Effects of fuel stratification on flow field and flame structure of multi-stage swirling methane combustion

doi:10.11949/0438-1157.20241182

Abstract

Abstract:

The flow field, flame structure and heat release distribution of center-staged swirl combustion were measured by particle image velocimetry (PIV), OH-plane laser induced fluorescence (OH-PLIF) and CH* chemiluminescence, and the effect of fuel stratification on the characteristics of methane staged combustion was studied. Partially premixed methane/air mixtures were adopted in experiment, and the fuel stratification was attained through varied stratification ratios (SR) and global equivalence ratio. The results show that with lower SR, the primary recirculation zone (PRZ) expands radially due to combustion-induced thermal expansion, but with increased SR, radial contraction of the PRZ can occur. With increased SR, the pilot stage equivalence ratio is increased and the pilot fuel consumption is reduced, thus the remaining fuel can be transported downstream to react with the main stage excess air, which makes the HRR region move towards downstream; simultaneously, a small HRR region is formed in the PRZ with the remaining fuel. It is found that with lower SR, the main stage flame is stabilized by mixing its flame brush with the pilot stage, but with higher SR, combustion in the lip recirculation zone (LRZ) is also pronounced which contributes largely to the flame stabilization. Effects of the global equivalence ratio are similar to the SR, which can reinforce the fuel stratification and then cause expanded mixing region and weaken the pilot stage flame. Also, it enhances the LRZ combustion and makes it more essential for the main stage flame stabilization.

Key words: methane, multi-stage combustion, stability, fuel stratification, PIV, flame structur

摘要：

利用粒子图像测速（PIV）、OH平面激光诱导荧光（OH-PLIF）和CH*化学发光等技术，测量了中心分级旋流燃烧流场、火焰结构和热释放分布，研究了燃料分层对甲烷分级燃烧特性影响规律。实验采用部分预混的甲烷/空气燃料，燃料分层通过调控分层比和全局当量比实现。结果表明，低分层比下燃烧热膨胀使中心回流区（PRZ）沿径向扩张，分层比增加时PRZ可沿径向收缩。分层比增加时，值班级当量比提高、燃料消耗不足，剩余燃料输运至下游与主燃级过量空气反应，导致热释放区向下游迁移，同时在PRZ中也形成小热释放区。研究发现，低分层比下主燃级火焰依赖与值班级火焰融合维持稳定，而随分层比增加，台阶回流区（LRZ）燃烧对火焰稳定也起到关键作用。发现全局当量比与分层比作用相似，它强化燃料分层作用，使值班级混合区增大、燃烧减弱，但也可增强LRZ燃烧，使其对主燃级火焰稳定作用更显著。

关键词: 甲烷, 多级燃烧, 稳定性, 燃料分层, 粒子图像测速, 火焰结构

CLC Number:

V 231.2

Weijie ZHANG, Jiawen HE, Yiming ZHANG, Deli LI, Guangya HU, Xiao CAI, Jinhua WANG, Zuohua HUANG. Effects of fuel stratification on flow field and flame structure of multi-stage swirling methane combustion[J]. CIESC Journal, 2025, 76(4): 1754-1764.

张玮杰, 何甲文, 张一鸣, 李德立, 胡光亚, 蔡骁, 王金华, 黄佐华. 燃料分层对多级旋流甲烷燃烧流场和火焰结构影响研究[J]. 化工学报, 2025, 76(4): 1754-1764.

Figures/Tables 11

Fig.1 Schematic of the staged swirl combustor

Fig.2 PIV and OH-PLIF laser diagnostic systems

Table 1 Operation conditions

工况	$Φ_{p}$	$Φ_{m}$	$Φ$	SR
SR1	0.50	0.50	0.50	1
SR2	0.86	0.43	0.50	2
SR3	1.13	0.38	0.50	3
PHI-0.5	0.86	0.43	0.50	2
PHI-0.6	1.02	0.51	0.60	2
PHI-0.7	1.20	0.60	0.70	2

Table 1 Operation conditions

工况	$Φ_{p}$	$Φ_{m}$	$Φ$	SR
SR1	0.50	0.50	0.50	1
SR2	0.86	0.43	0.50	2
SR3	1.13	0.38	0.50	3
PHI-0.5	0.86	0.43	0.50	2
PHI-0.6	1.02	0.51	0.60	2
PHI-0.7	1.20	0.60	0.70	2

Fig.3 Flow fields with different SR

Fig.4 The HRR and vortex distributions with different SR

Fig.5 Digital images of flames with different SR

Fig.6 Flame structures with different SR

Fig.7 Normalized OH signal intensity distributions along the radial direction

Fig.8 Flow fields with different global equivalence ratios

Fig.9 The HRR distributions with different global equivalence ratios

Fig.10 Flame structure with different global equivalence ratios

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