Flame interaction at leading edge of a triple flame regarded from the burning velocity

Upstream velocity field and curvature of a triple flame generated with methane-air mixture are experimentally investigated in various fuel concentration gradients. The flame curvature, which is measured from visible flame images, rises by increasing the concentration gradient. PIV data indicate that the triple flame burning velocity is almost constant. The flame strain rate goes up with the increase in concentration gradient. C. J. Sun et al. propose the theory on the burning velocity, 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. This result indicates that there is another effect which strengthens the burning intensity. The effect also cancels the others, which weakens the burning intensity. There is tendency for this effect to go up by increasing the concentration gradient. It suggests presence of the flame interaction between the premixed and non-premixed flames at a leading edge of the triple flame.