Assessment of extended HyChem-based gasoline kinetic mechanisms for soot production in coflow diffusion flames

Accurate prediction of soot formation remains a challenge in thermal systems involving hydrocarbon combustion. This work presents a case study on the extension and evaluation of gasoline combustion reaction mechanisms for soot-forming diffusion flames, using kinetic models and computational tools commonly employed in thermal engineering applications. Four extended reaction mechanisms were constructed based on the HyChem Shell D gasoline model by incorporating a polycyclic aromatic hydrocarbon (PAH) sub-mechanism developed by Slavinskaya et al. The proposed mechanisms include both skeletal and detailed formulations, as well as optimized variants aimed at improving predictive performance. Results were compared against experimental data in two stages: first, the impact of the extensions on fundamental combustion properties was evaluated through laminar flame simulations using Cantera; second, the mechanisms were applied to a laminar gasoline coflow diffusion flame simulated with the CoFlame code to examine their ability to reproduce flame structure, temperature fields, and soot volume fractions. The results show that direct incorporation of PAH chemistry can significantly alter predicted thermal and combustion characteristics, leading in some cases to lifted flames, elevated peak temperatures, and reduced soot levels. Among the mechanisms tested, the optimized skeletal-based model provided the best compromise between computational cost, flame-structure prediction, and soot prediction, whereas adjustment of the detailed/reduced model mainly improved laminar flame speed with minor impact on soot formation. This case study highlights the importance of careful mechanism selection and validation when modeling sooting flames and offers practical guidance for engineers performing numerical analyses of combustion-driven thermal systems.