Development of ultra-micro combustor using cylindrical flames

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 φ1 and flow rate q1, of the rich mixture, air flow rate qa was varied. The O2 and CO concentrations and temperature of the burnt gas were measured, and heat loss ratio ηhl and combustion intensity L were evaluated. The obtained results are described as follows. ( 1 ) The relation curve of ηhl with the overall equivalence ratio φlt;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 ηhl with L have a minimum value. (3) The CO concentration of the burnt gas increases as Qa is increased because of local extinction of the petal type flame. (4) When Qa is increased further, petal type flame is extinguished. After that, the O2 concentration increases and the CO concentration decreases.