Abstract
The diffusion flames under the conditions of Re = O(1~2) and Fr >> 1 become spherical shape. Since the size of flames that satisfies the conditions is usually small, they are called microflame. As for microflame, the whole flame zone exists close to the burner tip, typically within a few mm. Such condition is quite different from other conventional burners.The effects of burner condition need to be examined for fundamental understanding of microflames and simulating droplet combustion. The effects of burner size and material on the lower extinction limit of methane diffusion microflame are measured by changing an inner diameter of burner outlet in the range from 0.7 mm to 4.3 mm and by using SUS 304 and copper burner. The burner with smaller thermal conductivity (SUS 304) shows lower fuel flowrate at the lower extinction limit. The lower extinction limit of fuel flowrate decreases with decreasing burner diameter, owing to the effect of smaller heat transfer cross-sectional area, which is more dominant than the effect of thermal conductivity and temperatures of fuel and burner.
