The lower flammability limit (LFL) of syngas/NH3/air mixtures was investigated using a 5 L explosion vessel and molecular dynamics simulations. Results indicate that the LFL decreases continuously with increasing syngas fraction and hydrogen content. A prediction model based on Le Chatelier’s formula was established and validated with high accuracy. Mechanistically, simulations reveal that adding syngas reduces specific heat capacity while enhancing thermal conductivity and diffusivity, thereby lowering the LFL. Higher syngas or hydrogen content significantly reduces the apparent activation energy of ammonia (e.g., decreasing from 78.84 to 38.85 kJ/mol), promoting reactivity. Notably, syngas addition is found to effectively reduce fuel residue, with the minimum observed at 60% syngas and 50% hydrogen content. Furthermore, the specific evolution behaviors of key species near the LFL were identified: H radicals increase before near-complete consumption; O and OH radicals initially rise and subsequently oscillate, with notable OH residue; and NH2 is rapidly generated and consumed in the early stage. These findings provide critical theoretical guidance for the ignition assessment and safety control of syngas/NH3 blends.
Li et al. (Tue,) studied this question.