Extinction mechanism of ethylene opposed-flow diffusion flame using chemical explosive mode analysis method

doi:10.11949/j.issn.0438-1157.20181008

Abstract

Abstract:

The basic methodological theory as well as its feasibility of the chemical explosion mode analysis (CEMA) method in flame extinction mechanism study was particularly emphasized. The interaction between detailed chemistry and thermal/mass mixing as well as its impact on flame extinction was analyzed. The concept of factor determines the key reaction kinetic factors that dominate the flame flameout limit of ethylene. The results show that the CEM with positive eigenvalues firstly appeared at the stoichiometric location in the near-extinction condition, so positive CEM could play as an important criterion for the detection of combustion instability. The extinction limit of opposed-flow diffusion flame resulted from the comprehensive interaction between heat release and chain branching and termination reactions. It is found that the branching reaction R32 (H+O₂ $?$ O+OH) and exothermic reaction R81(OH+CO $?$ H+CO₂) were most significant for the ethylene flame extinction limit, which could be largely broadened with the enhancements of these two recations. On the contrary, enhancement of the termination reaction R49 (H+HCO $?$ H₂+CO) was unforable to ethylene flammability. The CEMA theory with the concepts of explosive index and bifurcation index was a systematical tool to reveal the impact of detailed chemical kinetics on flame extinction mechanism.

Key words: dynamics theory, explosion, chemical reaction, computational simulation, fuel

摘要：

重点探讨了化学爆炸模式分析(CEMA)在熄火机理研究中的具体方法理论及可行性，研究了化学反应/热质混合相互作用对熄火的影响，并利用爆炸因子和分叉因子的概念，确定出主导乙烯火焰熄火极限的关键反应动力学因素。结果表明：具有正特征值的CEM首次出现在熄火极限附近火焰化学当量等值面处，因此它可作为判断熄火的重要依据。火焰的熄火极限是放热与链分支、中断反应综合作用的结果，链分支反应R32(H+O₂ $?$ O+OH)和放热反应R81(OH+CO $?$ H+CO₂)对乙烯熄火极限的影响最显著，增大这两步反应速率能极大地扩宽燃烧稳定范围；而增大链中断反应R49(H+HCO $?$ H₂+CO)的速率会缩小燃烧稳定范围。基于CEMA方法与爆炸因子、分叉因子的概念，可系统地揭示详细反应动力学对熄火的影响机理。

关键词: 动力学理论, 爆炸, 化学反应, 计算机模拟, 燃料

CLC Number:

TK 4

Yinhu KANG, Pengyuan ZHANG, Congcong LIU, Jiangze MA, Xiaofeng LU. Extinction mechanism of ethylene opposed-flow diffusion flame using chemical explosive mode analysis method[J]. CIESC Journal, 2019, 70(4): 1644-1651.

亢银虎, 张朋远, 刘葱葱, 马江泽, 卢啸风. 基于化学爆炸模式分析方法的乙烯对冲扩散火焰熄火机理[J]. 化工学报, 2019, 70(4): 1644-1651.

Figures/Tables 6

Fig.1 Diagram of 1-D ethylene opposed-flow diffusion flame

Fig.2 S-curves using detailed and reduced USC mechanisms

Fig.3 (a) S-curve of C2H4 opposed-flow diffusion flame at 50 kPa (20%C2H4/80%N2 vs 20%O2/80%N2)(P1—P5 are five typical points along S-curve); (b) Plots of sign(Re(λ e))×lg(1+|Re(λ e)|) vs temperature at stoichiometric location along the S-curve; (c) Plots of sign(Re(λ e))×lg(1+|Re(λ e)|) vs mixture fraction at points P1—P5, respectively（Re(λ e) is the real part of CEM mode）

Fig.4 (a) Governing reactions for CEM at the stoichiometric location of flame P3 and their BI values; (b) Response of S-curve after the pre-factors (Ar ) of governing reactions were multiplied by 2

Fig.5 Heat release rates of governing reactions at the stoichiometric location of flame P3(Positive heat release designates exothermicity and the negative designates endothermicity. The parenthesized red number following each reaction shows the index of its absolute heat release rate in deceasing order)

Fig.6 Governing species or temperature with their corresponding EI at stoichiometric location of P3 flame

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