Abstract:

The combustion of ammonia faces problems such as high nitrogen oxide emissions and poor combustion stability, and the concept of staged combustion is one of the ways to solve these problems. However, the complex combustion characteristics are still unclear. Experimental measurements and large eddy simulations were conducted on an in house designed axially air-staged turbulent combustion device. The fuel gas is mixture of NH₃ and CH₄ fuel, and the equivalence ratio of the primary stage maintained at 1.2, with the overall equivalence ratio between 0.4 and 0.9. The variation characteristics of nitric oxide (NO) with the total equivalence ratio were obtained through experimental measurements. Large eddy simulation combined with dynamic flame thickening model was used to perform detailed calculation and analysis of three combustion cases, and the calculated results were in good agreement with experimental data. The study revealed that NO emissions increased as the overall equivalence ratio decreased. Two combustion modes were observed within the combustion chamber: a rich-premixed golden flame of ammonia-containing gas at upstream, and a hydrogen-air diffusion blue flame at downstream. In the first-stage combustion chamber, NO emissions are mainly affected by OH, while NO generation in the second-stage combustion chamber is less affected by OH.

Key words: two-stage ammonia combustion, premixed turbulent flame, nitric oxide emission, numerical simulation, combustion experimental measurement

摘要：

氨气燃烧面临着氮氧化物排放高、燃烧稳定性差等问题，而分级燃烧概念是解决上述问题的途径之一，但其中复杂的燃烧特性尚不明确。为此，对一个自主设计的轴向空气分级氨气-甲烷湍流燃烧装置开展了详细的实验测量和大涡模拟研究。以氨/甲烷的混合物为燃料，首级当量比保持为1.2，总当量比在0.4~0.9变化，通过实验测量获得一氧化氮（NO）随总当量比的变化特性，采用大涡模拟结合动态火焰增厚模型对3个燃烧状态进行计算分析，计算结果与实验数据吻合良好。研究表明：随着总当量比的减小，NO排放呈增加的趋势；燃烧室内存在两种燃烧模式，上游是金黄色的含氨燃气富燃预混火焰，下游则是淡蓝色的氢气-空气扩散火焰为主；一级燃烧室中，NO排放主要受OH影响，而二级燃烧室中NO生成受OH影响变小。

关键词: 双级氨气燃烧, 湍流预混燃烧, 一氧化氮排放, 数值模拟, 燃烧实验测量