Comprehensive analysis of toluene/ammonia-air premixed flame: Experimental and kinetic perspectives on laminar burning velocity

This study measured the laminar burning velocity (S_L) of a toluene/ammonia (A1CH₃/NH₃) mixture at an initial temperature (T_i) of 400 K, NH₃ mole fraction (X_NH3) ranging from 0 % to 70 %, and equivalence ratio (ϕ) ranging from 0.8 in to 1.4 in an atmospheric environment. The chemical mechanism of A1CH₃/NH₃ has been revised and developed using the authors' previous toluene reference fuel (TRF)/NH₃ mechanism. The reaction rate of the unimolecular decomposition reaction of A1CH₃ and phenol (A1OH) has been modified based on research data. Furthermore, the present model incorporates C-N cross reaction (H-abstraction reaction) of A1CH₃ and benzene (C₆H₆) when attacked by amine (NH₂). The new mechanism demonstrates strong agreement with the measured S_L of A1CH₃/NH₃ mixture in this study and in previous researches. Additionally, to enhance the application of NH₃ with various hydrocarbon fuels, the effect of NH₃ on isooctane (IC₈H₁₈) and A1CH₃ was compared. The results revealed a greater effect on A1CH₃ compared to IC₈H₁₈. To further elucidate the disparity between IC₈H₁₈ and A1CH₃ blends, a sensitivity analysis and reaction pathway analysis were also carried out. The results indicate that H-abstraction reaction of A1CH₃ has a more significant effect than IC₈H₁₈. Meanwhile, the reaction pathway indicates that the addition of NH₃ can promote H-abstraction of IC₈H₁₈ and A1CH₃. However, the effect on A1CH₃ was significantly greater than on IC₈H₁₈. The study also examined the effect of H-abstraction reaction on S_L. Numerous prior studies have demonstrated that H-abstraction reaction has a minimal effect on flame velocity. Nevertheless, this study has determined that H-abstraction reaction can have a significant effect on the flame velocity of an A1CH₃/NH₃ mixture, indicating that it should not be disregarded in the chemical kinetic model.