Physical and Chemical Effects of CO2 Addition on CH4/H2 Flames on a Jet in Hot Coflow (JHC) Burner

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• 作者：Yaojie Tu ; Kai Su ; Hao Liu ; Sheng Chen ; Zhaohui Liu ; Chuguang Zheng
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：February 18, 2016
• 年：2016
• 卷：30
• 期：2
• 页码：1390-1399
• 全文大小：758K
• ISSN：1520-5029

文摘

Moderate or intense low-oxygen dilution (MILD) combustion is a promising technology for energy savings and pollutants emission reduction, and it has been experimentally shown that the MILD regime can be achieved more easily when using CO<sub>2sub> as diluent with respect to N<sub>2sub> [Li, P.; Combust. Flame 2013, 160 (5), 933−946]. Since CO<sub>2sub> is different from N<sub>2sub> in both physical and chemical properties, the present study aims at distinguishing the physical and chemical effects of CO<sub>2sub> addition on the establishment of MILD combustion. A jet in hot coflow (JHC) burner firing CH<sub>4sub>/H<sub>2sub> blended fuel is numerically modeled coupled with a detailed chemical kinetics mechanism. Following the examination of grid independency and model validation, the differences in combustion temperature, minor and major species formations as well as the CH<sub>4sub> oxidation pathway are compared by, respectively, replacing N<sub>2sub> with CO<sub>2sub> or X (artificial CO<sub>2sub>) in low-oxygen coflow. An interesting phenomenon is presented that the chemical effects of CO<sub>2sub> play a comparable role in the suppression of temperature rise to the physical effects. However, with the replacement of N<sub>2sub> by CO<sub>2sub>, the contribution of chemical effects to temperature reduction is gradually weakened. Moreover, the chemical effects of CO<sub>2sub> are responsible for the ignition delay as well as the enhanced CO emission when is CO<sub>2sub> replacing N<sub>2sub>, which is due to the inhibition of CH<sub>4sub> oxidation through Routes I (CH<sub>4sub> → CH<sub>3sub> → CH<sub>2sub>(S)/CH<sub>2sub> → (CH → CH<sub>2sub>O →) HCO → CO → CO<sub>2sub>) and II (CH<sub>4sub> → CH<sub>3sub> → CH<sub>2sub>O → HCO → CO → CO<sub>2sub>) together with the enhanced CO<sub>2sub> dissociation by R99 (OH + CO ↔ H + CO<sub>2sub>) and R153 (CO<sub>2sub> + CH<sub>2sub>(S) ↔ CO + CH<sub>2sub>O).