Investigation of NO formation in premixed adiabatic laminar flames of H₂/CO syngas and air by saturated laser-induced fluorescence and kinetic modeling

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• 作者：Zhihua Wang^a ; Yajun Zhou^a ; Ronald Whiddon ; ^a ; ^{rjwhiddon@zju.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Yong He^a ; Kefa Cen^a ; Zhongshan Li^b
• 关键词：Premixed flame ; Syngas ; Dilution ; Laser-saturation fluorescence ; NO formation
• 刊名：Combustion and Flame
• 出版年：2016
• 出版时间：February 2016
• 年：2016
• 卷：164
• 期：Complete
• 页码：283-293
• 全文大小：3251 K

文摘

A series of experiments were performed to investigate the relationship between syngas composition (H₂/CO/CO₂/N₂/O₂) and NO formation. Laser-saturated fluorescence measurements of NO in a premixed syngas flat flame from a heat flux burner were recorded for various fuel compositions, dilution ratios and equivalence ratios. Quantitative measurements were compared with the predictions from CHEMKIN software using four different chemical mechanisms, i.e., GRI mech 3.0, Chemical Reaction Engineering and Chemical Kinetics 1407, GDF-Kin 3.0, and the Mendiara and Glarborg mechanism; each mechanism included reaction subsets for NOx formation. These models were validated against a CH₄ flame; the GDF-Kin 3.0 mechanism produced the best agreement with measurements. NO measurements for CO/H₂ syngas fuel with 50% CO₂ dilution at various equivalence ratios found the maximum NO production near stoichiometry. The majority of NO produced for these conditions is predicted to come from the combination of the NNH and N₂O pathways. Investigation of NO production during combustion of different CO/H₂ ratio syngas diluted with 60% N₂ showed that increasing the H₂ fraction decreased the total NO concentration. However, normalizing the NO production rate by the fuel mass consumption rate showed H₂ produces more NO per gram of fuel consumed. Predictions of temperature and NO rate of production along the flame axis showed that the syngas with high H₂ content had a flame front closer to the burner exit and NO production rate greater than the high CO case. Dilution of CO/H₂ syngas fuel with N₂ and CO₂ showed that CO₂ has a stronger reduction in NO emission than N₂. GDF-Kin 3.0 predicted that dilution with CO₂ caused a greater reduction in flame temperature than the same volume of N₂. Predicted NO rate of production and reaction sensitivity analysis predicted that the Zel’dovich pathway was dominant for undiluted syngas. However, as the flame temperature reduced, the Zel’dovich pathway was inhibited to a greater extent than the N₂O and NNH pathways so that, at high dilution, NO production was driven by the N₂O and NNH pathways.