カーボンフリーアンモニア燃焼

抄録

Recent advances in the research and development of ammonia combustion are introduced. They are mainly promoted by the Cross-ministerial Strategic Innovation Promotion Program (SIP), “Energy Carrier”. Ammonia is a potential chemical substance not only for a hydrogen energy carrier but also a carbon free fuel. Ammonia also has advantages in terms of storage and transportation because the thermal properties are almost the same as those of propane. The subjects of ammonia combustion research are on low combustion intensity, low radiation intensity, as well as high NOx emission. In this article, recently obtained fundamental ammonia flame characteristics, such as the features of NO formation, laminar burning velocity, Markstein length and reaction enhancement by hydrogen addition are summarized. Flame structures and burnt gas characteristics were experimentally and numerically evaluated. NO mole fraction decreased with an increase in equivalence ratio and it is caused by NH_i (i = 2, 1, 0) generated from excess NH₃ in the mixture. Laminar burning velocities and Markstein lengths were evaluated from spherically propagating flames up to 0.5 MPa. The maximum value of laminar burning velocity of ammonia/air is less than 7 cm/s and is about 1/5 of that of methane/air flame. 1D flame simulation with detailed reaction mechanisms were also performed and it was showed that the quantitatively predicted laminar burning velocities were inaccurate. The laminar burning velocity exponentially increases with the increase in the hydrogen ratio. On the other hand, the Markstein length varies non-monotonically with with an increase in the hydrogen ratio.