Preferential diffusion effects in opposed-flow diffusion flame with blended fuels of CH4 and H2

Numerical study is conducted to clarify preferential diffusion effects of H2 and H in flame responses through the comparison among pure hydrogen, pure methane, and methane-hydrogen diffusion flames with detailed chemistry. The composition of fuel is systematically changed from pure methane to pure hydrogen through the molar addition of H2 to methane. A comparison was made by employing mixture-averaged species diffusion and the suppression of the diffusivities of H and H2. Discernible differences in flame responses with mixture-averaged species diffusion and the suppression of the diffusivities of H and H2 are displayed in those flames. The behaviors of maximum flame temperatures with the three species diffusion models are not explained by scalar dissipation rate (a physical process) but chemical effects. It is also seen that the preferential diffusion of H2 into reaction zone affects flame responses much larger than those through the preferential diffusion of H in diffusion flame. It is also shown that the behaviors of major chemical species with the three species diffusion models are also addressed to chemical effects through importantly contributing reactions to the production and destruction of those chemical species.