Preferential diffusion effects on flame characteristics in H2/CO syngas diffusion flames diluted with CO2

Numerical study is conducted to clarify preferential diffusion effects of H2 and H on flame characteristics in synthetic diffusion flames of the compositions of 80% H2/20% CO and 20% H2/80% CO as representatively H2-enriched and CO-enriched H2/CO flames. Impacts of CO2 addition to the flames are also examined through the variation of added CO2 mole fraction from 0 to 0.5. A comparison was made by employing a mixture-averaged diffusivity and the suppression of the diffusivities of H and H2. It is found that preferential diffusion effects on maximum flame temperature cannot be explained by the well-known behavior between maximum flame temperature and scalar dissipation rate but by chemical processes. The concrete evidence is also presented through the examination of the behavior of maximum H mole fraction and the behavior of importantly-contributing reaction steps to overall heat release rate.