ABSTRACT

Axial-fuel-staged combustion is a promising approach to control NO_x emission at high combustor outlet temperatures by shortening the residence time of burnt gas in high-temperature region. In this paper, an axial-fuel-staged MILD combustor was studied experimentally. The combustor consists of a first MILD burner producing hot burnt gases and a secondary transverse jet nozzle injecting premixed fuel and air mixtures. By varying the secondary stage equivalence ratio (Φ₂) at several constant overall equivalence ratios (Φ_t), NO_x reduction (up to 35%) has been achieved at higher Φ_t but failed at lower Φ_t. And by increasing Φ₂ at constant first stage equivalence ratios (Φ₁), a continuous NO_x emission increase was observed, which is insensitive to the variation of Φ₁. Furthermore, the liftoff behavior of the reaction region was also studied and it was found to play important roles in the dilution of the jet mixtures, as well as OH* intensities and NO_x emissions. With the decrease of Φ₁, the OH* chemiluminescence images present a decreased OH* intensity when Φ₂ is lean but an increased OH* intensity when Φ₂ is rich. Finally, an opposed-flow flame calculation was performed and the experimental results were well-supported by this numerical study.

摘要

轴向燃料分级燃烧是有前途的方法，以控制NO _X通过缩短燃烧废气中的停留时间在高温区域在高温的燃烧器出口温度的发射。在本文中，对轴向燃料分级的 MILD 燃烧器进行了实验研究。燃烧器由产生热燃烧气体的第一个 MILD 燃烧器和喷射预混燃料和空气混合物的第二个横向喷嘴组成。通过在几个恒定的总当量比 (Φ _t ) 下改变二级当量比 (Φ ₂ )，在较高的 Φ _t下已实现NO _x减少（高达 35%），但在较低的 Φ _t下失败。并且通过增加 Φ ₂在恒定的第一阶段当量比 (Φ ₁ ) 下，观察到连续的 NO _x排放增加，这对 Φ ₁的变化不敏感。此外，还研究了反应区的升空行为，发现它在喷射混合物的稀释以及 OH* 强度和 NO _x排放方面起着重要作用。随着Φ ₁的减小，当Φ ₂贫时OH* 化学发光图像显示出降低的OH* 强度，而当Φ ₂富时则OH* 强度增加。最后，进行了对流火焰计算，该数值研究很好地支持了实验结果。