2010 Volume 76 Issue 772 Pages 2258-2263
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, air flow rate q_a was varied. The O_2 and CO concentrations and temperature of the burnt gas were measured, and heat loss ratio 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 have 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 extinguished. After that, the O_2 concentration increases and the CO concentration decreases.