物理化学学报 >> 2018, Vol. 34 >> Issue (6): 618-624.doi: 10.3866/PKU.WHXB201710252

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戊酸甲酯高温点火的激波管研究

卢鹏飞1,苟于单1,何九宁1,李萍1,*(),张昌华1,李象远2   

  1. 1 四川大学原子与分子物理研究所,成都 610065
    2 四川大学化学工程学院,成都 610065
  • 收稿日期:2017-08-17 发布日期:2018-03-20
  • 通讯作者: 李萍 E-mail:lpscun@scu.edu.cn
  • 基金资助:
    国家自然科学基金(91441132)

Shock Tube Study of Methyl Pentanoate Ignition at High Temperatures

Pengfei LU1,Yudan GOU1,Jiuning HE1,Ping LI1,*(),Changhua ZHANG1,Xiangyuan LI2   

  1. 1 Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, P. R. China
    2 College of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China
  • Received:2017-08-17 Published:2018-03-20
  • Contact: Ping LI E-mail:lpscun@scu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(91441132)

摘要:

戊酸甲酯是生物柴油和长链脂类燃烧过程中的中间产物之一。迄今为止,文献中还没有戊酸甲酯点火延迟的实验结果,因此对其点火特性的研究是必要的。在本文工作中,于反射激波后测量了戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气的点火延迟时间。实验条件为:戊酸甲酯/空气点火温度1050–1350 K,点火压力1.5 × 105和16 × 105 Pa,当量比0.5、1和2;戊酸甲酯/4%氧气/氩气点火温度1210–1410 K,点火压力3.5 × 105和7 × 105 Pa,当量比0.75和1.25。点火延迟时间由在距离激波管端面15毫米处的测量点测到的反射激波到达信号和CH自由基信号所决定。所得实验结果显示:对于戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气,温度或压力的增加都一定会使它们的点火延迟时间变短,但对于戊酸甲酯/空气,当量比对其点火延迟时间的影响在高低压下却是不同的(16 × 105 Pa: τign = 5.43 × 10−6Ф−0.411exp(1.73 × 102/RT),1.5 × 105 Pa: τign = 7.58 × 10−7Ф0.193exp(2.11 × 102/RT)。当压力为3.5 × 105–7 × 105 Pa时,还获得了戊酸甲酯/4%氧气/氩气点火延迟时间随点火条件的变化关系:τign = 2.80 × 10−5(10−5P)−0.446±0.032Ф0.246±0.044exp((1.88 ± 0.03) × 102/RT)。这些关系式反映了点火延迟时间对温度、压力和当量比的依赖关系,且有助于将实验数据归一到特定条件下进行比较。在本文实验条件下,由于戊酸甲酯/空气的燃料浓度远大于戊酸甲酯/4%氧气/氩气的燃料浓度,所测戊酸甲酯/空气的点火延迟时间远短于戊酸甲酯/4%氧气/氩气的点火延迟时间。通过对戊酸甲酯和其它长链脂类的点火特性比较,发现在相对低温时(空气中1200 K以下,氩气中1280 K以下),戊酸甲酯的点火延迟时间要长于其它长链脂类的点火延迟时间。已有的两个戊酸甲酯化学动力学机理都不能很好地预测本文实验结果,对戊酸甲酯机理的进一步完善是需要的。敏感度分析结果表明,支链反应H + O2 = O + OH对戊酸甲酯的高温点火起着最强的促进作用。据我们所知,本文首次报道了戊酸甲酯的高温点火延迟实验数据,研究结果对了解戊酸甲酯的点火特性非常重要,并且为完善戊酸甲酯的化学动力学机理提供了实验依据。

关键词: 点火延迟时间, 戊酸甲酯, 激波管, 敏感度分析, 动力学机理

Abstract:

Methyl pentanoate (MPE, C6H12O2) is one of the intermediate produced species during the combustion of biodiesel and long-chain methyl esters. Until now, experimental results for MPE ignition are not available in literature, hence, a study on the ignition characteristics of MPE is necessary. In the present work, the ignition delay times for the gas phase of MPE/air and MPE/4%O2/Ar were measured behind reflected shock waves. Experimental conditions included temperatures of 1050–1350 K, pressures of 1.5 × 105 and 16 × 105 Pa, and equivalence ratios of 0.5, 1, and 2 for MPE/air, and temperatures of 1210–1410 K, pressures of 3.5 × 105 and 7 × 105 Pa, and equivalence ratios of 0.75 and 1.25 for MPE/4%O2/Ar. Ignition delay time was determined using the arrival of a reflected shock wave and the excited CH radical emission at the observation location, which is at a distance of 15 mm from the shock tube end wall. The obtained results indicate that as temperature or pressure increases, the ignition delay time of MPE/air and MPE/4%O2/Ar mixtures decreases definitely. However, the effect of the equivalence ratio on the ignition delay time of MPE/air is different at high and low pressures, (16 × 105 Pa: τign = 5.43 × 10−6Ф−0.411exp(1.73 × 102/RT), 1.5 × 105 Pa: τign = 7.58 × 10−7Ф0.193exp(2.11 × 102/RT). In addition, an ignition delay correlation, i.e., τign = 2.80 × 10−5(10−5P)−0.446±0.032Ф0.246±0.044exp((1.88 ± 0.03) × 102/RT)), is developed for MPE/4%O2/Ar in a pressure range of 3.5 × 105–7 × 105 Pa. This correlation shows that ignition delay depends on temperature, pressure, and the equivalence ratio, and it is useful for scaling experimental data to certain conditions for comparison purposes. In addition, the ignition delay times of MPE/air are considerably lower than that of MPE/4%O2/Ar because the fuel concentration of MPE/air is significantly higher than that of MPE/4%O2/Ar in the present ignition conditions. The ignition delay time behaviors of MPE were compared with those of other long-chain methyl esters, and results indicate that the ignition delay times of MPE are longer than those of long-chain methyl esters at lower temperatures (under 1200 K for MPE/air, under 1280 K for MPE/4%O2/Ar). The two available chemical kinetic mechanisms of MPE cannot predict current measured data accurately, a further refinement of the mechanisms of MPE ignition is required. Sensitivity analyses indicate that the chain-branching reaction, H + O2 = O + OH, plays the most promoting role in the high temperature ignition of MPE. To the best of the authors’ knowledge, this is the first study to report the high temperature experimental ignition delay data of MPE. The results of this study are useful for understanding the ignition characteristics of MPE and for providing measured data to refine the chemical kinetic mechanism of MPE.

Key words: Ignition delay time, Methyl pentenoate, Shock tube, Sensitivity analysis, Kinetic mechanism

MSC2000: 

  • O643