Numerical calculations of the dynamic behavior of hydrogen-air lean premixed flames due to intrinsic instability based on the detailed chemical reaction model

The dynamic behavior of hydrogen-air lean premixed flames due to intrinsic instability was numerically investigated by two-dimensional unsteady calculations of reactive flows. We used the compressible Navier-Stokes equations with the detailed hydrogen-oxygen combustion consisting of seventeen elementary reversible reactions of eight reactive species and a nitrogen diluent. We obtained the critical wavelength through the dispersion relation, which was closely related with the dynamic behavior of premixed flames due to intrinsic instability. To investigate the characteristics of dynamic behavior, the disturbance with the critical wavelength was superimposed on premixed flames. The superimposed disturbance evolved owing to intrinsic instability, and then the cellular-flame front formed. With an increase in the space size, the burning velocity of a cellular flame became monotonously larger, which was generated by disturbances with long wavelengths. This indicated that the scale effect affected strongly the increase in the burning velocity. In addition, we found that the concentrations of hydrogen and hydroxyl radicals were high (low) in the downstream region of convex (concave) flame fronts with respect to the unburned gas. This was due to the diffusive-thermal effect. Moreover, we obtained the fractal dimension of flame fronts to elucidate the dynamic behavior of premixed flames. We revealed the scale effect on the burning velocity and the role of intermediate species in cellular flames to clarify the essence of intrinsic instability.