Lifting Mechanism of Inverse Diffusion Flames.

Numerical computations of the inverse diffusion flame were conducted to investigate the flame structure at the upstream end of the diffusion flames adjacent to the burner rim and to make clear the mechanistic difference of the flame lifting between inverse and normal diffusion flames. The results obtained are as follows. (1) The upstream end of the diffusion flame is located at the air side near the nozzle rim and consequently the air velocity instead of the fuel velocity is sensitive to the flame lifting. This fact explains the characteristic difference of the flame lifting of the inverse and normal diffusion flames. (2) The flame structure of the upstream end of the diffusion flame consists of the diffusion flame structure in the radial direction together with the premixed flame structure in the axial direction. (3) It is estimated that the burning velocity of the premixed flame formed at the upstream end of the diffusion flame is considerably low as compared with that of the one-dimensional premixed flame because of the heat loss induced in the radial direction and the flame holding is attributed to the balance of the fluid velocity and burning velocity.