Abstract
Diffusion microflames has potentials to be utilized as a point-symmetric one-dimensional flame to unveil detail structures of diffusion flame and as a heat source with high heat release density. The way to elevate those potentials is investigated in the present study. Thus, a microflame is established in the oxygen fraction controlled ambient coflow, where methane issues from the inner tube with 0.7 mm ID, whereas the coflow mixture of oxygen and nitrogen from the outer coaxial tube with 6.0 mm or 2.9 mm ID. The results show that increase of oxygen mole fraction in ambient flow makes a microflame close to the perfect point-symmetric one-dimensional flame. Specifically, increase of oxygen mole fraction from 0.21 to 0.49 reduces the difference from the perfect point-symmetric shape into half; this is considered because molecular diffusion becomes dominant owing to the decrease of Pe number resulting from the reduction of flame size. Increase of oxygen fraction is found to be quite effective to increase heat release density as it becomes 7 times larger by the increase of oxygen fraction from 0.21 to 0.49.
