Soot Modeling of GTDI Engines Using a Recently Developed Turbulent Premixed Combustion Model Implemented with an Improved TRF Mechanism and a Practical Semi-Detailed Soot Model

In the present work, a practical semi-detailed soot model has been integrated with a recently developed turbulent premixed combustion model and an improved TRF (toluene reference fuel) chemical kinetic mechanism. The practical semi-detailed soot model includes a reduced PAH (polycyclic aromatic hydrocarbon) sub-mechanism, soot particle inception (or nucleation) through pyrene (A₄), C₂H₂-assisted and PAH-assisted surface growth, soot coagulation, and soot oxidation by both O₂ and OH. In the TRF mechanism recently improved by the author, eight dominant reactions for high-temperature operating conditions (T > 750 K) were identified and corrected. The turbulent premixed combustion model recently developed by the author includes a mechanism-dynamic-selection sub-model and a dynamic turbulent diffusivity sub-model in which Schmidt number is constructed as a function of local turbulence/thermodynamics conditions. The practical semi-detailed soot model including the reduced PAH sub-mechanism was validated after it was implemented into the improved TRF chemical kinetic mechanism using important species for soot formation from several premixed laminar burner-stabilized flames, as well as using flame lift-off length and spatial distribution of soot volume fraction from Sandia ECN (engine combustion network) data. Soot modeling of GTDI (gasoline turbocharged direct injection) engines was conducted using the integration (83 species and 336 reactions) of the soot model, the combustion model, and the TRF mechanism. The simulated soot mass from three GTDI engines/operating conditions can well capture the trend of soot flowing out of in-cylinder compared to the experimental data. Through CFD (computational fluid dynamics) analysis, the root-cause for major soot formation in GTDI engines is found. Based on the root-cause, an effective soot mitigation approach due to less soot formation and strong soot pulled back is presented.