Influence of Ferrocene (Fe(C 5 H 5 ) 2 ) on Rich and Lean Methane/Air Flames: The Suppression and Enhancement Effect

The effect of ferrocene (Fe(C5H5)2) on rich and lean CH4/air flames was investigated numerically using a newly assembled coupled kinetic model, which was validated against reference data. The normalized burning velocity, flame temperature, free radical concentrations, and ignition‑delay times were analyzed over equivalence ratios of Φ = 0.5–1.2 at unburned gas temperatures of 298–473 K. The results show that ferrocene suppresses rich and stoichiometric flames effectively at low loadings, whereas in lean flames it first inhibits and then promotes combustion as the loading increases, with the enhancement becoming stronger in leaner mixtures. This dual behavior arises from the competition between the fuel contribution of ferrocene-borne hydrocarbons and the chemical inhibition of iron-containing intermediates, rather than from a simple fuel-addition effect. Reaction‑pathway analysis reveals that 93.0% of ferrocene decomposes to FeC5H5 in rich flames but only 16.1% in lean flames, where 81.6% is converted to C5H4O. Sensitivity analysis further identifies R2166 (Fe(C5H5)2 + O = FeC5H5 + C5H4O + H) as the key reaction whose role flips from suppression at Φ = 1.2 to enhancement at Φ = 0.5.