Experimental and numerical investigation on the near flammability limits behavior of syngas/air mixtures: effect of H2/CO ratios and inert gas additions

To promote the safe application of syngas (H₂/CO), the flammability limit parameters of syngas under varying H₂/CO ratios, along with the effects of inert gases (N₂, CO₂) on these limits and the explosion triangle, are investigated. Additionally, the chemical kinetic behavior near the lower flammability limit (LFL) of syngas is analyzed. The findings reveal that increasing the H₂ proportion in syngas significantly lowers the LFL and elevates the explosion hazard level. The introduction of inert gases notably reduces the upper flammability limit (UFL) and the explosion hazard level of syngas. As the H₂ proportion increases, the syngas explosion triangle expands and shifts toward the lower left, thereby reducing the non-explosive region area. The chemical kinetics near the LFL of syngas demonstrates increasing the volume ratio of H₂ in syngas can accelerate the generation rate of key free radicals, promote the generation of O and OH free radicals more rapidly, but intensify the inhibition of the generation of H free radicals. Among these, the elementary reactions R1, R3, R4, R5, R15, and R32 are identified as the most critical factors affecting the likelihood of syngas explosion. Adding appropriate inhibitors targeting these key elementary reactions can, to a certain extent, suppress the explosion of syngas. These findings provide valuable references and a foundation for enhancing the safe utilization of syngas.