Development of a chemical kinetic mechanism for ammonia/macromolecular hydrocarbon combustion

C-free fuel ammonia has a high auto-ignition temperature and low flame speed compared to conventional hydrocarbon fuels, which limits its application in internal combustion engines (ICEs). Blending ammonia (NH3) with a highly reactive fuel can effectively solve this problem, and traditional macromolecular hydrocarbon fuels are a good choice because of their practicality and economy. However, the chemical reaction mechanism for the combustion of NH3/macromolecular hydrocarbons is not yet fully understood. In this study, a detailed kinetic mechanism for NH3 and toluene reference fuel (TRF) is proposed with 250 species and 4272 reactions. The developed NH3/TRF mechanism was validated by a single component (NH3, n-heptane, iso-octane, and toluene) and multiple components (NH3/n-heptane, NH3/iso-octane, NH3/toluene) with ignition delay time, laminar burning velocity, and key intermediate component distribution. The current NH3/TRF mechanism showed good performance compared with previous mechanisms. The co-combustion of NH3/TRF blends was performed with different NH3 energy fractions, and sensitivity and reaction pathway analyses were performed to reveal the effect of TRF addition on NH3 combustion. The results showed that the OH radical is mainly produced through N-containing reactions rather than C-containing reactions under T = 1000 K, P = 40 atm, and ϕ = 1 with more than 30 % NH3 addition. The HO2 radical is the most important radical for NH3 ignition, in addition to OH radicals, and its reactions with N-containing radicals (NH2, H2NO, and NO) contribute to the majority of OH radicals.