希薄燃焼に及ぼす水素添加の効果 : 第2報, 管状火炎の特性と輸送過程に及ぼす回転強さの影響

抄録

Lean combustion has the advantage of low pollutant emission levels, but its combustion rate is very low and the lean mixtures are difficult to ignite and form stable flames. To improve these disadvantages, we have focused on hydrogen addition to a premixed mixture. In this study, we have experimentally observed the characteristics of tubular flames for methane/air mixtures with hydrogen, and have investigated the effects of hydrogen addition on lean combustion in a swirling flow. We have measured the flame diameter, flame temperature and extinction limit, and tried to obtain the burning velocity. We have discussed the flame characteristics and transport process based on the flame and flow configurations. Results show that, as the concentration of added hydrogen is increased, (1) the flame diameter monotonically increases, (2) the fuel concentration at the extinction linearly decreases and effective equivalence ratio also decreases, (3) the radial temperature distribution becomes an M-shaped profile and the flame temperature increases, and (4) the burning velocity increases. As the rotational intensity is increased, these phenomena are more prominent. In a swirling flow, the pressure decreases around the rotational axis due to the centrifugal effects. The pressure gradient is formed, and there is mass transport due to pressure gradient (pressure diffusion), which changes kinetic process in flames. The reaction rate is changed through these phenomena, and the rotational effects appear. The present results provide the basic, useful information on practically important lean combustion.