The effects of radiation on the dynamic behavior of cellular premixed flames generated by intrinsic instability

Abstract

Two-dimensional unsteady calculations of reactive flow on the basis of the compressible Navier–Stokes equation were performed to elucidate the effects of radiation on the dynamic behavior of cellular premixed flames generated by intrinsic instability. The disturbance superimposed on a planar flame evolved owing to hydrodynamic and diffusive-thermal effects, and then the cellular flame front formed. The dynamic behavior of cellular flames appeared at low Lewis numbers, and it became stronger as radiative heat loss increased. The island of the unburned gas surrounded by the burned gas was observed in non-adiabatic flames with low Lewis numbers. The average cell size of the non-adiabatic flame was slightly small compared with the adiabatic flame, even though the critical wavelength of the former flame was larger than that of the latter flame. This indicates that the radiation has a pronounced influence on the dynamics of premixed flames with low Lewis numbers. Owing to the dynamic behavior, the burning velocity of cellular flames changed drastically with time, which was due principally to the combination and division of cells. The average burning velocity of the non-adiabatic cellular flame was somewhat small compared with the adiabatic cellular flame. This is because that the burning velocity of planar flames decreases owing to radiation and that the dynamic behavior of cellular flames becomes stronger. In addition, the average burning velocity became larger monotonically as the length of computational domain increased. The reason is that the long wavelength components of disturbances play a significant role in the front shape of cellular flames.