Abstract
The detailed behaviors of gaseous and spray lifted flames are studied by two- dimensional direct numerical simulations (DNS), and the characteristics of the flamelets are investigated in terms of two key variables for flamelet modeling, namely mixture fraction and scalar G. The results show that both the gaseous and spray lifted flames are partially premixed flames, in which premixed and diffusion flames co-exist and the premixed flame stabilizing the flames precedes to the diffusion flame. The non-combusting and combusting regions can be generally discriminated by the scalar G, and the premixed and diffusion flames in the combusting region can be predicted by flame index, respectively. Although the flamelets in the diffusion flame of the gaseous lifted flame are characterized by the mixture fraction and scalar dissipation rate, those on the spray lifted flame are not. To account for the flamelet characteristics of the spray lifted flame, flamelet/progress-variable approach needs to be introduced.
