Co-firing ammonia with other fuels is receiving growing interest as a feasible solution to improve its combustion and emission properties. Many experiments found that the addition of ammonia to conventional hydrocarbon fuels can significantly reduce polycyclic aromatic hydrocarbons (PAHs) and soot formations [1-3]. However, the mechanism of soot suppression by ammonia has not been fully understood yet. The measurements [3] in premixed flames showed that the chemical compositions of nascent soot particles are similar in both ethylene and ammonia/ethylene flames. Less than 3% of chemical species are nitrogen-containing in the ammonia-doped flames. Recently, the investigations of reaction pathways [4] found that although the rate constant for the addition of HCN to aromatic structures is close to that of C2H2 addition, it is highly reversible at high temperatures. Therefore, the direct chemical effect of doping ammonia on PAH formation is mainly to temporarily block the reaction sites to prevent further growth of PAHs through the hydrogen abstraction acetylene addition (HACA) pathway.

Numerical simulations can provide more detail to understand the phenomena observed in experiments. However, the majority of simulations underestimated the effects of ammonia on soot reduction [2, 5, 6], which were usually explained by the inaccurate predictions of PAHs in the ammonia-diluted flames. The experimental results [1] in ammonia/ethylene counterflow diffusion flames showed that the soot sensitivity to ammonia addition was much greater than that of PAHs. Therefore, the inception model, described the transition from PAHs to soot particles, transfers the PAHs sensitivity for ammonia addition to soot particles, and this model may important for the predictions of soot sensitivity to ammonia addition.