Characteristic of the premixed flame in a triple flame

Burning velocity and thermal diffusive structure of a triple flame generated with methane-air mixture are experimentally investigated in various fuel concentration gradients. The thermal diffusive width of premixed flame wing related preheat zone, which is measured from laser tomographic images, decreases by increasing the concentration gradient. On the other hand, burning velocity of the triple flame, which is measured from PIV, is almost constant. C. J. Sun et al. propose the theory on the burning velocity and preheat zone width, which takes into account the effect of flame curvature, strain and Le number. The burning velocity by their theory is smaller than the measured triple flame burning velocity and shows the tendency to decrease by increasing the concentration gradient. Similarly, the preheat zone width by their theory is larger than the measured thermal diffusive width of triple flame and is almost constant at any concentration gradients. Burning velocity along the premixed flame wing indicate the distribution of the flame temperature. These profiles and flame structure show the tendency that heat flux from non-premixed flame to premixed flame goes up by increasing the concentration gradient. Especially, the rich side heat flux is larger than lean side one. Because of this effect, the thermal structure of the premixed flame wing is changed and the burning velocity is kept constant by changing the concentration gradient. These results indicate that there exists the thermal interaction between the premixed and non-premixed flames at a leading edge of the triple flame. And non-premixed flame interacts with rich premixed flame stronger than lean premixed flame.