The biodiesel surrogate, methyl propanoate (MP), is more reactive than methane. Mixtures of the two can be used to control combustion initiation in various combustion systems. Reported here is a shock tube study of the influence of chemical interactions resulting from mixing the two fuels on observable combustion properties, such as global chemical time scales and species time histories. Experiments are carried out at pressures of about 4, 7.4, and 10 atm covering a temperature window of 1000 to 1500 K. Using direct laser absorption, CO time histories during MP pyrolysis are obtained. The CO absorbance is further used to determine pyrolysis times by means of which the effect of temperature on MP pyrolysis is probed. Reactivity differences are first examined with the fuel concentration maintained at 3% and then with the oxygen concentration fixed at 10%. The evidence of chemical interactions during ignition is observed through a reduction of methane ignition delay times caused by MP addition. The influence is nonlinear, with the result that ignition delay times of blends of 50% of each fuel are much closer to the ignition delay times of MP, the more reactive fuel. This is understood to result from the rapid generation of radicals during MP oxidation which further react with methane in low-activation energy elementary reactions, such as OH which reacts almost barrier-less. With respect to CO formation during MP pyrolysis, the presence of methane is not observed to significantly influence the pyrolysis time, indicating limited radical withdrawal by methane during the propanoate pyrolysis as it is the case during oxidation when the chemical interactions are accentuated by the exchange of oxygen-mediated radical formation. The measured data are compared with two model predictions, showing reasonable agreement for the ignition data and discrepancies with respect to the pyrolysis data.

中文翻译：

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甲烷和丙酸甲酯高温动力学

生物柴油替代物丙酸甲酯（MP）比甲烷更具反应性。两者的混合物可用于控制各种燃烧系统中的燃烧引发。此处报告的是一个冲击管研究，研究了两种燃料混合对化学相互作用的影响对可观察到的燃烧特性的影响，例如全球化学时间尺度和物种时间历史。实验在约4、7.4和10 atm的压力下进行，覆盖1000至1500 K的温度范围。使用直接激光吸收，获得MP热解过程中的CO时间历史。CO吸光度还用于确定热解时间，通过该时间可以探测温度对MP热解的影响。首先在燃料浓度保持在3％的情况下检查反应性差异，然后在氧气浓度固定在10％的条件下进行检查。通过减少因添加MP而引起的甲烷点火延迟时间，可以观察到点火过程中发生化学相互作用的证据。该影响是非线性的，结果是每种燃料的50％的混合物的点火延迟时间与反应性更高的MP的点火延迟时间非常接近。据了解，这是由于在MP氧化过程中自由基的快速产生而引起的，该自由基在低活化能基本反应中进一步与甲烷反应，例如几乎无障碍反应的OH。关于MP热解过程中的CO生成，未观察到甲烷的存在会显着影响热解时间，这表明在丙酸酯热解过程中甲烷限制了自由基的吸收，就像在氧化过程中通过交换氧介导的自由基形成来加重化学相互作用时一样。将测得的数据与两个模型预测值进行比较，显示出点火数据的合理一致性和相对于热解数据的差异。