7. Dilution Effect on the Propagation and Extinction of Lean Premixed Syngas/Air Flames

The dilution effects of inert components N₂ and CO₂ on the propagation and extinction of lean premixed H₂/CO/air syngas flames were experimentally and numerically investigated. It was found that CO₂ dilution had more profound effect on flame propagation and extinction than N₂ dilution. The three effects, probably caused by the presence of CO₂ and N₂ diluents, namely the thermal effect, the diffusivity change effect and the chemical effect, and their preferential importance were numerically assessed. The thermal effect dominated the overall dilution effect in reduction of laminar flame speed and extinction strain rate. The chemical effect caused by CO₂ dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change effect is negligible for both CO₂ and N₂ diluents. N₂ only act as a thermal inert in the propagation and extinction of the H₂/CO/air flames.