Cellular instabilities of non-adiabatic laminar flat methane/hydrogen oxy-fuel flames highly diluted with CO₂

Cellular instability of non-adiabatic laminar premixed flat methane/hydrogen oxy-fuel flames highly diluted with CO₂ was studied systematically. The CH₄/H₂/CO₂/O₂ flames were stabilized on a McKenna burner at atmospheric pressure. The CH₄/H₂/CO₂/O₂ flames with varied equivalence ratios and hydrogen mole fractions were investigated. Quantitative structure parameters of the cellular flame fronts were obtained with OH-PLIF technique. On the basis of experimental results, theoretical analysis was made to clarify the effect of mixture properties and heat loss on flame cellular instability. Results showed that cellular flame structure appeared near the lean limit combustion condition. Cell number of flame and its hydrodynamic factor, ω_DL, present a positive correlation. The average stand-off distance, L, is well identified to characterize the cellular flames. Average cell amplitude, A, and wavelength, λ, increased with the increase of L. A good indicator of instability level, A·λ, was defined. The RS model was used in a linear stability analysis, and the onset of cellular flames was found to be governed by both hydrodynamic and thermal-diffusive instability mechanisms, while the heat loss made the flame more stable. The RS model is not an appropriate model to predict critical wavenumber for the non-adiabatic flame.