic Mechanism

In the present study, we developed a reduced TRF-PAH chemical reaction mechanism consisted of iso-octane, n-heptane and toluene as gasoline surrogate fuels for GDI (gasoline direct injection) spark ignition engine combustion simulation. The reduced mechanism consists of 85 species and 232 reactions including 17 species and 40 reactions related to the PAHs (polycyclic aromatic hydrocarbons) formation. The present mechanism was validated for extensive validations with experimental ignition delay times in shock tubes and laminar flame speeds in flat flame adiabatic burner for gasoline/air and TRF/air mixtures under various pressures, temperatures and equivalence ratios related to engine conditions. Good agreement was achieved for most of the measurement. Mole fraction profiles of PAHs for n-heptane flame were also simulated and the experimental trends were reproduced well. The vapor-phase and particulate-bound PAHs existed in GDI engine exhaust were sampled and analyzed by GC-MS. We implemented the GDI combustion CFD simulation using CONVERGE code coupling with the TRF-PAH mechanism to predict the combustion characteristics and PAHs evolution processing occurring in cylinder. Good agreements in in-cylinder pressures and PAHs emissions were obtained between experimental and simulated results under various engine operating conditions. The evolution of PAHs and associated small molecules like C₂H₂ and C₃H₃ in cylinder was analyzed, and the relationship between the temperature field distribution and the PAHs distribution was also analyzed. In summary, the TRF-PAH mechanism is suitable for PAHs evolution simulation in GDI engine combustion.