Development of Ultra-Micro Combustor Using Cylindrical Flames

Abstract

The purpose of this study is to develop an ultra-micro combustor that uses two types of coaxial cylindrical flames, rich premixed flame and diffusion flame. The combustor consists of inner and outer porous tubes, and rich propane-air mixture and air issued, respectively, through the inner tube outwardly and through the outer tube inwardly, forming a cylindrical stagnation plane sandwiched by the inner rich premixed flame and the outer diffusion flame. Petal type flame was also observed in the downstream of the cylindrical flames. Keeping the equivalence ratio φ_i and flow rate q_i of the rich mixture constant, air flow rate q_a was varied. The O₂ and CO concentrations and temperature of the burnt gas were measured, and heat loss rate η_hl and combustion intensity L were evaluated. The obtained results are described as follows. (1)The relation curve of η_hl with the overall equivalence ratio φ_all, which is evaluated from the total flow rate of the fuel and the air, has a minimum value. (2)The relation curve of the minimum value of η_hl with L has a minimum value. (3) The CO concentration of the burnt gas increases as q_a is increased because of local extinction of the petal type flame. (4)When q_a is increased further, petal type flame is also extinguished. After that, the O₂ concentration increases and the CO concentration decreases.