正十一烷/空气在宽温度范围下着火延迟的激波管研究

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.