Study on enhancing flame stability using zirconia-based coating walls

doi:10.11949/0438-1157.20211129

Abstract

Abstract:

From the perspective of controlling the thermal and chemical properties of the combustion chamber wall, this paper uses atmospheric plasma spraying technology to prepare two ceramic coating walls, ZrO₂ and ZrO₂+Al₂O₃, and studies coating material effects on the flame characteristic of methane/air mixtures in a narrow channel based on the planar laser induced fluorescence technique. Coating characterization shows that thermal spraying treatment can realize partial Al-Zr solid solution, and increases the oxygen content distributed on the surfaces. Mixing Al₂O₃ also renders a larger thermal conductivity of the coating wall and then enhances streamwise heat conduction. Finally, slot combustion tests confirm that using ZrO₂+Al₂O₃ coating wall can effectively reduce the quenching distance and show a better flame stability under various wall temperatures and equivalence ratios rather than pure ZrO₂ case. In particular, as the wall temperature increases and channel spacing decreases, the OH radical concentration in the close vicinity of ZrO₂+Al₂O₃ coating wall and in flame core areas are both elevated significantly.

Key words: ZrO₂+Al₂O₃ coating, OH-PLIF, lattice oxygen, quenching distance, enhanced stable combustion

摘要：

从调控燃烧室壁面热和化学性能角度出发，利用大气等离子喷涂技术制备了ZrO₂和ZrO₂+Al₂O₃两种陶瓷涂层壁面，并结合OH平面激光诱导荧光（OH-PLIF）技术研究了涂层材料对平板通道内甲烷/空气预混火焰特性的影响。涂层材料表征结果显示，高温热喷涂能使混合材料内部形成部分Zr-Al固溶体，表面分布的晶格氧含量明显增加。ZrO₂基混合材料热导率的增加也会增强流向导热作用。狭缝燃烧实验证实相比使用纯ZrO₂涂层，混合一定量Al₂O₃在不同壁温、当量比条件下均能有效降低火焰淬熄间距，表现出更好的燃烧稳定性。特别是随着壁温升高、通道间距缩小，ZrO₂+Al₂O₃近壁面区域以及火焰核心区OH基浓度均显著提高。

关键词: 氧化锆+氧化铝涂层, OH-PLIF, 晶格氧, 淬熄间距, 强化稳燃

CLC Number:

TK 16

Fan LI, Aolin JIANG, Haolin YANG, Xiaojun ZENG, Liqiao JIANG, Xiaohan WANG. Study on enhancing flame stability using zirconia-based coating walls[J]. CIESC Journal, 2021, 72(11): 5883-5892.

李凡, 姜奥林, 杨浩林, 曾小军, 蒋利桥, 汪小憨. 氧化锆基涂层壁面改善火焰稳定性研究[J]. 化工学报, 2021, 72(11): 5883-5892.

Figures/Tables 11

Fig.1 Powder morphology (SEM and TEM) and size distribution of the ZrO2 (a) and ZrO2+Al2O3 (b) coating powders

Fig.2 Schematic setup of experiments (a) and detailed structure of assembled slot burner (b)

Fig.3 XRD (a), XPS (b), and H2-TPR (c) characterization results of the coating materials before and after thermal spraying

Table 1 Analysis of lattice parameter， oxygen distribution， reduction temperature and hydrogen consumption of the coating materials before and after spraying

涂层壁面材料		晶格常数a/b/c	O_A/(O_L+O_A)	O_L/(O_L+O_A)	还原温度 /K	耗氢量/(μmol/g)
ZrO₂	喷涂前	5.13/5.19/5.30	51.7%	48.3%	641.7	203.5
ZrO₂	喷涂后	5.06/5.06/5.06	81.6%	18.4%	660.8	416.9
ZrO₂+Al₂O₃	喷涂前	5.14/5.20/5.31	60.2%	39.8%	639.3	189.4
ZrO₂+Al₂O₃	喷涂后	3.58/3.58/5.17	59.9%	40.1%	630.1	209.4

Fig.4 Variation of quenching distance with coating material at the equivalence ratio of 1.00—1.25 under the wall temperature conditions of 373K (a), 473K (b), 573K (c), 673K (d), and 773K (e)

Table 2 Thermophysical parameters of the different coating materials measured by plate heat flow method

涂层粉末材料	T_t/K	ρ/ (kg/m³)	c_p/ (J/(g·K) )	α/ (cm²/s)	λ_e/ (W/(m·K) )
ZrO₂	373	3.32	0.52	0.00288	0.497
ZrO₂	1073	3.32	0.94	0.00183	0.377
ZrO₂+Al₂O₃	373	3.10	0.94	0.00334	0.973
ZrO₂+Al₂O₃	1073	3.10	1.24	0.00189	0.727

Table 3 Theoretical calculation of the thermal conductivities for different coating plate materials

板材材料类型	λ_c/(W/(m·K))
板材材料类型	低温环境	高温环境
ZrO₂	1.98	2.25
Al₂O₃	29.73	7.25
ZrO₂+Al₂O₃	9.69	4.37

Fig.5 Variation of reduction rate of quenching distance with the wall temperature and equivalence ratio

Fig.6 Effect of wall materials on the OH maximum fluorescence intensity in flame cores

Fig.7 Contour distribution of the OH concentration under different coating materials

Fig.8 Normalized OH fluorescence intensity of the flame closed to coating walls

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