Further development of the three-region model of a premixed turbulent flame II. Instability dominated region 1

Abstract

An analysis of the balance equation for turbulent kinetic energy of an instability dominated region 1 is presented for a turbulent, premixed propane-air flame. The effects of intensity, scale and laminar burning velocity on the energy balance are also examined. Specifically, the nature of instability in a turbulent flame and its influence on the flame structure are highlighted. These results show that either increase in scale or reduction in intensity of approach turbulence increases the magnitude of all the terms in the balance equation. The core region of the flame is unaffected by a small scale instability, whereas, for a large scale instability, the ratio of turbulence production/viscous dissipation remains independent of scale. The dominant terms in the energy balance are found to be those of convection and advection when the structure of the flame turbulence consists mainly of a large scale fluctuating motion. Finally, increase in laminar burning velocity restores stability and causes transition to region 2, in which production and viscous dissipation predominate over convection and advection terms, respectively.