Detailed chemical effects of ammonia as fuel additive in ethylene counterflow diffusion flames

Abstract

Ammonia is considered one of the most competitive fuels due to its carbon neutrality. The chemical effects of NH3 are distinguished by kinetic analysis via adding NH3 as reactive NH3 and fictitious inert NH3. The flame temperature and the mole fraction profiles affected by the chemical effects of NH3 addition for important species and soot are analyzed, with special emphasis on soot and its important precursor polycyclic aromatic hydrocarbons (PAHs). The results illustrate that NH3 addition inhibits the production of A1-A4. The chemical effects of ammonia decrease the hydrogen abstraction–C2H2–addition (HACA) surface growth rate and PAH condensation rate, which further reduces soot volume fraction and average particle diameter D63. The ammonia decomposition pathways interact with ethylene decomposition pathways via the four reactions: NH3 + C2H5 = C2H6 + NH2, HCN + C2H5 = C2H6 + CN, NH2 + C2H4 = C2H3 + NH3, and CH2CH2NH2 = C2H4 + NH2. The dilution and thermal effects of NH3 are dominant effects on soot reduction, while the chemical effects further inhibit soot formation.