On the mechanism of magnetic field effect on methane explosion
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摘要: 为了揭示磁场对甲烷爆炸特征的影响机理，开展了磁场对甲烷爆炸影响实验，得出了磁场对甲烷爆炸压力、火焰传播速度、爆炸产物组分及体积分数的影响规律。利用Chemkin-Pro软件模拟甲烷爆炸链式反应过程，得到了甲烷爆炸过程中的关键自由基和基元反应。通过理论计算，对不同自由基在磁场作用下的受力进行分析，揭示了磁场对甲烷爆炸的影响机理。研究结果表明，磁场能够降低甲烷爆炸压力和火焰传播速度，降低CO和CO2的生成量，增加甲烷的残余量；•H、•O、•OH、•CH3、•CH2O是甲烷爆炸的关键自由基，由于•O的磁化率较高，被吸引到磁感线密集的区域，•O与其他自由基的碰撞几率减少，从而降低•HCO→CO→CO2的链式反应速率，导致CO和CO2生成量降低，且甲烷爆炸强度降低。Abstract: To study the effect mechanism of magnetic fields on methane explosion, an experiment was carried out by detonating the premixed gas of methane with the volume fraction of 9.5% and air as the rest constituent in a magnetic fields. Effect patterns of magnetic fields on methane explosion characteristics emerged based on the explosion pressure measured by pressure sensors and flame propagation velocity measured by detonation velocity meter. The gas after explosion was quantitatively sampled by gas sampler, and the volume fraction of reactants and products was detected by flue gas analyzer and gas chromatograph. Thus, the effect patterns of magnetic fields on the volume fraction of methane explosion products and reactants was obtained. The experimental results show that in the magnetic fields, the maximum explosion pressure of methane is decreased by 27.33%, and the explosion pressure rise rate is decreased by 40.96%. Along the flame propagation direction, the magnetic fields first promote and then suppress the flame propagation velocity of methane explosion, and the suppression effect is stronger than the promotion effect. Under the magnetic fields, the average flame propagation velocity of methane explosion is decreased by 16.39%. The volume fraction of reactants and products show obvious differences. The residue of methane and oxygen increased by 28.81% and 66.98%, respectively. The production of CO and CO2 decreased by 20.00% and 12.90%, respectively. Combined with sensitivity analysis, the methane explosion chain reaction process is simulated by the Chemkin-Pro software to derive the key radical and radical reactions in the methane explosion process. The •H, •O, •OH, •CH3, •CH2O are the key free radicals of methane explosion. Through theoretical calculation, the forces of different free radicals under the action of magnetic fields are analyzed. Combined with the reaction paths analysis, the effect mechanism of magnetic fields on methane explosion was explored. Due to the high magnetic susceptibility of •O, it is attracted to areas with dense magnetic induction line. The collision probability of •O with other free radicals is reduced, thereby reducing the rate of the •HCO→CO→CO2 chain reaction, resulting in a decrease in the production of CO and CO2, which ultimately leads to a decrease in methane explosion intensity.
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Key words:
- magnetic field /
- free radicals /
- magnetic susceptibility /
- reaction paths /
- chain reaction
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图 1 磁场影响可燃气体爆炸实验装置
Figure 1. Experimental apparatus for combustible gas explosion affected by magnetic fields
图 3 甲烷爆炸的最大爆炸压力和爆炸压力上升速率
Figure 3. Maximum explosion pressure and explosion pressure rise rate of methane explosion
图 4 火焰传播速度和火焰平均传播速度
Figure 4. Explosion flame propagation velocity and flame average propagation velocity
图 7 有无磁场下CH4生成CO和CO2的反应路径
Figure 7. Reaction pathways for the formation of CO and CO2 from CH4 with and without a magnetic field
表 1 甲烷爆炸反应物和产物的体积分数
Table 1. Volume fraction of reactants and products on methane explosion
组分 体积分数/% 无磁场 有磁场 甲烷 0.004 7 0.006 1 氧气 1.06 1.77 一氧化碳 0.44 0.35 二氧化碳 0.31 0.27 
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表 2 甲烷爆炸数值模拟初始参数
Table 2. Initial parameters for numerical simulation of methane explosions
体积分数/% 温度/K 压力/kPa 时间/s CH4 N2 O2 9.500 71.495 19.005 1200 101 0.05
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表 3 298 K下自由基的
${\boldsymbol{n}} $ 、$ {\boldsymbol{S}}_{\boldsymbol{i}} $ 、$ {{\boldsymbol{\ \mu}} }_{\bf{s}} $ 和${{\boldsymbol{\ \chi}} }_{{\boldsymbol{i}}}$ Table 3. n,
$ {\boldsymbol{S}}_{\boldsymbol{i}} $ ,$ {{\boldsymbol{\ \mu}} }_{\bf{s}} $ and$ {{\boldsymbol{\ \chi}} }_{{\boldsymbol{i}}} $ of free radicals at 298 K自由基 n $ {S}_{i} $ $ {\mu }_{\mathrm{s}} $/ (10−23 A·m2) $ {\chi }_{i} $/(10−6 m3·kg) •H 1 1/2 1.61 15.83 •O 2 2/2 2.62 2.64 •OH 1 1/2 1.61 1.24 •CH3 1 1/2 1.61 1.06 •CH2O 2 2/2 2.62 1.41
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表 4 影响CH4生成CO和CO2的关键基元反应
Table 4. Important elementary reactions affecting formation of CO and CO2 from CH4
基元反应 反应类型 •HCO+•O=CO+•OH 生成 •HCO= CO+•H 生成 CO+•O=CO2 生成 CO+•OH=CO2+•H 生成 •HCO+O=CO2+•H 生成 CO2+•CH2=•CH2O+CO 消耗
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