正十一烷/空气在宽温度范围下着火延迟的激波管研究

在加热激波管上测量了气相正十一烷/空气混合物的着火延迟时间，着火温度为宽温度范围731-1399 K，着火压力在2.02 × 10⁵和10.10 × 10⁵ Pa附近，化学计量比分别为0.5、1.0和2.0。通过监测管侧壁观测点处的反射激波压力和OH^*发射光测出着火延迟时间。实验结果显示：在910 K以上，着火延迟时间随着火温度的降低而变长，从910到780 K，着火延迟时间随着火温度的降低而变短（显示出了负温度系数效应），在780 K以下，着火延迟时间随着火温度的降低再次变长。在所研究的压力下，着火压力的增加使着火时间变短。化学计量比对着火延迟的影响在着火压力为2.02 × 10⁵和10.10 × 10⁵ Pa时是不同的，与在高温区相比，着火延迟在低温区对化学计量比非常敏感。在整个温度范围内，当前实验结果和LLNL（LawrenceLivermore National Laboratory）机理的预测值表现出了很好的一致性。现在的正十一烷/空气的着火数据和先前实验测量的正庚烷/空气、正癸烷/空气和正十二烷/空气的着火延迟时间相比较显示了着火延迟时间随着直链烷碳原子数的增加而减小。敏感度分析显示，高、低温条件下影响正十一烷着火延迟过程的反应是显著不同的。在高温条件下起最大促进作用的反应是H + O₂=O+OH，然而在低温条件下，起最大促进作用的反应是过氧十一烷基（C₁₁H₂₃O₂）的异构化反应。本文研究首次提供了正十一烷/空气的激波管着火延迟时间。

A Shock Tube Study of n-Undecane/Air Ignition Delays over a Wide Range of Temperatures

The ignition delay times of gas-phase n-undecane/air mixtures in a heated shock tube were measured over a wide range of temperatures, from 731 to 1399 K, at pressures of approximately 2.02 × 10⁵ and 10.10 × 10⁵ Pa, and at equivalence ratios of 0.5, 1.0, and 2.0. This study represents the first-ever investigation of the shock tube ignition delay times of the n-undecane/air. The ignition delay times were determined by monitoring the reflected shock pressure and OH^* emission at a location on the sidewall of the shock tube. The results show that the ignition delay time increases as the temperature is decreased above 910 K, then decreases with decreasing temperature between 910 and 780 K (thus exhibiting a negative temperature coefficient behavior), and finally increases again as the temperature is further reduced below 780 K. An increase in pressure was found to decrease the ignition delay time. The effect of the equivalence ratio on the ignition delay is different at the two experimental pressures, and the ignition delay is evidently highly sensitive to the equivalence ratio in the low temperature region compared with the high temperature region. The results obtained in this work are in good agreement with theoretical predictions generated using the LLNL (Lawrence Livermore National Laboratory) mechanism over the entire temperature range. The present data for the n-undecane/air were also compared with previously reported experimental ignition delay times for n-heptane/air, n-decane/air and ndodecane/ air, demonstrating that the ignition delay time decreases with increases in the number of carbon atoms in the n-alkane. Sensitivity analysis indicated that the reactions that primarily affect the ignition delay of nundecane at high and low temperatures are dramatically different. The most important reaction at high temperatures is H + O₂=O + OH, while at low temperatures the peroxy undecyl (C₁₁H₂₃O₂) isomerization reactions predominate.